Øredev 2017: Measure. Layout. Draw. Repeat.

Huyen's presentation at Øredev 2017 on custom Views and ViewGroups in Android.

Transcript

1. 1
   MEASURE.
   LAYOUT.
   DRAW.
   REPEAT.
   HUYEN TUE DAO
   @QUEENCODEMONKEY
   

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2. 2
   MEASURE.
   LAYOUT.
   DRAW.
   REPEAT.
   CUSTOM VIEWS
   WHY?
   CUSTOM LOOK/BEHAVIOR
   REUSABILITY/MODULARITY
   PERFORMANCE
   

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3. 3
   MEASURE.
   LAYOUT.
   DRAW.
   REPEAT.
   CUSTOM VIEWS
   WHY NOT?
   DIFFICULT
   TIME-CONSUMING
   DRAWING/INTERACTIONS/A11Y
   → ON YOUR OWN
   

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4. 4
   MEASURE.
   LAYOUT.
   DRAW.
   REPEAT.
   HOW ANDROID DRAWS VIEWS
   HOW TO GO CUSTOM
   DRAW
   MEASURE
   VIEW GROUPS
   LAYOUT
   

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5. R
   MEASURE
   LAYOUT
   DRAW
   INFLATION/INSTANTIATION
   DEPTH-FIRST
   TRAVERSAL
   HOW ANDROID
   DRAWS VIEWS
   onLayout()
   onDraw()
   onMeasure()
   

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6. R
   PARENT PASSES
   CONSTRAINTS
   CHILD CALCULATES
   MEASURED WIDTH/HEIGHT
   MEASURE
   HOW ANDROID
   DRAWS VIEWS
   onMeasure()
   LAYOUT
   onLayout()
   DRAW
   onDraw()
   MEASURE OWN
   CHILDREN (IF ANY)
   

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7. R
   PARENT SIZES AND
   POSITIONS CHILD
   MEASURE
   LAYOUT
   DRAW
   HOW ANDROID
   DRAWS VIEWS
   onMeasure()
   onLayout()
   onDraw()
   

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8. PARENT DRAWS
   PARENT TELLS
   CHILDREN TO DRAW
   MEASURE
   LAYOUT
   DRAW
   0
   1
   Z
   parent
   children
   HOW ANDROID
   DRAWS VIEWS
   onMeasure()
   onLayout()
   onDraw()
   

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9. DIFFERENT WAYS TO
   GO CUSTOM
   VIEW VIEWGROUP
   EXTEND
   EXISTING
   CUSTOM LAYOUTS ON ANDROID, @LUCASRATMUNDO
   EXTEND
   BASE
   CUSTOM EXTENDED*
   TWEAK BEHAVIOR
   ARGUABLY SIMPLEST
   COMPOSITE
   MODULAR UI
   LAYOUT REUSE
   FLAT CUSTOM
   CUSTOM DRAWING/BEHAVIOR
   PERFORMANCE
   CUSTOM COMPOSITE
   CUSTOM LAYOUT LOGIC
   PERFORMANCE
   

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10. WHAT DO YOU NEED
    TO IMPLEMENT?
    VIEW
    MEASURE
    LAYOUT
    DRAW
    onMeasure()
    onLayout()
    onDraw()
    NO
    NO
    YES
    BUT YOU SHOULD
    REUSABILITY/FLEXIBILITY
    VIEW HAS NO CHILDREN
    REQUIRED FOR VIEW
    TO APPEAR
    

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11. 11
    WHAT WE WILL BUILD.
    GREAT, HUH?
    

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12. 12
    /**
    * An interface for a view implementing a tally counter.
    !*/
    public interface TallyCounter {
    /**
    * Reset the counter.
    !*/
    void reset();
    /**
    * Increment the counter.
    !*/
    void increment();
    /**
    * @return The current count of the counter.
    !*/
    int getCount();
    /**
    * Set the counter value.
    !*/
    void setCount(int count);
    }
    

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13. VIEW CONSTRUCTORS
    CREATE NEW FROM CODE
    View(ContextAcontext)
    CREATE FROM XML
    View(ContextBcontext, AttributeSetBattrs)
    CREATE FROM XML WITH A STYLE FROM A THEME ATTRIBUTE
    View(ContextCcontext, AttributeSetCattrs,
    intCdefStyleAttr)
    CREATE FROM XML WITH A STYLE FROM A THEME ATTRIBUTE OR STYLE RESOURCE
    View(ContextDcontext, AttributeSetDattrs,
    intDdefStyleAttr, intDdefStyleRes)
    A DEEP DIVE INTO ANDROID VIEW CONSTRUCTORS
    @DANLEW42
    

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14. 14
    public TallyCounterView(ContextAcontext) {
    this(context, null);
    }
    public TallyCounterView(ContextBcontext, AttributeSetBattrs) {
    super(context, attrs);
    }A
    

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15. 15
    public TallyCounterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    }A
    

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16. 16
    public TallyCounterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    !// Set up paints for canvas drawing.
    backgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    backgroundPaint.setColor(ContextCompat.getColor(context, R.color.colorPrimary));
    linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    linePaint.setColor(ContextCompat.getColor(context, R.color.colorAccent));
    linePaint.setStrokeWidth(1f);
    numberPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    numberPaint.setColor(ContextCompat.getColor(context, android.R.color.white));
    }A
    

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17. 17
    public TallyCounterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    !// Set up paints for canvas drawing.
    backgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    backgroundPaint.setColor(ContextCompat.getColor(context, R.color.colorPrimary));
    linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    linePaint.setColor(ContextCompat.getColor(context, R.color.colorAccent));
    linePaint.setStrokeWidth(1f);
    numberPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    numberPaint.setColor(ContextCompat.getColor(context, android.R.color.white));
    !// Set the number text size to be 64sp.
    !// Translate 64sp…
    numberPaint.setTextSize(
    Math.round(64f * getResources().getDisplayMetrics().scaledDensity));
    }A
    

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18. 18
    public TallyCounterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    !// Set up paints for canvas drawing.
    backgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    backgroundPaint.setColor(ContextCompat.getColor(context, R.color.colorPrimary));
    linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    linePaint.setColor(ContextCompat.getColor(context, R.color.colorAccent));
    linePaint.setStrokeWidth(1f);
    numberPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    numberPaint.setColor(ContextCompat.getColor(context, android.R.color.white));
    !// Set the number text size to be 64sp.
    !// Translate 64sp…
    numberPaint.setTextSize(
    Math.round(64f * getResources().getDisplayMetrics().scaledDensity));
    !// Allocate objects needed for canvas drawing here.
    backgroundRect = new RectF();
    !// Initialize drawing measurements.
    cornerRadius = Math.round(2f * getResources().getDisplayMetrics().density);
    }A
    

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19. 19
    public TallyCounterView(Context context, AttributeSet attrs) {
    super(context, attrs);
    !// Set up paints for canvas drawing.
    backgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    backgroundPaint.setColor(ContextCompat.getColor(context, R.color.colorPrimary));
    linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    linePaint.setColor(ContextCompat.getColor(context, R.color.colorAccent));
    linePaint.setStrokeWidth(1f);
    numberPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
    numberPaint.setColor(ContextCompat.getColor(context, android.R.color.white));
    !// Set the number text size to be 64sp.
    !// Translate 64sp…
    numberPaint.setTextSize(
    Math.round(64f * getResources().getDisplayMetrics().scaledDensity));
    !// Allocate objects needed for canvas drawing here.
    backgroundRect = new RectF();
    !// Initialize drawing measurements.
    cornerRadius = Math.round(2f * getResources().getDisplayMetrics().density);
    !// Do initial count setup.
    setCount(0);
    }A
    

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20. 20
    @Override
    protected void onDraw(Canvas canvas) {
    }A
    WHAT WE WANT
    0000
    

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21. 21
    @Override
    protected void onDraw(Canvas canvas) {
    !// Grab canvas dimensions.
    final int canvasWidth = canvas.getWidth();
    final int canvasHeight = canvas.getHeight();
    !// Calculate horizontal center.
    final float centerX = canvasWidth * 0.5f;
    }A
    WHAT WE WANT
    0000
    

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22. 22
    @Override
    protected void onDraw(Canvas canvas) {
    !// Grab canvas dimensions.
    final int canvasWidth = canvas.getWidth();
    final int canvasHeight = canvas.getHeight();
    !// Calculate horizontal center.
    final float centerX = canvasWidth * 0.5f;
    !// Draw the background.
    backgroundRect.set(0f, 0f, canvasWidth, canvasHeight);
    canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, backgroundPaint);
    }A
    WHAT WE WANT
    0000
    

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23. 23
    @Override
    protected void onDraw(Canvas canvas) {
    !// Grab canvas dimensions.
    final int canvasWidth = canvas.getWidth();
    final int canvasHeight = canvas.getHeight();
    !// Calculate horizontal center.
    final float centerX = canvasWidth * 0.5f;
    !// Draw the background.
    backgroundRect.set(0f, 0f, canvasWidth, canvasHeight);
    canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, backgroundPaint);
    !// Draw baseline.
    final float baselineY = Math.round(canvasHeight * 0.6f);
    canvas.drawLine(0, baselineY, canvasWidth, baselineY, linePaint);
    }A
    WHAT WE WANT
    0000
    

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24. 24
    @Override
    protected void onDraw(Canvas canvas) {
    !// Grab canvas dimensions.
    final int canvasWidth = canvas.getWidth();
    final int canvasHeight = canvas.getHeight();
    !// Calculate horizontal center.
    final float centerX = canvasWidth * 0.5f;
    !// Draw the background.
    backgroundRect.set(0f, 0f, canvasWidth, canvasHeight);
    canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, backgroundPaint);
    !// Draw baseline.
    final float baselineY = Math.round(canvasHeight * 0.6f);
    canvas.drawLine(0, baselineY, canvasWidth, baselineY, linePaint);
    !// Draw text.
    }A
    WHAT WE WANT
    0000
    

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25. 25
    @Override
    protected void onDraw(Canvas canvas) {
    !// Grab canvas dimensions.
    final int canvasWidth = canvas.getWidth();
    final int canvasHeight = canvas.getHeight();
    !// Calculate horizontal center.
    final float centerX = canvasWidth * 0.5f;
    !// Draw the background.
    backgroundRect.set(0f, 0f, canvasWidth, canvasHeight);
    canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, backgroundPaint);
    !// Draw baseline.
    final float baselineY = Math.round(canvasHeight * 0.6f);
    canvas.drawLine(0, baselineY, canvasWidth, baselineY, linePaint);
    !// Draw text.
    !// Measure the width of text to display.
    final float textWidth = numberPaint.measureText(displayedCount);
    !// Figure out an x-coordinate that will center the text in the canvas.
    final float textX = Math.round(centerX - textWidth * 0.5f);
    !// Draw.
    canvas.drawText(displayedCount, textX, baselineY, numberPaint);
    }A
    WHAT WE WANT
    0000
    

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26. View Slide

27. REFLECTING STATE CHANGES
    MARK A VIEW AS DIRTY (NEEDS A RE-DRAW)
    invalidate()
    RE-DRAWN “AT SOME POINT IN THE FUTURE”
    BE MORE PRECISE:
    invalidate(int l, int t, int r, int b)
    

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28. 28
    !//
    !// TallyCounter interface
    !//
    @Override
    public void reset() {
    setCount(0);
    }
    @Override
    public void increment() {
    setCount(count + 1);
    }
    @OverrideA
    public void setCount(int count) {
    count = Math.min(count, MAX_COUNT);
    this.count = count;
    !// Create the string here.
    this.displayedCount = String.format(Locale.getDefault(), "%04d", count);
    }A
    @Override
    public int getCount() {
    return count;
    }
    

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29. 29
    @OverrideA
    public void setCount(int count) {
    count = Math.min(count, MAX_COUNT);
    this.count = count;
    !// Create the string here.
    this.displayedCount = String.format(Locale.getDefault(), "%04d", count);
    }A
    

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30. 30
    @OverrideA
    public void setCount(int count) {
    count = Math.min(count, MAX_COUNT);
    this.count = count;
    !// Create the string here.
    this.displayedCount = String.format(Locale.getDefault(), "%04d", count);
    invalidate();
    }A
    

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31. View Slide

32. THINGS TO REMEMBER WHEN DRAWING
    NO ALLOCATIONS IN ONDRAW.
    SERIOUSLY.
    INVALIDATE ONLY WHEN YOU NEED.
    INVALIDATE ONLY WHAT YOU NEED.
    TEXT IS POSITIONED AT THE
    BASELINE.
    DRAW IN PX.
    THINK IN DP AND SP.
    

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33. View Slide

34. WHERE’S THAT OTHER BUTTON?
    android:id="@+id/increment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="48dp"
    android:text="@string/click" !/>
    android:id="@+id/tally_counter"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="40dp" !/>
    android:id="@+id/reset"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop=“40dp"
    android:text="@string/reset" !/>
    

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35. HOW MEASUREMENTS
    ARE MADE
    CHILD
    PARENT
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    setLayoutParams()
    How a child tells its parent how
    it wants to be laid out.
    MarginLayoutParams
    LinearLayout.LayoutParams
    1Child defines LayoutParams
    in XML or Java
    getLayoutParams()
    

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36. HOW MEASUREMENTS
    ARE MADE
    CHILD
    PARENT
    How a parent communicates
    constraints to children
    child.measure()
    int = { mode | size }
    AT_MOST X → Be any size up to X
    EXACTLY X → Be exactly X
    UNSPECIFIED → No constraints
    1
    2
    Child defines LayoutParams
    in XML or Java
    Parent calculates MeasureSpecs
    and passes to child.measure()
    

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37. HOW MEASUREMENTS
    ARE MADE
    Must call; otherwise → runtime
    exception.
    CHILD
    PARENT
    setMeasuredDimension()
    1
    2
    3
    Child defines LayoutParams
    in XML or Java
    Parent calculates MeasureSpecs
    and passes to child.measure()
    Child calculates width/height;
    setMeasuredDimension()
    getMeasuredWidth()
    getMeasuredHeight()
    

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38. HOW MEASUREMENTS
    ARE MADE
    Child defines LayoutParams
    in XML or Java
    1
    Parent calculates MeasureSpecs
    and passes to child.measure()
    2
    Child calculates width/height;
    setMeasuredDimension()
    3
    Parent calls child.layout();
    final child size/position.
    4
    CHILD
    PARENT
    child.layout()
    getWidth()
    getHeight()
    

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39. 39
    private int reconcileSize(int contentSize, int measureSpec) {
    final int mode = MeasureSpec.getMode(measureSpec);
    final int specSize = MeasureSpec.getSize(measureSpec);
    switch (mode) {Z
    case MeasureSpec.EXACTLY:
    return specSize;
    case MeasureSpec.AT_MOST:
    if (contentSize < specSize) {B
    return contentSize;
    }Belse {C
    return specSize;
    }C
    case MeasureSpec.UNSPECIFIED:
    default:
    return contentSize;
    }Z
    }Z
    

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40. 40
    private int reconcileSize(int contentSize, int measureSpec) {
    final int mode = MeasureSpec.getMode(measureSpec);
    final int specSize = MeasureSpec.getSize(measureSpec);
    switch (mode) {A
    case MeasureSpec.EXACTLY:
    return specSize;
    case MeasureSpec.AT_MOST:
    if (contentSize < specSize) {B
    return contentSize;
    }Belse {C
    return specSize;B
    }C
    case MeasureSpec.UNSPECIFIED:
    default:
    return contentSize;B
    }A
    }Z
    

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41. 41
    private int reconcileSize(int contentSize, int measureSpec) {
    final int mode = MeasureSpec.getMode(measureSpec);
    final int specSize = MeasureSpec.getSize(measureSpec);
    switch (mode) {A
    case MeasureSpec.EXACTLY:
    return specSize;A
    case MeasureSpec.AT_MOST:
    if (contentSize < specSize) {B
    return contentSize;Q
    }Belse {C
    return specSize;B
    }C
    case MeasureSpec.UNSPECIFIED:
    default:
    return contentSize;B
    }A
    }Z
    

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42. 42
    private int reconcileSize(int contentSize, int measureSpec) {
    final int mode = MeasureSpec.getMode(measureSpec);
    final int specSize = MeasureSpec.getSize(measureSpec);
    switch (mode) {A
    case MeasureSpec.EXACTLY:
    return specSize;A
    case MeasureSpec.AT_MOST:
    if (contentSize < specSize) {B
    return contentSize;Q
    }Belse {C
    return specSize;B
    }C
    case MeasureSpec.UNSPECIFIED:
    default:
    return contentSize;
    }A
    }Z
    

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43. HOWEVER, YOU SHOULD
    ACTUALLY USE THIS
    public static int View.resolveSize(int size, int measureSpec)
    

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44. 44
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    }A
    

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45. 45
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    }A
    

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46. 46
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    }A
    

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47. 47
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    !// Estimate maximum possible height of text.
    final float maxTextHeight = -fontMetrics.top + fontMetrics.bottom;
    }A
    

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48. 48
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    !// Estimate maximum possible height of text.
    final float maxTextHeight = -fontMetrics.top + fontMetrics.bottom;
    !// Add padding to maximum width calculation.
    final int desiredWidth =
    Math.round(maxTextWidth + getPaddingLeft() + getPaddingRight());
    }A
    

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49. 49
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    !// Estimate maximum possible height of text.
    final float maxTextHeight = -fontMetrics.top + fontMetrics.bottom;
    !// Add padding to maximum width calculation.
    final int desiredWidth =
    Math.round(maxTextWidth + getPaddingLeft() + getPaddingRight());
    !// Add padding to maximum height calculation.
    final int desiredHeight =
    Math.round(maxTextHeight * 2f + getPaddingTop() + getPaddingBottom());
    }A
    

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50. 50
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    !// Estimate maximum possible height of text.
    final float maxTextHeight = -fontMetrics.top + fontMetrics.bottom;
    !// Add padding to maximum width calculation.
    final int desiredWidth =
    Math.round(maxTextWidth + getPaddingLeft() + getPaddingRight());
    !// Add padding to maximum height calculation.
    final int desiredHeight =
    Math.round(maxTextHeight * 2f + getPaddingTop() + getPaddingBottom());
    !// Reconcile size that this view wants to be with the size
    !// that the parent will let it be.
    final int measuredWidth = reconcileSize(desiredWidth, widthMeasureSpec);
    final int measuredHeight = reconcileSize(desiredHeight, heightMeasureSpec);
    }A
    

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51. 51
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    A
    final Paint.FontMetrics fontMetrics = numberPaint.getFontMetrics();
    !// Measure maximum possible width of text.
    final float maxTextWidth = numberPaint.measureText(MAX_COUNT_STRING);
    !// Estimate maximum possible height of text.
    final float maxTextHeight = -fontMetrics.top + fontMetrics.bottom;
    !// Add padding to maximum width calculation.
    final int desiredWidth =
    Math.round(maxTextWidth + getPaddingLeft() + getPaddingRight());
    !// Add padding to maximum height calculation.
    final int desiredHeight =
    Math.round(maxTextHeight * 2f + getPaddingTop() + getPaddingBottom());
    !// Reconcile size that this view wants to be with the size
    !// that the parent will let it be.
    final int measuredWidth = reconcileSize(desiredWidth, widthMeasureSpec);
    final int measuredHeight = reconcileSize(desiredHeight, heightMeasureSpec);
    !// Store the final measured dimensions.
    setMeasuredDimension(measuredWidth, measuredHeight);
    }A
    

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52. View Slide

53. WHAT DO YOU NEED
    TO IMPLEMENT?
    VIEWGROUP
    MEASURE
    LAYOUT
    DRAW
    YES
    YES
    NO
    HAVE TO MEASURE EACH
    CHILD: child.measure()
    (ABSTRACT) HAVE TO LAYOUT
    EACH CHILD: child.layout()
    DOES NOT DRAW BY DEFAULT
    setWillNotDraw
    onMeasure()
    onLayout()
    onDraw()
    

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54. View Slide

55. 55
    xmlns:android="http:"//schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingTop="@dimen/list_item_padding_vertical"
    android:paddingBottom="@dimen/list_item_padding_vertical"
    android:paddingStart="0dp"
    android:paddingEnd="@dimen/activity_horizontal_margin"
    …>
    android:id="@+id/icon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginEnd="12dp"
    android:contentDescription="@null" !/>
    android:id="@+id/title"
    android:layout_width="wrap_content"
    android:layout_height=“wrap_content" !/>
    android:id="@+id/subtitle"
    android:layout_width="wrap_content"
    android:layout_height=“wrap_content" !/>
    !
    

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56. 56
    public class SimpleListItem extends ViewGroup {
    @BindView(R.id.icon)
    ImageView icon;
    @BindView(R.id.title)
    TextView titleView;
    @BindView(R.id.subtitle)
    TextView subtitleView;
    /**
    * Constructor.
    *
    * @param context The current context.
    * @param attrs The attributes of the XML tag that is inflating the view.
    !*/
    public SimpleListItem(Context context, AttributeSet attrs) {
    super(context, attrs);
    }
    @Override
    protected void onFinishInflate() {
    super.onFinishInflate();
    ButterKnife.bind(this);
    }
    

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57. VALIDATE
    checkLayoutParams()
    VIEW WITHOUT LAYOUT PARAMETERS
    generateDefaultLayoutParams()
    VIEW WITH INVALID LAYOUT PARAMETERS
    generateLayoutParams(ViewGroup.LayoutParams p)
    VIEW WITH LAYOUT XML ATTRIBUTES
    generateLayoutParams(AttributeSet attrs)
    CUSTOM LAYOUT
    PARAMETERS
    ViewGroup.LayoutParams
    (width, height)
    MarginLayoutParams
    (width, height)
    (left, top, right, bottom)
    

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58. USEFUL MEASUREMENT
    METHODS
    MEASURE + PADDING
    measureChild(…)
    measureChildren(…)
    MEASURE SPEC + CHILD LAYOUT PARAMETERS
    getChildMeasureSpec(…)
    MEASURE + PADDING + MARGINS + SPACE USED
    measureChildWithMargins(…)
    “The heavy lifting is done
    in getChildMeasureSpec.”
    

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59. 59
    @Override
    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
    return p instanceof MarginLayoutParams;
    }
    @Override
    protected LayoutParams generateDefaultLayoutParams() {
    return new MarginLayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }
    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
    return new MarginLayoutParams(getContext(), attrs);
    }
    @Override
    protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
    return generateDefaultLayoutParams();
    }
    

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60. 60
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    }A
    WHAT WE WANT
    

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61. 61
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    !// Measure icon.
    measureChildWithMargins(icon, widthMeasureSpec, 0, heightMeasureSpec, 0);
    }A
    WHAT WE WANT
    

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62. 62
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    !// Measure icon.
    measureChildWithMargins(icon, widthMeasureSpec, 0, heightMeasureSpec, 0);
    !// Figure out how much width and height the icon used.
    MarginLayoutParams lp = (MarginLayoutParams) icon.getLayoutParams();
    int widthUsed = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int heightUsed = 0;
    }A
    WHAT WE WANT
    

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63. 63
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    !// Measure icon.
    measureChildWithMargins(icon, widthMeasureSpec, 0, heightMeasureSpec, 0);
    !// Figure out how much width and height the icon used.
    MarginLayoutParams lp = (MarginLayoutParams) icon.getLayoutParams();
    int widthUsed = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int heightUsed = 0;
    !// Measure title
    measureChildWithMargins(
    titleView,
    widthMeasureSpec, widthUsed,
    heightMeasureSpec, heightUsed
    );
    }A
    WHAT WE WANT
    

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64. 64
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    !// Measure icon.
    measureChildWithMargins(icon, widthMeasureSpec, 0, heightMeasureSpec, 0);
    !// Figure out how much width and height the icon used.
    MarginLayoutParams lp = (MarginLayoutParams) icon.getLayoutParams();
    int widthUsed = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int heightUsed = 0;
    !// Measure title
    measureChildWithMargins(
    titleView,
    widthMeasureSpec, widthUsed,
    heightMeasureSpec, heightUsed
    );
    !// Measure the Subtitle.
    measureChildWithMargins(A
    subtitleView,
    widthMeasureSpec, widthUsed,A
    heightMeasureSpec, titleView.getMeasuredHeight());
    }A
    WHAT WE WANT
    

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65. 65
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    …A
    }A
    WHAT WE WANT
    

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66. 66
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    …A
    !// Calculate this view's measured width and height.
    }A
    WHAT WE WANT
    

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67. 67
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    …A
    !// Calculate this view's measured width and height.
    !// Figure out how much total space the icon used.
    int iconWidth = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int iconHeight = icon.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
    lp = (MarginLayoutParams) titleView.getLayoutParams();
    !// Figure out how much total space the title used.
    int titleWidth = titleView.getMeasuredWidth() +
    lp.leftMargin + lp.rightMargin;
    int titleHeight = titleView.getMeasuredHeight() +
    lp.topMargin + lp.bottomMargin;
    lp = (MarginLayoutParams) subtitleView.getLayoutParams();
    !// Figure out how much total space the subtitle used.
    int subtitleWidth = subtitleView.getMeasuredWidth() +
    lp.leftMargin +lp.rightMargin;
    int subtitleHeight = subtitleView.getMeasuredHeight() +
    lp.topMargin + lp.bottomMargin;
    }A
    WHAT WE WANT
    

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68. 68
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    …A
    !// The width taken by the children + padding.
    int width = getPaddingTop() + getPaddingBottom() +
    iconWidth + Math.max(titleWidth, subtitleWidth);
    !// The height taken by the children + padding.
    int height = getPaddingTop() + getPaddingBottom() +
    Math.max(iconHeight, titleHeight + subtitleHeight);
    }A
    WHAT WE WANT
    

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69. 69
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {A
    …A
    !// The width taken by the children + padding.
    int width = getPaddingTop() + getPaddingBottom() +
    iconWidth + Math.max(titleWidth, subtitleWidth);
    !// The height taken by the children + padding.
    int height = getPaddingTop() + getPaddingBottom() +
    Math.max(iconHeight, titleHeight + subtitleHeight);
    !// Reconcile the measured dimensions with the this view's constraints and
    !// set the final measured width and height.
    setMeasuredDimension(
    resolveSize(width, widthMeasureSpec),
    resolveSize(height, heightMeasureSpec)
    );
    }A
    WHAT WE WANT
    

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70. 70
    @Override
    protected void onLayout(boolean changed,
    int left, int top, int right, int bottom) {A
    }A
    WHAT WE WANT
    

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71. 71
    @Override
    protected void onLayout(boolean changed,
    int left, int top, int right, int bottom)
    MarginLayoutParams layoutParams = (MarginLayoutParams) icon.getLayoutParams();
    !// Figure out the x-coordinate and y-coordinate of the icon.
    int x = getPaddingLeft() + layoutParams.leftMargin;
    int y = getPaddingTop() + layoutParams.topMargin;
    }A
    WHAT WE WANT
    

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72. 72
    @Override
    protected void onLayout(boolean changed,
    int left, int top, int right, int bottom) {A
    MarginLayoutParams layoutParams = (MarginLayoutParams) icon.getLayoutParams();
    !// Figure out the x-coordinate and y-coordinate of the icon.
    int x = getPaddingLeft() + layoutParams.leftMargin;
    int y = getPaddingTop() + layoutParams.topMargin;
    !// Layout the icon.
    icon.layout(x, y,
    x + icon.getMeasuredWidth(), y + icon.getMeasuredHeight());
    }A
    WHAT WE WANT
    

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73. 73
    @Override
    protected void onLayout(boolean changed,
    int left, int top, int right, int bottom) {A
    …
    !// Calculate the x-coordinate of the title: icon's right coordinate +
    !// the icon's right margin.
    x += icon.getMeasuredWidth() + layoutParams.rightMargin;
    !// Add in the title's left margin.
    layoutParams = (MarginLayoutParams) titleView.getLayoutParams();
    x += layoutParams.leftMargin;
    !// Calculate the y-coordinate of the title: this ViewGroup's top padding +
    !// the title's top margin
    y = getPaddingTop() + layoutParams.topMargin;
    !// Layout the title.
    titleView.layout(x, y,
    x + titleView.getMeasuredWidth(),
    y + titleView.getMeasuredHeight());
    }A
    WHAT WE WANT
    

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74. 74
    @Override
    protected void onLayout(boolean changed,
    int left, int top, int right, int bottom) {A
    …
    !// The subtitle has the same x-coordinate as the title.
    !// So no more calculating there.
    !// Calculate the y-coordinate of the subtitle: the title's bottom
    !// coordinate + the title's bottom margin.
    y += titleView.getMeasuredHeight() + layoutParams.bottomMargin;
    layoutParams = (MarginLayoutParams) subtitleView.getLayoutParams();
    !// Add in the subtitle's top margin.
    y += layoutParams.topMargin;
    !// Layout the subtitle.
    subtitleView.layout(x, y,
    x + subtitleView.getMeasuredWidth(), y + subtitleView.getMeasuredHeight());
    }A
    WHAT WE WANT
    

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75. 75
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    !// Measure icon.
    measureChildWithMargins(icon, widthMeasureSpec, 0, heightMeasureSpec, 0);
    !// Figure out how much width the icon used.
    MarginLayoutParams lp = (MarginLayoutParams) icon.getLayoutParams();
    int widthUsed = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int heightUsed = 0;
    !// Measure title
    measureChildWithMargins(
    titleView,
    !// Pass width constraints and width already used.
    widthMeasureSpec, widthUsed,
    !// Pass height constraints and height already used.
    heightMeasureSpec, heightUsed
    );
    !// Measure the Subtitle.
    measureChildWithMargins(
    subtitleView,
    !// Pass width constraints and width already used.
    widthMeasureSpec, widthUsed,
    !// Pass height constraints and height already used.
    heightMeasureSpec, titleView.getMeasuredHeight());
    !// Calculate this view's measured width and height.
    !// Figure out how much total space the icon used.
    int iconWidth = icon.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int iconHeight = icon.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
    lp = (MarginLayoutParams) titleView.getLayoutParams();
    !// Figure out how much total space the title used.
    int titleWidth = titleView.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int titleHeight = titleView.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
    lp = (MarginLayoutParams) subtitleView.getLayoutParams();
    !// Figure out how much total space the subtitle used.
    int subtitleWidth = subtitleView.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
    int subtitleHeight = subtitleView.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
    !// The width taken by the children + padding.
    int width = getPaddingTop() + getPaddingBottom() +
    iconWidth + Math.max(titleWidth, subtitleWidth);
    !// The height taken by the children + padding.
    int height = getPaddingTop() + getPaddingBottom() +
    Math.max(iconHeight, titleHeight + subtitleHeight);
    !// Reconcile the measured dimensions with the this view's constraints and
    !// set the final measured width and height.
    setMeasuredDimension(
    resolveSize(width, widthMeasureSpec),
    resolveSize(height, heightMeasureSpec)
    );
    }
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    MarginLayoutParams layoutParams = (MarginLayoutParams) icon.getLayoutParams();
    !// Figure out the x-coordinate and y-coordinate of the icon.
    int x = getPaddingLeft() + layoutParams.leftMargin;
    int y = getPaddingTop() + layoutParams.topMargin;
    !// Layout the icon.
    icon.layout(x, y, x + icon.getMeasuredWidth(), y + icon.getMeasuredHeight());
    !// Calculate the x-coordinate of the title: icon's right coordinate +
    !// the icon's right margin.
    x += icon.getMeasuredWidth() + layoutParams.rightMargin;
    !// Add in the title's left margin.
    layoutParams = (MarginLayoutParams) titleView.getLayoutParams();
    x += layoutParams.leftMargin;
    !// Calculate the y-coordinate of the title: this ViewGroup's top padding +
    !// the title's top margin
    y = getPaddingTop() + layoutParams.topMargin;
    !// Layout the title.
    titleView.layout(x, y, x + titleView.getMeasuredWidth(), y + titleView.getMeasuredHeight());
    !// The subtitle has the same x-coordinate as the title. So no more calculating there.
    !// Calculate the y-coordinate of the subtitle: the title's bottom coordinate +
    !// the title's bottom margin.
    y += titleView.getMeasuredHeight() + layoutParams.bottomMargin;
    layoutParams = (MarginLayoutParams) subtitleView.getLayoutParams();
    !// Add in the subtitle's top margin.
    y += layoutParams.topMargin;
    !// Layout the subtitle.
    subtitleView.layout(x, y,
    x + subtitleView.getMeasuredWidth(), y + subtitleView.getMeasuredHeight());
    }
    

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77. WHERE TO GO FROM HERE…
    ACCESSIBILITY. A11Y FTW. ADD IT.
    @KELLYSHUSTER
    CUSTOM DRAWABLES. CUSTOM DRAWABLE STATES.
    @RHARTER @MARCOSPAULOSD
    ALL THE DRAWING OPERATIONS. PATHS. FILTERS. SHADERS. OH MY!
    @ROMAINGUY @CHIUKI
    HARDWARE ACCELERATION. LEARN ABOUT LAYERS + DISPLAY LISTS.
    @WORKINGKILLS
    GO CUSTOM.
    TOUCH. GESTURES.
    @PBREAULT @CALREN24
    PERFORMANCE. MEASUREMENT. TOOLS.
    @QUEENCODEMONKEY @FRANCOISBLAVOET
    

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78. speakerdeck.com/queencodemonkey | Slides
    https:"//git.io/vFuV3 | Code
    youtube.com/androiddialogs
    randomlytyping.com
    caster.io
    HUYEN TUE DAO
    @QUEENCODEMONKEY
    THANK YOU!
    

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79. CUSTOM VIEWS/VIEWGROUPS
    Custom Views and ViewGroups (Part 1) https://caster.io/episodes/
    custom-views-and-viewgroups-part-1/
    Creating Custom Views https://developer.android.com/training/custom-
    views/index.html
    A deep dive into Android View constructors http://blog.danlew.net/
    2016/07/19/a-deep-dive-into-android-view-constructors/
    Google I/O 2013 - Writing Custom Views for Android https://youtu.be/
    NYtB6mlu7vA
    Enhancing Android UI with Custom Views https://newcircle.com/s/post/
    1663/
    tutorial_enhancing_android_ui_with_custom_views_dave_smith_video
    79
    

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80. CUSTOM VIEWS/VIEWGROUPS
    Custom Android Components http://chiuki.github.io/android-custom-
    components
    Custom Views and Performance https://youtu.be/zK2i7ivzK7M
    Taming Android UIs with Eric Burke of Square https://youtu.be/
    jF6Ad4GYjRU
    Custom Layouts on Android http://lucasr.org/2014/05/12/custom-
    layouts-on-android/
    Layout traversals on Android https://youtu.be/sdkcuvZCh1U
    Custom View Groups https://sriramramani.wordpress.com/
    2015/05/06/custom-viewgroups/
    80
    

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81. TOUCH/GESTURES
    Understanding Android Views and Gestures https://
    academy.realm.io/posts/understanding-android-views-and-
    gestures-android-meetup-chang-2017/
    Making Sense of the Touch System https://speakerdeck.com/
    pbreault/making-sense-of-the-touch-system | https://
    youtu.be/usBaTHZdXSI
    Making the View Interactive https://developer.android.com/
    training/custom-views/making-interactive.html
    81
    

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82. TEXT + DRAWING
    Typography on Android https://youtu.be/OgiZa22Zpus
    Android Textual Layout https://youtu.be/GZ0eKqvzJa8
    Hinting Around: Text Demystified https://
    www.youtube.com/watch?v=VS7co3TrgKE | https://
    speakerdeck.com/rock3r/hinting-around-android-text-
    demystified
    Calligraphy. Custom fonts in Android the easy way…
    https://github.com/chrisjenx/Calligraphy
    82
    

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83. DRAWING + DRAWABLES
    Fun with Android Shaders and Filters https://chiuki.github.io/
    android-shaders-filters
    Don’t Fear the Canvas https://youtu.be/KH8Ldp39TUk
    Custom drawable states in Android http://charlesharley.com/2012/
    programming/custom-drawable-states-in-android
    Custom Drawables http://ryanharter.com/blog/2015/04/03/
    custom-drawables/
    The Magic World of Drawables https://youtu.be/1YjB1uUfxgE
    Hardware Acceleration https://developer.android.com/guide/
    topics/graphics/hardware-accel.html
    83
    

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84. PERFORMANCE
    Loving Lean layouts https://youtu.be/gwqQT5NrhUg
    Let’s Sprinkle some #PerfMatters on your ViewGroups https://
    youtu.be/fEtyhj74JhU
    Eugenio Marletti: Clue + Highly Custom/Performant
    Components https://youtu.be/e-xWYiHAhjI
    84
    

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