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by Cyril Mottier CRAFTING CUSTOM ANDROID VIEWS

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@cyrilmottier

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No content

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https://www.capitainetrain.com/jobs

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Introduction to Android Views 1

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DEFINITION building block The basic for user interface components

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The Android SDK is bundled with several built-in Views TextView ImageView Button View ViewGroup LinearLayout RelativeLayout ProgressBar ViewStub

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View

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View TextView ImageView

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View TextView Button ImageView

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View TextView ViewGroup Button ImageView

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View TextView ViewGroup Button ImageView LinearLayout FrameLayout

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View TextView ViewGroup Button ImageView LinearLayout FrameLayout

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What are Views made for ?

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A View is responsible for MEASURING

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LAYOUTING A View is responsible for

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DRAWING A View is responsible for

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Saving UI state Managing a Drawable state Handling touch events etc. RESPONSIBILITIES

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Why develop custom components ?

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Factorize Optimize Innovate Extend 4main purposes

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1 Factorize Optimize Innovate Extend Avoid creating the same snippets of code over and over again over over over over over ove

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Factorize 2 Optimize Innovate Extend Speed up UI rendering

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Factorize Optimize 3 Innovate Extend Create something unique & groundbreaking

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Factorize Optimize Innovate 4 Extend Access View’s protected behaviors

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Creating compound controls 2

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Demo ProgressIndicator

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Extending an existing View 3

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Demo UnderlinedTextView

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Creating a completely custom View 4

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completely custom = ˝ ˝

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extend View completely custom = ˝ ˝

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completely custom = ˝ ˝ extend View ViewGroup

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passes to render a View hierarchy 3 Android does

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1 measure 2 layout 3 draw } } requestLayout() invalidate()

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MEASUREMENT void onMeasure( int widthMeasureSpec, int heightMeasureSpec); Contract Call setMeasuredDimension(int, int)

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LAYOUT void onLayout( boolean changed, int lelf, int top, int right, int bottom)

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A View can have a persisting state STATE SAVE/RESTORE

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static class SavedState extends BaseSavedState { int progress; SavedState(Parcelable superState) { super(superState); } private SavedState(Parcel in) { super(in); progress = in.readInt(); } @Override public void writeToParcel(Parcel out, int flags) { super.writeToParcel(out, flags); out.writeInt(progress); } public static final Parcelable.Creator CREATOR = new Parcelable.Creator() { public SavedState createFromParcel(Parcel in) { return new SavedState(in); } public SavedState[] newArray(int size) { return new SavedState[size]; } }; }

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static class SavedState extends BaseSavedState { int progress; SavedState(Parcelable superState) { super(superState); } private SavedState(Parcel in) { super(in); progress = in.readInt(); } @Override public void writeToParcel(Parcel out, int flags) { super.writeToParcel(out, flags); out.writeInt(progress); } public static final Parcelable.Creator CREATOR = new Parcelable.Creator() { public SavedState createFromParcel(Parcel in) { return new SavedState(in); } public SavedState[] newArray(int size) { return new SavedState[size]; } }; }

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@Override public Parcelable onSaveInstanceState() { Parcelable superState = super.onSaveInstanceState(); SavedState ss = new SavedState(superState); ss.progress = mProgress; return ss; } @Override public void onRestoreInstanceState(Parcelable state) { SavedState ss = (SavedState) state; super.onRestoreInstanceState(ss.getSuperState()); setProgress(ss.progress); }

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@Override public Parcelable onSaveInstanceState() { Parcelable superState = super.onSaveInstanceState(); SavedState ss = new SavedState(superState); ss.progress = mProgress; return ss; } @Override public void onRestoreInstanceState(Parcelable state) { SavedState ss = (SavedState) state; super.onRestoreInstanceState(ss.getSuperState()); setProgress(ss.progress); }

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To every action there is a reaction TOUCH HANDLING

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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@Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: // The first pointer went down (i.e. stop // animations and start a new drag gesture) break; case MotionEvent.ACTION_MOVE: // A pointer has moved (i.e. move the object // accordingly) break; case MotionEvent.ACTION_UP: // The last pointer went up (i.e. compute the // object’s velocity and start animating it) break; case MotionEvent.ACTION_CANCEL: // The gesture was intercepted by a parent break; } return true; }

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What if a parent View wants to intercept the gesture?

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boolean onInterceptTouchEvent(MotionEvent event) FOR EXPERTS

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SCROLLING/FLINGING A thrown object moves until it reaches its state of rest

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1Track velocity 2 Scroll/fling to state of rest

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1Track velocity @Override public boolean onTouchEvent(MotionEvent event) { if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch (event.getAction()) { case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(1000); if (mVelocityTracker.getXVelocity() > mThreshold) { // Animate the object } // no break; case MotionEvent.ACTION_CANCEL: mVelocityTracker.recycle(); mVelocityTracker = null; break; } return true; }

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1Track velocity @Override public boolean onTouchEvent(MotionEvent event) { if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch (event.getAction()) { case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(1000); if (mVelocityTracker.getXVelocity() > mThreshold) { // Animate the object } // no break; case MotionEvent.ACTION_CANCEL: mVelocityTracker.recycle(); mVelocityTracker = null; break; } return true; }

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1Track velocity @Override public boolean onTouchEvent(MotionEvent event) { if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch (event.getAction()) { case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(1000); if (mVelocityTracker.getXVelocity() > mThreshold) { // Animate the object } // no break; case MotionEvent.ACTION_CANCEL: mVelocityTracker.recycle(); mVelocityTracker = null; break; } return true; }

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1Track velocity @Override public boolean onTouchEvent(MotionEvent event) { if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch (event.getAction()) { case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(1000); if (mVelocityTracker.getXVelocity() > mThreshold) { // Animate the object } // no break; case MotionEvent.ACTION_CANCEL: mVelocityTracker.recycle(); mVelocityTracker = null; break; } return true; }

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1Track velocity @Override public boolean onTouchEvent(MotionEvent event) { if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch (event.getAction()) { case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(1000); if (mVelocityTracker.getXVelocity() > mThreshold) { // Animate the object } // no break; case MotionEvent.ACTION_CANCEL: mVelocityTracker.recycle(); mVelocityTracker = null; break; } return true; }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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2 Scroll/fling to state of rest private final Runnable mScrollRunnable = new Runnable() { @Override public void run() { if (mOverScroller.computeScrollOffset()) { final int x = mOverScroller.getCurrX(); final int y = mOverScroller.getCurrY(); // Move object to (x, y). postOnAnimation(this); } else { // animation is over } } }; public void fling() { mOverScroller.fling( mStartX, mStartY, // start x/y mVX, mVY, // velocity x/y mMinX, mMaxX, // min/max x mMinY, mMaxY); // min/max y postOnAnimation(mScrollRunnable); }

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CONSISTENCY with the rest of the platform behavior is consistent Make sure your custom View

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EdgeEffect

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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@Override public void draw(Canvas canvas) { super.draw(canvas); if (!mTopEdgeEffect.isFinished()) { canvas.save(); canvas.translate(getPaddingLeft(), 0); final int w = getWidth() - getPaddingLeft() - getPaddingRight(); mTopEdgeEffect.setSize(w, getHeight()); if (mTopEdgeEffect.draw(canvas)) { postInvalidateOnAnimation(); } canvas.restore(); } }

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This was only the drawing part ...

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mTopEdgeEffect.onAbsorb((int) velocity); .onPull((float) distance); .onRelease();

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ViewConfiguration documentation Contains methods to standard constants used in the UI for timeouts, sizes, and distances.

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private void init(Context context, AttributeSet attrs, int defStyle) { mViewConfiguration = ViewConfiguration.get(context); final int maxFlingV = mViewConfiguration .getScaledMaximumFlingVelocity(); final int touchSlop = mViewConfiguration .getScaledTouchSlop(); // ... }

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private void init(Context context, AttributeSet attrs, int defStyle) { mViewConfiguration = ViewConfiguration.get(context); final int maxFlingV = mViewConfiguration .getScaledMaximumFlingVelocity(); final int touchSlop = mViewConfiguration .getScaledTouchSlop(); // ... }

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private void init(Context context, AttributeSet attrs, int defStyle) { mViewConfiguration = ViewConfiguration.get(context); final int maxFlingV = mViewConfiguration .getScaledMaximumFlingVelocity(); final int touchSlop = mViewConfiguration .getScaledTouchSlop(); // ... }

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Conclusion 5

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Custom views are the best way for creating unique UIs

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Custom views must fit to the platform appearance

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Custom views must match to the mental model

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THANK YOU @cyrilmottier cyrilmottier.com Cyril Mottier