Android

FindViewBindings, All ways to bind views Veronika Bae Android Developer. GDG Incheon Korea, veronika.bae

1. Butter Knife 2. Kotlin Android Extensions 3. Data Binding 4. View Binding Intro findViewById?

findViewById

findViewById How to use public final class R { /* ... */ public static final int button_ok = 0x7f090133; /* ... */ } Button okButton = findViewById(R.id.button_ok) AAPT generates

Button okButton = findViewById(R.id.button_ok) findViewById Problems 1. Casting Button okButton = (Button)findViewById(R.id.button_ok) ImageView okButton = findViewById(R.id.button_ok) API 25 API 26 Class Cast Exception

findViewById Problems 1. Casting API 25 View.java @Nullable public final View findViewById(@IdRes int id) { if (id < 0) { return null; } return findViewTraversal(id); } Button okButton = (Button)findViewById(R.id.button_ok)

findViewById Problems 1. Casting API 26 Button okButton = findViewById(R.id.button_ok) @Nullable public final T findViewById(@IdRes int id){ if (id == NO_ID) { return null; } return findViewTraversal(id); } View.java

findViewById Problems 2. Null Pointer Exception API 26 Button okButton = findViewById(R.id.button_ok) @Nullable public final T findViewById(@IdRes int id){ if (id == NO_ID) { return null; } return findViewTraversal(id); } View.java

findViewById Problems 2. Null Pointer Exception API 26 Button okButton = findViewById(R.id.button_ok) @Nullable public final T findViewById(@IdRes int id){ if (id == NO_ID) { return null; } return findViewTraversal(id); } View.java Null Pointer Exception

findViewById Problems 3. Boilerplate code class SomethingView @JvmOverloads constructor( context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0 ) : RelativeLayout(context, attrs, defStyleAttr) { private val itemGroup: LinearLayout private val itemGroupTitle: TextView private val someText: ImageView private val someText2: TextView private val someImage: ImageView private val someImage2: ImageView private val itemImage: ImageView private val itemImage2: ImageView /* .... */ init { View.inflate(context, R.layout.some_view, this) itemGroup = findViewById(R.id.item_group) itemGroupTitle = findViewById(R.id.item_group_title) someText = findViewById(R.id.some_text) someText2 = findViewById(R.id.some_text2) someImage = findViewById(R.id.some_image) someImage2 = findViewById(R.id.some_image2) itemImage = findViewById(R.id.item_image) itemImage2 = findViewById(R.id.item_image2) /* ... */ } }

findViewById Hidden costs @Nullable public final T findViewById(@IdRes int id) { if (id == NO_ID) { return null; } return findViewTraversal(id); } View.java

findViewById Hidden costs @Nullable public final T findViewById(@IdRes int id) { if (id == NO_ID) { return null; } return findViewTraversal(id); } protected T findViewTraversal(@IdRes int id) { if (id == mID) { return (T) this; } return null; } View.java

@Override protected T findViewTraversal(@IdRes int id) { if (id == mID) { return (T) this; } final View[] where = mChildren; final int len = mChildrenCount; for (int i = 0; i < len; i++) { View v = where[i]; if ((v.mPrivateFlags & PFLAG_IS_ROOT_NAMESPACE) == 0) { v = v.findViewById(id); if (v != null) { return (T) v; } } } return null; } ViewGroup.java

@Override protected T findViewTraversal(@IdRes int id) { if (id == mID) { return (T) this; } final View[] where = mChildren; final int len = mChildrenCount; for (int i = 0; i < len; i++) { View v = where[i]; if ((v.mPrivateFlags & PFLAG_IS_ROOT_NAMESPACE) == 0) { v = v.findViewById(id); if (v != null) { return (T) v; } } } return null; } ViewGroup.java Same as View

@Override protected T findViewTraversal(@IdRes int id) { if (id == mID) { return (T) this; } final View[] where = mChildren; final int len = mChildrenCount; for (int i = 0; i < len; i++) { View v = where[i]; if ((v.mPrivateFlags & PFLAG_IS_ROOT_NAMESPACE) == 0) { v = v.findViewById(id); if (v != null) { return (T) v; } } } return null; } ViewGroup.java Poor performance

Butter Knife

Butter Knife How to use http://jakewharton.github.io/butterknife/ Deprecated This tool is now deprecated. Please switch to view binding

Butter Knife How to use @BindView(R.id.hello) Button helloButton; helloButton.setText(sayHello); ButterKnife.bind(this);

Butter Knife How it works ButterKnife.bind(this); public class SimpleActivity_ViewBinding implements Unbinder { /* ... */ view = Utils.findRequiredView(source, R.id.hello, "field 'hello', method 'sayHello', . . .); target.hello = Utils.castView(view, R.id.hello, "field 'hello'", Button.class); } New Java Class : Original Class_ViewBinding

Butter Knife How it works view = Utils.findRequiredView(source, R.id.hello, "field 'hello', method 'sayHello', . . .”) public static View findRequiredView(View source, @IdRes int id, String who){ View view = source.findViewById(id); if (view != null) { return view; } /* … */ }

Kotlin Android Extensions

Kotlin Android Extensions How to use https://youtrack.jetbrains.com/issue/KT-42121 “Deprecate Kotlin Android Extensions compiler plugin.”

Kotlin Android Extensions How to use “Deprecate Kotlin Android Extensions compiler plugin.” As the @Parcelize functionality is extracted the rest of the Android Extensions functionality can be deprecated in favour of View Binding. The existing Android Extensions plugin will continue to work, however, a warning message will be shown.

Kotlin Android Extensions How to use apply plugin: 'kotlin-android-extensions' build.gradle

Kotlin Android Extensions How to use apply plugin: 'kotlin-android-extensions' build.gradle import kotlinx.android.synthetic.main.fragment_first.* import kotlinx.android.synthetic.main.fragment_first.view.* textViewFirst.text = "Hello, World"

Kotlin Android Extensions How to use import kotlinx.android.synthetic.main.fragment_first.* import kotlinx.android.synthetic.main.fragment_first.view.* textViewFirst.text = "Hello, World" import kotlinx.android.synthetic.{product flavor}.{layout}.*

Kotlin Android Extensions How to use import kotlinx.android.synthetic.main.fragment_first.* import kotlinx.android.synthetic.main.fragment_first.view.* textViewFirst.text = "Hello, World" import kotlinx.android.synthetic.{product flavor}.{layout}.* Synthetic Property

Kotlin Android Extensions How it works Tools → Kotlin, Show Kotlin ByteCode Bytecode Decompile

Kotlin Android Extensions How it works import kotlinx.android.synthetic.main.fragment_first.* textViewFirst.text = "Hello, World" TextView var10000 = (TextView)this._$_findCachedViewById(id.textViewFirst) Intrinsics.checkExpressionValueIsNotNull(var10000, "textViewFirst") var10000.setText((CharSequence)"Hello, World") Tools → Kotlin, Show Kotlin ByteCode Bytecode Decompile

Kotlin Android Extensions How it works private HashMap _$_findViewCache; public View _$_findCachedViewById(int var1) { if (this._$_findViewCache == null) { this._$_findViewCache = new HashMap(); } View var2 = (View)this._$_findViewCache.get(var1); if (var2 == null) { var2 = this.findViewById(var1); this._$_findViewCache.put(var1, var2); } return var2; }

Kotlin Android Extensions How it works private HashMap _$_findViewCache; public View _$_findCachedViewById(int var1) { if (this._$_findViewCache == null) { this._$_findViewCache = new HashMap(); } View var2 = (View)this._$_findViewCache.get(var1); if (var2 == null) { var2 = this.findViewById(var1); this._$_findViewCache.put(var1, var2); } return var2; }

Kotlin Android Extensions How it works public void onDestroyView() { super.onDestroyView(); this._$_clearFindViewByIdCache(); } public void _$_clearFindViewByIdCache() { if(this._$_findViewCache != null) { this._$_findViewCache.clear(); } } Fragment

Fragment View Created Fragment View Destroyed Fragment View LifeCycle Fragment Added Fragment Destroyed Fragment LifeCycle

Kotlin Android Extensions Caution Synthetic Property Not Real Property View Cache

Kotlin Android Extensions Caution fun FirstFragment.a() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } import kotlinx.android.synthetic.main.activity_main.* class FirstFragment : Fragment() Used View Cache

Kotlin Android Extensions Caution fun Fragment.b() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } fun FirstFragment.a() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } import kotlinx.android.synthetic.main.activity_main.* class FirstFragment : Fragment() Used View Cache Not Used View Cache

Kotlin Android Extensions Caution fun FirstFragment.a() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } public final void a(@NotNull FirstFragment $this$a) { . . . TextView var10000 = (TextView)$this$a._$_findCachedViewById(id.textViewFirst) . . . var10000 = (TextView)$this$a._$_findCachedViewById(id.textViewFirst) . . . var10000.setVisibility(4) } Used View Cache Decompile

Kotlin Android Extensions Caution fun Fragment.b() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } Not Used View Cache public final void b(@NotNull Fragment $this$b) { TextView var10000 = (TextView)$this$b.getView().findViewById(id.textViewFirst); . . . var10000.setText((CharSequence)"Hidden view"); var10000 = (TextView)$this$b.getView().findViewById(id.textViewFirst); . . . var10000.setVisibility(4); } Decompile

Kotlin Android Extensions Caution import kotlinx.android.synthetic.main.activity_main.* fun FirstFragment.a() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } fun Fragment.b() { textViewFirst.text = "Hidden view" textViewFirst.visibility = View.INVISIBLE } Used View Cache Not Used View Cache class FirstFragment : Fragment()

Kotlin Android Extensions Caution Custom Layout layout_custom.xml Common Mistake Case

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.itemView.itemTitle1.text = "hello1" with(holder.itemView) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.itemView.itemTitle1.text = "hello1" with(holder.itemView) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions

Kotlin Android Extensions Caution Decompile import kotlinx.android.synthetic.main.layout_custom.view.* public void onBindViewHolder( @NotNull ViewHolder holder, int position) { if (holder instanceof SearchAdapter.CustomViewHolder) { View var10000 = holder.itemView; TextView var8 = (TextView)var10000.findViewById(id.itemTitle1); var8.setText((CharSequence)”hello1"); View var3 = holder.itemView; var8 = (TextView)var3.findViewById(id.itemTitle2); var8.setText((CharSequence)"hello2"); } }

Kotlin Android Extensions Caution Decompile import kotlinx.android.synthetic.main.layout_custom.view.* public void onBindViewHolder( @NotNull ViewHolder holder, int position) { if (holder instanceof SearchAdapter.CustomViewHolder) { View var10000 = holder.itemView; TextView var8 = (TextView)var10000.findViewById(id.itemTitle1); var8.setText((CharSequence)”hello1"); View var3 = holder.itemView; var8 = (TextView)var3.findViewById(id.itemTitle2); var8.setText((CharSequence)"hello2"); } } Calling every time

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.itemView.itemTitle1.text = "hello1" with(holder.itemView) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions A common class

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: CustomViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.itemView.itemTitle1.text = "hello1" with(holder.itemView) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.itemView.itemTitle1.text = "hello1" with(holder.itemView) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.customLayout.itemTitle1.text = "hello1" with(holder.customLayout) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) } Kotlin Android Extensions

import kotlinx.android.synthetic.main.layout_custom.view.* class SearchAdapter : RecyclerView.Adapter() { override fun onCreateViewHolder(. . .) : RecyclerView.ViewHolder { return CustomViewHolder(CustomLayout(parent.context)) } override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) { if (holder is CustomViewHolder) { holder.customLayout.itemTitle1.text = "hello1" with(holder.customLayout) { itemTitle2.text = "hello1" } } } class CustomViewHolder(private val customLayout: CustomLayout) : RecyclerView.ViewHolder(customLayout) { // declare view properties - itemTitle1, itemTitle2 } } Kotlin Android Extensions

DataBinding, ViewBinding

DataBinding, ViewBinding How to use Google IO 19

DataBinding, ViewBinding How to use build.gradle DataBinding ViewBinding Gradle 3.6 dataBinding { enabled = true } viewBinding { enabled = true } Gradle 4.0 buildFeatures { dataBinding = true } buildFeatures { viewBinding = true }

DataBinding How to use activity_sample.xml Elements are wrapped in a layout tag Expressions are defined inside a data

DataBinding How to use activity_sample.xml Elements are wrapped in a layout tag

DataBinding How to use SampleActivity.xml class SampleActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val binding : ActivitySampleBinding = DataBindingUtil.setContentView( this,R.layout.activity_sample) binding.dataBindingFirst.text = "hello data binding!” } } (android:id=“@+id/data_binding_first”) ActivitySampleBinding = LayoutFileName + Binding = activity_sample.xml + Binding

ViewBinding How to use activity_view_sample.xml

ViewBinding How to use activity_view_sample.xml

ViewBinding How to use SampleViewActivity.xml class SampleViewActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val binding = ActivityViewSampleBinding.inflate(layoutInflater) setContentView(binding.root) } } binding.viewBindingFirst.text = "hello view binding!" No! ( R.layout.activity_view_sample )

ViewBinding Caution private var _binding: ResultProfileBinding? = null private val binding get() = _binding!! override fun onCreateView(. . .): View? { _binding = ResultProfileBinding.inflate( inflater, container, false) val view = binding.root return view } override fun onDestroyView() { super.onDestroyView() _binding = null } Fragment Should be released

Fragment View Created Fragment View Destroyed Fragment View LifeCycle Fragment Added Fragment Destroyed Fragment LifeCycle

DataBinding How it works val binding : ActivitySampleBinding = DataBindingUtil.setContentView(this, R.layout.activity_sample) create binding class public abstract class ActivitySampleBinding extends ViewDataBinding { } ???

DataBinding How it works public abstract class ActivitySampleBinding extends ViewDataBinding { @NonNull public final TextView dataBindingFirst; protected ActivitySampleBinding(... TextView dataBindingFirst) { super(...); this.dataBindingFirst = dataBindingFirst; } @NonNull public static ActivitySampleBinding inflate(. . .) { return inflate(..., DataBindingUtil.getDefaultComponent()); } } generated from SampleActivity

DataBinding How it works activity_sample.xml activity_sample-layout.xml

DataBinding How it works

DataBinding How it works

DataBinding How it works activity_sample-layout.xml DataBinderMapperImpl.class @Override public ViewDataBinding getDataBinder(DataBindingComponent component, View view, int layoutId) { final Object tag = view.getTag(); . . . switch (localizedLayoutId) { case LAYOUT_ACTIVITYSAMPLE: { if ("layout/activity_sample_0".equals(tag)) return new ActivitySampleBindingImpl(component, view); . . . } }

DataBinding public class ActivitySampleBindingImpl extends ActivitySampleBinding{ @Nullable 
 private static final SparseIntArray sViewsWithIds; static { . . . sViewsWithIds = new android.util.SparseIntArray(); sViewsWithIds.put(R.id.data_binding_first, 1); } public ActivitySampleBindingImpl( @Nullable ..DataBindingComponent bindingComponent, @NonNull View root) { this(bindingComponent, root, mapBindings(bindingComponent, root, 2, sIncludes, sViewsWithIds)); } } activity_sample.xml activity_sample-layout.xml

DataBinding private static void mapBindings(. . .) { . . . Object objTag = view.getTag(); final String tag = (objTag instanceof String) ? (String) objTag : null; boolean isBound = false; if (isRoot && tag != null && tag.startsWith("layout")) { . . . } else if (tag != null && tag.startsWith(BINDING_TAG_PREFIX)) { . . . if (bindings[tagIndex] == null) { bindings[tagIndex] = view; } isBound = true; } else { . . . } if (!isBound) { final int id = view.getId(); if (id > 0) { int index; if (viewsWithIds != null && (index = viewsWithIds.get(id, -1)) >= 0 && bindings[index] == null) { bindings[index] = view; } } } } Activity_sample-layout.xml

DataBinding private static void mapBindings(. . .) { . . . Object objTag = view.getTag(); final String tag = (objTag instanceof String) ? (String) objTag : null; boolean isBound = false; if (isRoot && tag != null && tag.startsWith("layout")) { . . . } else if (tag != null && tag.startsWith(BINDING_TAG_PREFIX)) { . . . if (bindings[tagIndex] == null) { bindings[tagIndex] = view; } isBound = true; } else { . . . } if (!isBound) { final int id = view.getId(); if (id > 0) { int index; if (viewsWithIds != null && (index = viewsWithIds.get(id, -1)) >= 0 && bindings[index] == null) { bindings[index] = view; } } } } Activity_sample-layout.xml

DataBinding How it works activity_sample.xml android:text=“@{textValue}” activity_sample-layout.xml tag=“binding_1”>

ViewBinding public final class ActivityViewSampleBinding implements ViewBinding { @NonNull public final TextView viewBindingFirst; ... @NonNull public static ActivityViewSampleBinding bind(@NonNull View rootView) ... missingId: { id = R.id.data_binding_first; TextView viewBindingFirst = rootView.findViewById(id); if (dataBindingFirst == null) { break missingId; } return new ActivityViewSampleBinding( (LinearLayout) rootView, dataBindingFirst); } )); } }

ViewBinding public final class ActivityViewSampleBinding implements ViewBinding { @NonNull public final TextView viewBindingFirst; ... @NonNull public static ActivityViewSampleBinding bind(@NonNull View rootView) ... missingId: { id = R.id.data_binding_first; TextView viewBindingFirst = rootView.findViewById(id); if (dataBindingFirst == null) { break missingId; } return new ActivityViewSampleBinding( (LinearLayout) rootView, dataBindingFirst); } )); } }

findViewById Hidden Costs, Exceptions Butter Knife Annotation Processor, findViewbyId Kotlin Android Extensions View Caching, findViewbyId DataBinding Annotation Processor, Tag ViewBinding findViewById

ViewBinding? Find yours!

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