# This is a combination of 5 commits.

# This is the 1st commit message:

Formatting

# This is the commit message flutter#2:

Suppress lint

# This is the commit message flutter#3:

Docs, linter

# This is the commit message flutter#4:

More docs

# This is the commit message #5:

Fix whitespace:

Author: GaryQian

shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java

@@ -18,6 +18,8 @@
 import android.util.SparseArray;
 import android.view.View;
 import android.view.ViewStructure;
+import android.view.WindowInsets;
+import android.view.WindowInsetsAnimation;
 import android.view.autofill.AutofillId;
 import android.view.autofill.AutofillManager;
 import android.view.autofill.AutofillValue;
@@ -26,8 +28,6 @@
 import android.view.inputmethod.InputConnection;
 import android.view.inputmethod.InputMethodManager;
 import android.view.inputmethod.InputMethodSubtype;
-import android.view.WindowInsets;
-import android.view.WindowInsetsAnimation;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
@@ -60,6 +60,7 @@ public class TextInputPlugin {
   // details.
   private boolean isInputConnectionLocked;
 
+  @SuppressLint("NewApi")
   public TextInputPlugin(
       View view,
       @NonNull TextInputChannel textInputChannel,
@@ -72,6 +73,9 @@ public TextInputPlugin(
       afm = null;
     }
 
+    // Sets up syncing ime insets with the framework, allowing
+    // the Flutter view to grow and shrink to accomodate Android
+    // controlled keyboard animations.
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
       int mask = 0;
       if ((View.SYSTEM_UI_FLAG_HIDE_NAVIGATION & mView.getWindowSystemUiVisibility()) == 0) {
@@ -86,8 +90,8 @@ public TextInputPlugin(
               mask, // Overlay
               WindowInsets.Type.ime() // Deferred
               );
-      view.setWindowInsetsAnimationCallback(imeSyncCallback);
-      view.setOnApplyWindowInsetsListener(imeSyncCallback);
+      mView.setWindowInsetsAnimationCallback(imeSyncCallback);
+      mView.setOnApplyWindowInsetsListener(imeSyncCallback);
     }
 
     this.textInputChannel = textInputChannel;
@@ -161,12 +165,32 @@ public void sendAppPrivateCommand(String action, Bundle data) {
 
   // Loosely based off of
   // https://github.com/android/user-interface-samples/blob/master/WindowInsetsAnimation/app/src/main/java/com/google/android/samples/insetsanimation/RootViewDeferringInsetsCallback.kt
-  // When the IME is shown or hidden, it sends an onApplyWindowInsets call with the
-  // final state of the IME. This defers the final call to allow the animation to
-  // take place before re-calling onApplyWindowInsets after animation completion.
+  //
+  // When the IME is shown or hidden, it immediately sends an onApplyWindowInsets call
+  // with the final state of the IME. This initial call disrupts the animation, which
+  // causes a flicker in the beginning.
+  //
+  // To fix this, this class extends WindowInsetsAnimation.Callback and implements
+  // OnApplyWindowInsetsListener. We capture and defer the initial call to
+  // onApplyWindowInsets while the animation completes. When the animation
+  // finishes, we can then release the call by invoking it in the onEnd callback
+  //
+  // The WindowInsetsAnimation.Callback extension forwards the new state of the
+  // IME inset from onProgress() to the framework. We also make use of the
+  // onPrepare and onStart callbacks to detect which calls to onApplyWindowInsets
+  // would interrupt the animation and defer it.
+  //
+  // By implementing OnApplyWindowInsetsListener, we are able to capture Android's
+  // attempts to call the FlutterView's onApplyWindowInsets. When a call to onPrepare
+  // and subsequently onStart occurs, we can mark any non-animation calls to
+  // onApplyWindowInsets() that ocurrs between prepare and start as deferred by 
+  // using this class' custom implementation to cache the WindowInsets passed in.
+  // When onEnd indicates the end of the animation, the deferred call is dispatched
+  // again, this time avoiding any flicker since the animation is now complete.
   @VisibleForTesting
   @TargetApi(30)
   @RequiresApi(30)
+  @SuppressLint({"NewApi", "Override"})
   class ImeSyncDeferringInsetsCallback extends WindowInsetsAnimation.Callback
       implements View.OnApplyWindowInsetsListener {
     private int overlayInsetTypes;
@@ -192,8 +216,13 @@ public WindowInsets onApplyWindowInsets(View view, WindowInsets windowInsets) {
         lastWindowInsets = windowInsets;
       }
       if (deferredInsets) {
+        // While animation is running, we consume the insets to prevent disrupting
+        // the animation, which skips this implementation and calls the view's
+        // onApplyWindowInsets directly to avoid being consumed here.
         return WindowInsets.CONSUMED;
       }
+      // If no animation is happening, pass the insets on to the view's own
+      // inset handling.
       return view.onApplyWindowInsets(windowInsets);
     }
 
@@ -214,7 +243,8 @@ public WindowInsetsAnimation.Bounds onStart(
     }
 
     @Override
-    public WindowInsets onProgress(WindowInsets insets, List<WindowInsetsAnimation> runningAnimations) {
+    public WindowInsets onProgress(
+        WindowInsets insets, List<WindowInsetsAnimation> runningAnimations) {
       if (!deferredInsets) {
         return insets;
       }
@@ -230,6 +260,12 @@ public WindowInsets onProgress(WindowInsets insets, List<WindowInsetsAnimation>
       }
       WindowInsets.Builder builder = new WindowInsets.Builder(lastWindowInsets);
       // Overlay the ime-only insets with the full insets.
+      //
+      // The IME insets passed in by onProgress assumes that the entire animation
+      // occurs above any present navigation and status bars. This causes the
+      // IME inset to be too large for the animation. To remedy this, we merge the
+      // IME inset with other insets present via a subtract, which causes the IME
+      // inset to be overlaid with any bars present.
       Insets newImeInsets =
           Insets.of(
               0,
@@ -240,7 +276,10 @@ public WindowInsets onProgress(WindowInsets insets, List<WindowInsetsAnimation>
                       - insets.getInsets(overlayInsetTypes).bottom,
                   0));
       builder.setInsets(deferredInsetTypes, newImeInsets);
-      // Directly call onApplyWindowInsets as we want to skip this class' version of this call.
+      // Directly call onApplyWindowInsets of the view as we do not want to pass through
+      // the onApplyWindowInsets defined in this class, which would consume the insets
+      // as if they were a non-animation inset change and cache it for re-dispatch in
+      // onEnd instead.
       view.onApplyWindowInsets(builder.build());
       return insets;
     }
@@ -315,6 +354,10 @@ public void unlockPlatformViewInputConnection() {
   public void destroy() {
     platformViewsController.detachTextInputPlugin();
     textInputChannel.setTextInputMethodHandler(null);
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+      mView.setWindowInsetsAnimationCallback(null);
+      mView.setOnApplyWindowInsetsListener(null);
+    }
   }
 
   private static int inputTypeFromTextInputType(

shell/platform/android/test/io/flutter/plugin/editing/TextInputPluginTest.java

@@ -34,8 +34,11 @@
 import android.view.inputmethod.InputMethodManager;
 import android.view.inputmethod.InputMethodSubtype;
 import io.flutter.embedding.android.FlutterView;
+import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterJNI;
 import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.embedding.engine.loader.FlutterLoader;
+import io.flutter.embedding.engine.renderer.FlutterRenderer;
 import io.flutter.embedding.engine.systemchannels.TextInputChannel;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.common.JSONMethodCodec;
@@ -50,6 +53,7 @@
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
 import org.robolectric.annotation.Config;
@@ -62,6 +66,9 @@
 @Config(manifest = Config.NONE, shadows = TextInputPluginTest.TestImm.class)
 @RunWith(RobolectricTestRunner.class)
 public class TextInputPluginTest {
+  @Mock FlutterJNI mockFlutterJni;
+  @Mock FlutterLoader mockFlutterLoader;
+
   // Verifies the method and arguments for a captured method call.
   private void verifyMethodCall(ByteBuffer buffer, String methodName, String[] expectedArgs)
       throws JSONException {
@@ -655,7 +662,7 @@ public void ime_windowInsetsSync() {
         spy(new FlutterEngine(RuntimeEnvironment.application, mockFlutterLoader, mockFlutterJni));
     FlutterRenderer flutterRenderer = spy(new FlutterRenderer(mockFlutterJni));
     when(flutterEngine.getRenderer()).thenReturn(flutterRenderer);
-    flutterView.attachToFlutterEngine(flutterEngine);
+    testView.attachToFlutterEngine(flutterEngine);
 
     WindowInsetsAnimation animation = mock(WindowInsetsAnimation.class);
     when(animation.getTypeMask()).thenReturn(WindowInsets.Type.ime());