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

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.plugin.editing;

import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.graphics.Insets;
import android.view.View;
import android.view.WindowInsets;
import android.view.WindowInsetsAnimation;
import androidx.annotation.Keep;
import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;
import androidx.annotation.VisibleForTesting;
import java.util.List;

// 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 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
// onStart callback 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 onStart
// occurs, we can mark any non-animation calls to onApplyWindowInsets() that
// occurs between prepare and start as deferred by using this class' wrapper
// implementation to cache the WindowInsets passed in and turn the current call into
// a no-op. 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"})
@Keep
class ImeSyncDeferringInsetsCallback {
  private int overlayInsetTypes;
  private int deferredInsetTypes;

  private View view;
  private WindowInsets lastWindowInsets;
  private AnimationCallback animationCallback;
  private InsetsListener insetsListener;

  // True when an animation that matches deferredInsetTypes is active.
  //
  // While this is active, this class will capture the initial window inset
  // sent into lastWindowInsets by flagging needsSave to true, and will hold
  // onto the intitial inset until the animation is completed, when it will
  // re-dispatch the inset change.
  private boolean animating = false;
  // When an animation begins, android sends a WindowInset with the final
  // state of the animation. When needsSave is true, we know to capture this
  // initial WindowInset.
  private boolean needsSave = false;

  ImeSyncDeferringInsetsCallback(
      @NonNull View view, int overlayInsetTypes, int deferredInsetTypes) {
    this.overlayInsetTypes = overlayInsetTypes;
    this.deferredInsetTypes = deferredInsetTypes;
    this.view = view;
    this.animationCallback = new AnimationCallback();
    this.insetsListener = new InsetsListener();
  }

  // Add this object's event listeners to its view.
  void install() {
    view.setWindowInsetsAnimationCallback(animationCallback);
    view.setOnApplyWindowInsetsListener(insetsListener);
  }

  // Remove this object's event listeners from its view.
  void remove() {
    view.setWindowInsetsAnimationCallback(null);
    view.setOnApplyWindowInsetsListener(null);
  }

  @VisibleForTesting
  View.OnApplyWindowInsetsListener getInsetsListener() {
    return insetsListener;
  }

  @VisibleForTesting
  WindowInsetsAnimation.Callback getAnimationCallback() {
    return animationCallback;
  }

  // WindowInsetsAnimation.Callback was introduced in API level 30.  The callback
  // subclass is separated into an inner class in order to avoid warnings from
  // the Android class loader on older platforms.
  @Keep
  private class AnimationCallback extends WindowInsetsAnimation.Callback {
    AnimationCallback() {
      super(WindowInsetsAnimation.Callback.DISPATCH_MODE_CONTINUE_ON_SUBTREE);
    }

    @Override
    public void onPrepare(WindowInsetsAnimation animation) {
      if ((animation.getTypeMask() & deferredInsetTypes) != 0) {
        animating = true;
        needsSave = true;
      }
    }

    @Override
    public WindowInsets onProgress(
        WindowInsets insets, List<WindowInsetsAnimation> runningAnimations) {
      if (!animating || needsSave) {
        return insets;
      }
      boolean matching = false;
      for (WindowInsetsAnimation animation : runningAnimations) {
        if ((animation.getTypeMask() & deferredInsetTypes) != 0) {
          matching = true;
          continue;
        }
      }
      if (!matching) {
        return insets;
      }
      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 + reLu, which causes the
      // IME inset to be overlaid with any bars present.
      Insets newImeInsets =
          Insets.of(
              0,
              0,
              0,
              Math.max(
                  insets.getInsets(deferredInsetTypes).bottom
                      - insets.getInsets(overlayInsetTypes).bottom,
                  0));
      builder.setInsets(deferredInsetTypes, newImeInsets);
      // 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;
    }

    @Override
    public void onEnd(WindowInsetsAnimation animation) {
      if (animating && (animation.getTypeMask() & deferredInsetTypes) != 0) {
        // If we deferred the IME insets and an IME animation has finished, we need to reset
        // the flags
        animating = false;

        // And finally dispatch the deferred insets to the view now.
        // Ideally we would just call view.requestApplyInsets() and let the normal dispatch
        // cycle happen, but this happens too late resulting in a visual flicker.
        // Instead we manually dispatch the most recent WindowInsets to the view.
        if (lastWindowInsets != null && view != null) {
          view.dispatchApplyWindowInsets(lastWindowInsets);
        }
      }
    }
  }

  private class InsetsListener implements View.OnApplyWindowInsetsListener {
    @Override
    public WindowInsets onApplyWindowInsets(View view, WindowInsets windowInsets) {
      ImeSyncDeferringInsetsCallback.this.view = view;
      if (needsSave) {
        // Store the view and insets for us in onEnd() below. This captured inset
        // is not part of the animation and instead, represents the final state
        // of the inset after the animation is completed. Thus, we defer the processing
        // of this WindowInset until the animation completes.
        lastWindowInsets = windowInsets;
        needsSave = false;
      }
      if (animating) {
        // 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);
    }
  }
}