Close connection on keyboard close (flutter/engine#41500)

Fix:
- https://github.com/flutter/flutter/issues/123523
- https://github.com/flutter/flutter/issues/124890

### Before this patch:

https://user-images.githubusercontent.com/30322203/228413196-29c57bb0-3220-495b-9e73-f58777de440f.mp4

### After this patch:

https://user-images.githubusercontent.com/30322203/228413249-fc06f49d-6579-4476-9788-90f12a53b8c3.mp4

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java

@@ -367,6 +367,14 @@ public class TextInputChannel {
         "TextInputClient.performPrivateCommand", Arrays.asList(inputClientId, json));
   }
 
+  /** Instructs Flutter to execute a "onConnectionClosed" action. */
+  public void onConnectionClosed(int inputClientId) {
+    Log.v(TAG, "Sending 'onConnectionClosed' message.");
+    channel.invokeMethod(
+        "TextInputClient.onConnectionClosed",
+        Arrays.asList(inputClientId, "TextInputClient.onConnectionClosed"));
+  }
+
   /**
    * Sets the {@link TextInputMethodHandler} which receives all events and requests that are parsed
    * from the underlying platform channel.

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

@@ -14,6 +14,8 @@ import androidx.annotation.Keep;
 import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 import androidx.annotation.VisibleForTesting;
+import androidx.core.view.ViewCompat;
+import androidx.core.view.WindowInsetsCompat;
 import java.util.List;
 
 // Loosely based off of
@@ -41,7 +43,9 @@ import java.util.List;
 // 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
+
+// This class should have "package private" visibility cause it's called from TextInputPlugin.
+@VisibleForTesting(otherwise = VisibleForTesting.PACKAGE_PRIVATE)
 @TargetApi(30)
 @RequiresApi(30)
 @SuppressLint({"NewApi", "Override"})
@@ -54,6 +58,7 @@ class ImeSyncDeferringInsetsCallback {
   private WindowInsets lastWindowInsets;
   private AnimationCallback animationCallback;
   private InsetsListener insetsListener;
+  private ImeVisibleListener imeVisibleListener;
 
   // True when an animation that matches deferredInsetTypes is active.
   //
@@ -88,6 +93,11 @@ class ImeSyncDeferringInsetsCallback {
     view.setOnApplyWindowInsetsListener(null);
   }
 
+  // Set a listener to be notified when the IME visibility changes.
+  void setImeVisibleListener(ImeVisibleListener imeVisibleListener) {
+    this.imeVisibleListener = imeVisibleListener;
+  }
+
   @VisibleForTesting
   View.OnApplyWindowInsetsListener getInsetsListener() {
     return insetsListener;
@@ -98,6 +108,11 @@ class ImeSyncDeferringInsetsCallback {
     return animationCallback;
   }
 
+  @VisibleForTesting
+  ImeVisibleListener getImeVisibleListener() {
+    return imeVisibleListener;
+  }
+
   // 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.
@@ -115,6 +130,20 @@ class ImeSyncDeferringInsetsCallback {
       }
     }
 
+    @NonNull
+    @Override
+    public WindowInsetsAnimation.Bounds onStart(
+        @NonNull WindowInsetsAnimation animation, @NonNull WindowInsetsAnimation.Bounds bounds) {
+      // Observe changes to software keyboard visibility and notify listener when animation start.
+      // See https://developer.android.com/develop/ui/views/layout/sw-keyboard.
+      WindowInsetsCompat insets = ViewCompat.getRootWindowInsets(view);
+      if (insets != null && imeVisibleListener != null) {
+        boolean imeVisible = insets.isVisible(WindowInsetsCompat.Type.ime());
+        imeVisibleListener.onImeVisibleChanged(imeVisible);
+      }
+      return super.onStart(animation, bounds);
+    }
+
     @Override
     public WindowInsets onProgress(
         WindowInsets insets, List<WindowInsetsAnimation> runningAnimations) {
@@ -199,4 +228,9 @@ class ImeSyncDeferringInsetsCallback {
       return view.onApplyWindowInsets(windowInsets);
     }
   }
+
+  // Listener for IME visibility changes.
+  public interface ImeVisibleListener {
+    void onImeVisibleChanged(boolean visible);
+  }
 }

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

@@ -94,6 +94,17 @@ public class TextInputPlugin implements ListenableEditingState.EditingStateWatch
               WindowInsets.Type.ime() // Deferred, insets that will animate
               );
       imeSyncCallback.install();
+
+      // When the IME is hidden, we need to notify the framework that close connection.
+      imeSyncCallback.setImeVisibleListener(
+          new ImeSyncDeferringInsetsCallback.ImeVisibleListener() {
+            @Override
+            public void onImeVisibleChanged(boolean visible) {
+              if (!visible) {
+                onConnectionClosed();
+              }
+            }
+          });
     }
 
     this.textInputChannel = textInputChannel;
@@ -838,4 +849,8 @@ public class TextInputPlugin implements ListenableEditingState.EditingStateWatch
     textInputChannel.updateEditingStateWithTag(inputTarget.id, editingValues);
   }
   // -------- End: Autofill -------
+
+  public void onConnectionClosed() {
+    textInputChannel.onConnectionClosed(inputTarget.id);
+  }
 }

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

@@ -2118,6 +2118,19 @@ public class TextInputPluginTest {
     assertEquals(0, viewportMetricsCaptor.getValue().viewInsetTop);
   }
 
+  @Test
+  @TargetApi(30)
+  @Config(sdk = 30)
+  public void onConnectionClosed_imeInvisible() {
+    View testView = new View(ctx);
+    TextInputChannel textInputChannel = spy(new TextInputChannel(mock(DartExecutor.class)));
+    TextInputPlugin textInputPlugin =
+        new TextInputPlugin(testView, textInputChannel, mock(PlatformViewsController.class));
+    ImeSyncDeferringInsetsCallback imeSyncCallback = textInputPlugin.getImeSyncCallback();
+    imeSyncCallback.getImeVisibleListener().onImeVisibleChanged(false);
+    verify(textInputChannel, times(1)).onConnectionClosed(anyInt());
+  }
+
   interface EventHandler {
     void sendAppPrivateCommand(View view, String action, Bundle data);
   }