Notify framework to clear input connection when app is backgrounded (#35054).

shell/platform/android/BUILD.gn

@@ -407,6 +407,7 @@ action("robolectric_tests") {
     "test/io/flutter/embedding/android/FlutterActivityTest.java",
     "test/io/flutter/embedding/android/FlutterFragmentTest.java",
     "test/io/flutter/embedding/engine/FlutterEngineCacheTest.java",
+    "test/io/flutter/embedding/engine/systemchannels/TextInputChannelTest.java",
     "test/io/flutter/util/PreconditionsTest.java",
   ]
 

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

@@ -9,6 +9,7 @@
 import org.json.JSONObject;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 
 import io.flutter.Log;
@@ -222,6 +223,17 @@ public void unspecifiedAction(int inputClientId) {
     );
   }
 
+  /**
+   * Instructs Flutter to clear the current input client, which ends the text
+   * input interaction with the given input control.
+   */
+  public void onConnectionClosed(int inputClientId) {
+    channel.invokeMethod(
+        "TextInputClient.onConnectionClosed",
+        Collections.singletonList(inputClientId)
+    );
+  }
+
   /**
    * Sets the {@link TextInputMethodHandler} which receives all events and requests
    * that are parsed from the underlying platform channel.

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

@@ -5,10 +5,10 @@
 package io.flutter.plugin.editing;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 import android.text.DynamicLayout;
 import android.text.Editable;
 import android.text.Layout;
-import android.text.Layout.Directions;
 import android.text.Selection;
 import android.text.TextPaint;
 import android.view.KeyEvent;
@@ -19,37 +19,51 @@
 
 import io.flutter.embedding.engine.systemchannels.TextInputChannel;
 import io.flutter.Log;
-import io.flutter.plugin.common.ErrorLogResult;
-import io.flutter.plugin.common.MethodChannel;
 
 class InputConnectionAdaptor extends BaseInputConnection {
+    @NonNull
     private final View mFlutterView;
     private final int mClient;
+    @NonNull
     private final TextInputChannel textInputChannel;
+    @NonNull
     private final Editable mEditable;
+    @NonNull
+    private final Runnable onConnectionClosed;
     private int mBatchCount;
+    @NonNull
     private InputMethodManager mImm;
+    @NonNull
     private final Layout mLayout;
 
     @SuppressWarnings("deprecation")
     public InputConnectionAdaptor(
-        View view,
+        @NonNull View view,
         int client,
-        TextInputChannel textInputChannel,
-        Editable editable
+        @NonNull TextInputChannel textInputChannel,
+        @NonNull Editable editable,
+        @NonNull Runnable onConnectionClosed
     ) {
         super(view, true);
         mFlutterView = view;
         mClient = client;
         this.textInputChannel = textInputChannel;
         mEditable = editable;
+        this.onConnectionClosed = onConnectionClosed;
         mBatchCount = 0;
         // We create a dummy Layout with max width so that the selection
         // shifting acts as if all text were in one line.
         mLayout = new DynamicLayout(mEditable, new TextPaint(), Integer.MAX_VALUE, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0.0f, false);
         mImm = (InputMethodManager) view.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
     }
 
+    @Override
+    public void closeConnection() {
+        super.closeConnection();
+        textInputChannel.onConnectionClosed(mClient);
+        onConnectionClosed.run();
+    }
+
     // Send the current state of the editable to Flutter.
     private void updateEditingState() {
         // If the IME is in the middle of a batch edit, then wait until it completes.

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

@@ -46,6 +46,13 @@ public class TextInputPlugin {
     // target is a platform view. See the comments on lockPlatformViewInputConnection for more details.
     private boolean isInputConnectionLocked;
 
+    private final Runnable onInputConnectionClosed = new Runnable() {
+        @Override
+        public void run() {
+            clearTextInputClient();
+        }
+    };
+
     public TextInputPlugin(View view, @NonNull DartExecutor dartExecutor, @NonNull PlatformViewsController platformViewsController) {
         mView = view;
         mImm = (InputMethodManager) view.getContext().getSystemService(
@@ -219,7 +226,8 @@ public InputConnection createInputConnection(View view, EditorInfo outAttrs) {
             view,
             inputTarget.id,
             textInputChannel,
-            mEditable
+            mEditable,
+            onInputConnectionClosed
         );
         outAttrs.initialSelStart = Selection.getSelectionStart(mEditable);
         outAttrs.initialSelEnd = Selection.getSelectionEnd(mEditable);

shell/platform/android/test/io/flutter/FlutterTestSuite.java

@@ -12,6 +12,7 @@
 import io.flutter.embedding.android.FlutterActivityTest;
 import io.flutter.embedding.android.FlutterFragmentTest;
 import io.flutter.embedding.engine.FlutterEngineCacheTest;
+import io.flutter.embedding.engine.systemchannels.TextInputChannelTest;
 import io.flutter.util.PreconditionsTest;
 
 @RunWith(Suite.class)
@@ -21,7 +22,8 @@
     FlutterActivityTest.class,
     FlutterFragmentTest.class,
     // FlutterActivityAndFragmentDelegateTest.class, TODO(mklim): Fix and re-enable this
-    FlutterEngineCacheTest.class
+    FlutterEngineCacheTest.class,
+    TextInputChannelTest.class
 })
 /** Runs all of the unit tests listed in the {@code @SuiteClasses} annotation. */
 public class FlutterTestSuite {}

shell/platform/android/test/io/flutter/embedding/engine/systemchannels/TextInputChannelTest.java

@@ -0,0 +1,89 @@
+package io.flutter.embedding.engine.systemchannels;
+
+import org.hamcrest.Description;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentMatcher;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+import java.nio.ByteBuffer;
+import java.util.Collections;
+
+import io.flutter.embedding.engine.dart.DartExecutor;
+import io.flutter.plugin.common.JSONMethodCodec;
+import io.flutter.plugin.common.MethodCall;
+
+import static org.mockito.Matchers.argThat;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+@Config(manifest=Config.NONE)
+@RunWith(RobolectricTestRunner.class)
+public class TextInputChannelTest {
+  @Test
+  public void itNotifiesFrameworkWhenPlatformClosesInputConnection() {
+    // Setup test.
+    final int INPUT_CLIENT_ID = 9; // Arbitrary integer.
+    DartExecutor dartExecutor = mock(DartExecutor.class);
+
+    TextInputChannel textInputChannel = new TextInputChannel(dartExecutor);
+
+    // Execute behavior under test.
+    textInputChannel.onConnectionClosed(INPUT_CLIENT_ID);
+
+    // Verify results.
+    verify(dartExecutor, times(1)).send(
+        eq("flutter/textinput"),
+        ByteBufferMatcher.eqByteBuffer(JSONMethodCodec.INSTANCE.encodeMethodCall(
+            new MethodCall(
+                "TextInputClient.onConnectionClosed",
+                Collections.singletonList(INPUT_CLIENT_ID)
+            )
+        )),
+        eq(null)
+    );
+  }
+
+  /**
+   * Mockito matcher that compares two {@link ByteBuffer}s by resetting both buffers and then
+   * utilizing their standard {@code equals()} method.
+   * <p>
+   * This matcher will change the state of the expected and actual buffers. The exact change in
+   * state depends on where the comparison fails or succeeds.
+   */
+  static class ByteBufferMatcher extends ArgumentMatcher<ByteBuffer> {
+
+    static ByteBuffer eqByteBuffer(ByteBuffer expected) {
+      return argThat(new ByteBufferMatcher(expected));
+    }
+
+    private ByteBuffer expected;
+
+    ByteBufferMatcher(ByteBuffer expected) {
+      this.expected = expected;
+    }
+
+    @Override
+    public boolean matches(Object argument) {
+      if (!(argument instanceof ByteBuffer)) {
+        return false;
+      }
+
+      // Reset the buffers for content comparison.
+      ((ByteBuffer) argument).position(0);
+      expected.position(0);
+
+      return expected.equals(argument);
+    }
+
+    // Implemented so that during a failure the expected value is
+    // shown in logs, rather than the name of this class.
+    @Override
+    public void describeTo(Description description) {
+      description.appendText(expected.toString());
+    }
+  }
+}