Simplify state management in the Android text editing plugin (#3769)

In particular, this avoids some unnecessary calls to InputMethodManager.restartInput
that caused noticeable lag when moving the cursor.

Fixes https://github.com/flutter/flutter/issues/9928

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

@@ -4,9 +4,11 @@
 
 package io.flutter.plugin.editing;
 
+import android.content.Context;
 import android.text.Editable;
 import android.text.Selection;
 import android.view.inputmethod.BaseInputConnection;
+import android.view.inputmethod.InputMethodManager;
 import android.view.KeyEvent;
 
 import io.flutter.plugin.common.MethodChannel;
@@ -17,63 +19,104 @@ import java.util.HashMap;
 import java.util.Map;
 
 class InputConnectionAdaptor extends BaseInputConnection {
+    private final FlutterView mFlutterView;
     private final int mClient;
-    private final TextInputPlugin mPlugin;
     private final MethodChannel mFlutterChannel;
-    private final Map<String, Object> mOutgoingState;
+    private final Editable mEditable;
+    private int mBatchCount;
+    private InputMethodManager mImm;
 
     public InputConnectionAdaptor(FlutterView view, int client,
-        TextInputPlugin plugin, MethodChannel flutterChannel) {
+        MethodChannel flutterChannel, Editable editable) {
         super(view, true);
+        mFlutterView = view;
         mClient = client;
-        mPlugin = plugin;
         mFlutterChannel = flutterChannel;
-        mOutgoingState = new HashMap<>();
+        mEditable = editable;
+        mBatchCount = 0;
+        mImm = (InputMethodManager) view.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
     }
 
+    // Send the current state of the editable to Flutter.
     private void updateEditingState() {
-        final Editable content = getEditable();
-        mOutgoingState.put("text", content.toString());
-        mOutgoingState.put("selectionBase", Selection.getSelectionStart(content));
-        mOutgoingState.put("selectionExtent", Selection.getSelectionEnd(content));
-        mOutgoingState.put("composingBase", BaseInputConnection.getComposingSpanStart(content));
-        mOutgoingState.put("composingExtent", BaseInputConnection.getComposingSpanEnd(content));
-        mFlutterChannel.invokeMethod("TextInputClient.updateEditingState", Arrays
-            .asList(mClient, mOutgoingState));
-        mPlugin.setLatestEditingState(mOutgoingState);
+        // If the IME is in the middle of a batch edit, then wait until it completes.
+        if (mBatchCount > 0)
+            return;
+
+        int selectionStart = Selection.getSelectionStart(mEditable);
+        int selectionEnd = Selection.getSelectionEnd(mEditable);
+        int composingStart = BaseInputConnection.getComposingSpanStart(mEditable);
+        int composingEnd = BaseInputConnection.getComposingSpanEnd(mEditable);
+
+        mImm.updateSelection(mFlutterView,
+                             selectionStart, selectionEnd,
+                             composingStart, composingEnd);
+
+        HashMap<Object, Object> state = new HashMap<Object, Object>();
+        state.put("text", mEditable.toString());
+        state.put("selectionBase", selectionStart);
+        state.put("selectionExtent", selectionEnd);
+        state.put("composingBase", composingStart);
+        state.put("composingExtent", composingEnd);
+        mFlutterChannel.invokeMethod("TextInputClient.updateEditingState",
+            Arrays.asList(mClient, state));
+    }
+
+    @Override
+    public Editable getEditable() {
+        return mEditable;
+    }
+
+    @Override
+    public boolean beginBatchEdit() {
+        mBatchCount++;
+        return super.beginBatchEdit();
+    }
+
+    @Override
+    public boolean endBatchEdit() {
+        boolean result = super.endBatchEdit();
+        mBatchCount--;
+        updateEditingState();
+        return result;
     }
 
     @Override
     public boolean commitText(CharSequence text, int newCursorPosition) {
-        final boolean result = super.commitText(text, newCursorPosition);
+        boolean result = super.commitText(text, newCursorPosition);
         updateEditingState();
         return result;
     }
 
     @Override
     public boolean deleteSurroundingText(int beforeLength, int afterLength) {
-        final boolean result = super.deleteSurroundingText(beforeLength, afterLength);
+        boolean result = super.deleteSurroundingText(beforeLength, afterLength);
         updateEditingState();
         return result;
     }
 
     @Override
     public boolean setComposingRegion(int start, int end) {
-        final boolean result = super.setComposingRegion(start, end);
+        boolean result = super.setComposingRegion(start, end);
         updateEditingState();
         return result;
     }
 
     @Override
     public boolean setComposingText(CharSequence text, int newCursorPosition) {
-        final boolean result = super.setComposingText(text, newCursorPosition);
+        boolean result;
+        if (text.length() == 0) {
+            result = super.commitText(text, newCursorPosition);
+        } else {
+            result = super.setComposingText(text, newCursorPosition);
+        }
         updateEditingState();
         return result;
     }
 
     @Override
     public boolean setSelection(int start, int end) {
-        final boolean result = super.setSelection(start, end);
+        boolean result = super.setSelection(start, end);
         updateEditingState();
         return result;
     }
@@ -82,26 +125,26 @@ class InputConnectionAdaptor extends BaseInputConnection {
     public boolean sendKeyEvent(KeyEvent event) {
         final boolean result = super.sendKeyEvent(event);
         if (event.getAction() == KeyEvent.ACTION_UP) {
-            // Weird special case. This method is (sometimes) called for the backspace key in 2
-            // situations:
-            // 1. There is no selection. In that case, we want to delete the previous character.
-            // 2. There is a selection. In that case, we want to delete the selection.
-            //    event.getNumber() is 0, and commitText("", 1) will do what we want.
-            if (event.getKeyCode() == KeyEvent.KEYCODE_DEL &&
-                optInt("selectionBase", -1) == optInt("selectionExtent", -1)) {
-                deleteSurroundingText(1, 0);
+            if (event.getKeyCode() == KeyEvent.KEYCODE_DEL) {
+                int selStart = Selection.getSelectionStart(mEditable);
+                int selEnd = Selection.getSelectionEnd(mEditable);
+                if (selEnd > selStart) {
+                    // Delete the selection.
+                    Selection.setSelection(mEditable, selStart);
+                    deleteSurroundingText(0, selEnd - selStart);
+                } else if (selStart > 0) {
+                    // Delete to the left of the cursor.
+                    Selection.setSelection(mEditable, selStart - 1);
+                    deleteSurroundingText(0, 1);
+                }
             } else {
-                String text = event.getNumber() == 0 ? "" : String.valueOf(event.getNumber());
-                commitText(text, 1);
+                // Enter a character.
+                commitText(String.valueOf(event.getNumber()), 1);
             }
         }
         return result;
     }
 
-    private int optInt(String key, int defaultValue) {
-        return mOutgoingState.containsKey(key) ? (Integer) mOutgoingState.get(key) : defaultValue;
-    }
-
     @Override
     public boolean performEditorAction(int actionCode) {
         // TODO(abarth): Support more actions.

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

@@ -6,7 +6,10 @@ package io.flutter.plugin.editing;
 
 import android.app.Activity;
 import android.content.Context;
+import android.text.Editable;
 import android.text.InputType;
+import android.text.Selection;
+import android.view.inputmethod.BaseInputConnection;
 import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.InputConnection;
 import android.view.inputmethod.InputMethodManager;
@@ -29,16 +32,16 @@ import org.json.JSONObject;
  */
 public class TextInputPlugin implements MethodCallHandler {
 
-    private final Activity mActivity;
     private final FlutterView mView;
+    private final InputMethodManager mImm;
     private final MethodChannel mFlutterChannel;
     private int mClient = 0;
     private JSONObject mConfiguration;
-    private JSONObject mLatestState;
+    private Editable mEditable;
 
-    public TextInputPlugin(Activity activity, FlutterView view) {
-        mActivity = activity;
+    public TextInputPlugin(FlutterView view) {
         mView = view;
+        mImm = (InputMethodManager) view.getContext().getSystemService(Context.INPUT_METHOD_SERVICE);
         mFlutterChannel = new MethodChannel(view, "flutter/textinput",
             JSONMethodCodec.INSTANCE);
         mFlutterChannel.setMethodCallHandler(this);
@@ -98,60 +101,53 @@ public class TextInputPlugin implements MethodCallHandler {
         throws JSONException {
         if (mClient == 0)
             return null;
+
         outAttrs.inputType = inputTypeFromTextInputType(mConfiguration.getString("inputType"),
             mConfiguration.optBoolean("obscureText"));
         if (!mConfiguration.isNull("actionLabel"))
           outAttrs.actionLabel = mConfiguration.getString("actionLabel");
         outAttrs.imeOptions = EditorInfo.IME_ACTION_DONE | EditorInfo.IME_FLAG_NO_FULLSCREEN;
-        InputConnectionAdaptor connection = new InputConnectionAdaptor(view, mClient, this,
-            mFlutterChannel);
-        if (mLatestState != null) {
-            int selectionBase = (Integer) mLatestState.get("selectionBase");
-            int selectionExtent = (Integer) mLatestState.get("selectionExtent");
-            outAttrs.initialSelStart = selectionBase;
-            outAttrs.initialSelEnd = selectionExtent;
-            connection.getEditable().append((String) mLatestState.get("text"));
-            connection.setSelection(Math.max(selectionBase, 0),
-                Math.max(selectionExtent, 0));
-            connection.setComposingRegion((Integer) mLatestState.get("composingBase"),
-                (Integer) mLatestState.get("composingExtent"));
-        } else {
-            outAttrs.initialSelStart = 0;
-            outAttrs.initialSelEnd = 0;
-        }
+
+        InputConnectionAdaptor connection = new InputConnectionAdaptor(view, mClient, mFlutterChannel, mEditable);
+        outAttrs.initialSelStart = Math.max(Selection.getSelectionStart(mEditable), 0);
+        outAttrs.initialSelEnd = Math.max(Selection.getSelectionEnd(mEditable), 0);
+
         return connection;
     }
 
     private void showTextInput(FlutterView view) {
-        InputMethodManager imm =
-            (InputMethodManager) mActivity.getSystemService(Context.INPUT_METHOD_SERVICE);
-        imm.showSoftInput(view, 0);
+        mImm.showSoftInput(view, 0);
     }
 
     private void hideTextInput(FlutterView view) {
-        InputMethodManager imm =
-            (InputMethodManager) mActivity.getSystemService(Context.INPUT_METHOD_SERVICE);
-        imm.hideSoftInputFromWindow(view.getApplicationWindowToken(), 0);
+        mImm.hideSoftInputFromWindow(view.getApplicationWindowToken(), 0);
     }
 
     private void setTextInputClient(FlutterView view, int client, JSONObject configuration) {
-        mLatestState = null;
         mClient = client;
         mConfiguration = configuration;
-        InputMethodManager imm =
-            (InputMethodManager) mActivity.getSystemService(Context.INPUT_METHOD_SERVICE);
-        imm.restartInput(view);
-    }
+        mEditable = Editable.Factory.getInstance().newEditable("");
 
-    private void setTextInputEditingState(FlutterView view, JSONObject state) {
-        mLatestState = state;
-        InputMethodManager imm =
-            (InputMethodManager) mActivity.getSystemService(Context.INPUT_METHOD_SERVICE);
-        imm.restartInput(view);
+        mImm.restartInput(view);
     }
 
-    void setLatestEditingState(Map<String, Object> state) {
-        mLatestState = (JSONObject) JSONUtil.wrap(state);
+    private void setTextInputEditingState(FlutterView view, JSONObject state)
+        throws JSONException {
+        if (state.getString("text").equals(mEditable.toString())) {
+            Selection.setSelection(mEditable, state.getInt("selectionBase"),
+                state.getInt("selectionExtent"));
+            mImm.updateSelection(
+                mView,
+                Math.max(Selection.getSelectionStart(mEditable), 0),
+                Math.max(Selection.getSelectionEnd(mEditable), 0),
+                BaseInputConnection.getComposingSpanStart(mEditable),
+                BaseInputConnection.getComposingSpanEnd(mEditable));
+        } else {
+            mEditable.replace(0, mEditable.length(), state.getString("text"));
+            Selection.setSelection(mEditable, state.getInt("selectionBase"),
+                state.getInt("selectionExtent"));
+            mImm.restartInput(view);
+        }
     }
 
     private void clearTextInputClient() {

shell/platform/android/io/flutter/view/FlutterView.java

@@ -174,7 +174,7 @@ public class FlutterView extends SurfaceView
             "flutter/platform", JSONMethodCodec.INSTANCE);
         flutterPlatformChannel.setMethodCallHandler(platformPlugin);
         addActivityLifecycleListener(platformPlugin);
-        mTextInputPlugin = new TextInputPlugin((Activity) getContext(), this);
+        mTextInputPlugin = new TextInputPlugin(this);
 
         setLocale(getResources().getConfiguration().locale);