Avoid IME restart for configChanges

Handle onConfigurationChanged() in order to prevent restarting
InputMethodService everytime. We introduce a new API attribute
"configChanges" in InputMethod(attrs.xml) which when declared
by IME, will be responsible for handling mentioned
configuration changes.

This CL re-introduces [1] with fix: Use new Configuration instance for
IMS#mLastKnownConfig and also handle followup comments.

[1] Ib94fddadb0dae648cf73a4c1642e51edebd19f50

Note: this change has no impact for devices not using DisplayAreas.

Bug: 167948419
Test: atest InputMethodServiceTest
    Manually:
      1. Patch Ie91e7a8e06b80864ef9409031e8543858552d70d to use dual
         display area.
      2. Open applications with editors on both display areas.
      3. Attach a debug point for IMS#onConfigurationChanged().
      4. Make sure IMS#resetStateForNewConfiguration() is not called
         when IME moves between these two identical DisplayAreas
    Also verify that bug 182604598 don't happen.

Change-Id: I43b6b80cdb35410554412ee1d3b0917ee3198272

1 files changed, 102 insertions, 0 deletions

diff --git a/core/java/android/inputmethodservice/ImsConfigurationTracker.java b/core/java/android/inputmethodservice/ImsConfigurationTracker.java
new file mode 100644
index 000000000000..3c788884371b
--- /dev/null
+++ b/core/java/android/inputmethodservice/ImsConfigurationTracker.java
@@ -0,0 +1,102 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.inputmethodservice;
+
+import android.annotation.MainThread;
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.content.res.Configuration;
+import android.content.res.Resources;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.util.Preconditions;
+
+/**
+ * Helper class that takes care of Configuration change behavior of {@link InputMethodService}.
+ * Note: this class is public for testing only. Never call any of it's methods for development
+ * of IMEs.
+ * @hide
+ */
+@VisibleForTesting(visibility = VisibleForTesting.Visibility.PACKAGE)
+public final class ImsConfigurationTracker {
+
+    /**
+     * A constant value that represents {@link Configuration} has changed from the last time
+     * {@link InputMethodService#onConfigurationChanged(Configuration)} was called.
+     */
+    private static final int CONFIG_CHANGED = -1;
+
+    @Nullable
+    private Configuration mLastKnownConfig = null;
+    private int mHandledConfigChanges = 0;
+    private boolean mInitialized = false;
+
+    /**
+     * Called from {@link InputMethodService.InputMethodImpl
+     * #initializeInternal(IBinder, int, IInputMethodPrivilegedOperations, int)} ()}
+     * @param handledConfigChanges Configuration changes declared handled by IME
+     * {@link android.R.styleable#InputMethod_configChanges}.
+     */
+    @MainThread
+    public void onInitialize(int handledConfigChanges) {
+        Preconditions.checkState(!mInitialized, "onInitialize can be called only once.");
+        mInitialized = true;
+        mHandledConfigChanges = handledConfigChanges;
+    }
+
+    /**
+     * Called from {@link InputMethodService.InputMethodImpl#onBindInput()}
+     */
+    @MainThread
+    public void onBindInput(@Nullable Resources resources) {
+        Preconditions.checkState(mInitialized,
+                "onBindInput can be called only after onInitialize().");
+        if (mLastKnownConfig == null && resources != null) {
+            mLastKnownConfig = new Configuration(resources.getConfiguration());
+        }
+    }
+
+    /**
+     * Dynamically set handled configChanges.
+     * Note: this method is public for testing only.
+     */
+    public void setHandledConfigChanges(int configChanges) {
+        mHandledConfigChanges = configChanges;
+    }
+
+    /**
+     * Called from {@link InputMethodService.InputMethodImpl#onConfigurationChanged(Configuration)}}
+     */
+    @MainThread
+    public void onConfigurationChanged(@NonNull Configuration newConfig,
+            @NonNull Runnable resetStateForNewConfigurationRunner) {
+        if (!mInitialized) {
+            return;
+        }
+        final int diff = mLastKnownConfig != null
+                ? mLastKnownConfig.diffPublicOnly(newConfig) : CONFIG_CHANGED;
+        // If the new config is the same as the config this Service is already running with,
+        // then don't bother calling resetStateForNewConfiguration.
+        final int unhandledDiff = (diff & ~mHandledConfigChanges);
+        if (unhandledDiff != 0) {
+            resetStateForNewConfigurationRunner.run();
+        }
+        if (diff != 0) {
+            mLastKnownConfig = new Configuration(newConfig);
+        }
+    }
+}