Add a LiveDataController

Bug: 137558156
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.core

Change-Id: I5c223fbeb83e3f51ddb154de4990c3e3428ba442

src/com/android/settings/core/LiveDataController.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2019 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 com.android.settings.core;
+
+import android.content.Context;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+import androidx.annotation.WorkerThread;
+import androidx.fragment.app.Fragment;
+import androidx.lifecycle.MutableLiveData;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceScreen;
+
+import com.android.settings.R;
+import com.android.settingslib.utils.ThreadUtils;
+
+/**
+ * This controller is targeted at the time consuming-bound controller.
+ */
+public abstract class LiveDataController extends BasePreferenceController {
+    @VisibleForTesting
+    protected CharSequence mSummary;
+
+    private Preference mPreference;
+    private MutableLiveData<CharSequence> mData;
+
+
+    public LiveDataController(Context context, String preferenceKey) {
+        super(context, preferenceKey);
+        mData = new MutableLiveData<>();
+        mSummary = context.getText(R.string.summary_placeholder);
+    }
+
+    /**
+     * Initialize controller as live data controller and
+     * execute the background task for retrieving the summary text right away.
+     * @param fragment the owner of the live data observer.
+     */
+    public void initLifeCycleOwner(@NonNull Fragment fragment) {
+        mData.observe(fragment, str -> {
+            mSummary = str;
+            refreshSummary(mPreference);
+        });
+        ThreadUtils.postOnBackgroundThread(() -> {
+            mData.postValue(getSummaryTextInBackground());
+        });
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+        mPreference = screen.findPreference(getPreferenceKey());
+    }
+
+    @Override
+    public CharSequence getSummary() {
+        return mSummary;
+    }
+
+    /**
+     * Execute the time consuming work.
+     */
+    @WorkerThread
+    protected abstract CharSequence getSummaryTextInBackground();
+}