Lazy loading LauncherAppState

Separating InvarantDeviceProfile out of LauncherAppState and creating
LauncherAppState only when it is actually used

Change-Id: I2ee55f53cae01f11203f94675bb5f70c65ad2b9d
diff --git a/src/com/android/launcher3/InvariantDeviceProfile.java b/src/com/android/launcher3/InvariantDeviceProfile.java
index f63cce5..22bc162 100644
--- a/src/com/android/launcher3/InvariantDeviceProfile.java
+++ b/src/com/android/launcher3/InvariantDeviceProfile.java
@@ -29,6 +29,8 @@
 import android.view.WindowManager;
 
 import com.android.launcher3.config.FeatureFlags;
+import com.android.launcher3.util.ConfigMonitor;
+import com.android.launcher3.util.MainThreadInitializedObject;
 import com.android.launcher3.util.Thunk;
 
 import org.xmlpull.v1.XmlPullParser;
@@ -41,8 +43,12 @@
 
 public class InvariantDeviceProfile {
 
-    // This is a static that we use for the default icon size on a 4/5-inch phone
-    private static float DEFAULT_ICON_SIZE_DP = 60;
+    // We do not need any synchronization for this variable as its only written on UI thread.
+    public static final MainThreadInitializedObject<InvariantDeviceProfile> INSTANCE =
+            new MainThreadInitializedObject<>((c) -> {
+                new ConfigMonitor(c).register();
+                return new InvariantDeviceProfile(c);
+            });
 
     private static final float ICON_SIZE_DEFINED_IN_APP_DP = 48;
 
@@ -118,7 +124,7 @@
     }
 
     @TargetApi(23)
-    public InvariantDeviceProfile(Context context) {
+    private InvariantDeviceProfile(Context context) {
         WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
         Display display = wm.getDefaultDisplay();
         DisplayMetrics dm = new DisplayMetrics();
diff --git a/src/com/android/launcher3/LauncherAppState.java b/src/com/android/launcher3/LauncherAppState.java
index a46692b..5159de1 100644
--- a/src/com/android/launcher3/LauncherAppState.java
+++ b/src/com/android/launcher3/LauncherAppState.java
@@ -16,12 +16,13 @@
 
 package com.android.launcher3;
 
+import static com.android.launcher3.SettingsActivity.NOTIFICATION_BADGING;
+
 import android.content.ComponentName;
 import android.content.ContentProviderClient;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
-import android.os.Looper;
 import android.util.Log;
 
 import com.android.launcher3.compat.LauncherAppsCompat;
@@ -29,21 +30,17 @@
 import com.android.launcher3.compat.UserManagerCompat;
 import com.android.launcher3.config.FeatureFlags;
 import com.android.launcher3.notification.NotificationListener;
-import com.android.launcher3.util.ConfigMonitor;
+import com.android.launcher3.util.MainThreadInitializedObject;
 import com.android.launcher3.util.Preconditions;
 import com.android.launcher3.util.SettingsObserver;
 
-import java.util.concurrent.Callable;
-import java.util.concurrent.ExecutionException;
-
-import static com.android.launcher3.SettingsActivity.NOTIFICATION_BADGING;
-
 public class LauncherAppState {
 
     public static final String ACTION_FORCE_ROLOAD = "force-reload-launcher";
 
     // We do not need any synchronization for this variable as its only written on UI thread.
-    private static LauncherAppState INSTANCE;
+    private static final MainThreadInitializedObject<LauncherAppState> INSTANCE =
+            new MainThreadInitializedObject<>((c) -> new LauncherAppState(c));
 
     private final Context mContext;
     private final LauncherModel mModel;
@@ -53,27 +50,11 @@
     private final SettingsObserver mNotificationBadgingObserver;
 
     public static LauncherAppState getInstance(final Context context) {
-        if (INSTANCE == null) {
-            if (Looper.myLooper() == Looper.getMainLooper()) {
-                INSTANCE = new LauncherAppState(context.getApplicationContext());
-            } else {
-                try {
-                    return new MainThreadExecutor().submit(new Callable<LauncherAppState>() {
-                        @Override
-                        public LauncherAppState call() throws Exception {
-                            return LauncherAppState.getInstance(context);
-                        }
-                    }).get();
-                } catch (InterruptedException|ExecutionException e) {
-                    throw new RuntimeException(e);
-                }
-            }
-        }
-        return INSTANCE;
+        return INSTANCE.get(context);
     }
 
     public static LauncherAppState getInstanceNoCreate() {
-        return INSTANCE;
+        return INSTANCE.getNoCreate();
     }
 
     public Context getContext() {
@@ -89,7 +70,7 @@
         Preconditions.assertUIThread();
         mContext = context;
 
-        mInvariantDeviceProfile = new InvariantDeviceProfile(mContext);
+        mInvariantDeviceProfile = InvariantDeviceProfile.INSTANCE.get(mContext);
         mIconCache = new IconCache(mContext, mInvariantDeviceProfile);
         mWidgetCache = new WidgetPreviewLoader(mContext, mIconCache);
         mModel = new LauncherModel(this, mIconCache, AppFilter.newInstance(mContext));
@@ -112,7 +93,6 @@
 
         mContext.registerReceiver(mModel, filter);
         UserManagerCompat.getInstance(mContext).enableAndResetCache();
-        new ConfigMonitor(mContext).register();
 
         if (!mContext.getResources().getBoolean(R.bool.notification_badging_enabled)) {
             mNotificationBadgingObserver = null;
@@ -171,7 +151,7 @@
      * Shorthand for {@link #getInvariantDeviceProfile()}
      */
     public static InvariantDeviceProfile getIDP(Context context) {
-        return LauncherAppState.getInstance(context).getInvariantDeviceProfile();
+        return InvariantDeviceProfile.INSTANCE.get(context);
     }
 
     private static LauncherProvider getLocalProvider(Context context) {
diff --git a/src/com/android/launcher3/util/MainThreadInitializedObject.java b/src/com/android/launcher3/util/MainThreadInitializedObject.java
new file mode 100644
index 0000000..5747db1
--- /dev/null
+++ b/src/com/android/launcher3/util/MainThreadInitializedObject.java
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2018 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.launcher3.util;
+
+import android.content.Context;
+import android.os.Looper;
+
+import com.android.launcher3.MainThreadExecutor;
+
+import java.util.concurrent.ExecutionException;
+
+/**
+ * Utility class for defining singletons which are initiated on main thread.
+ */
+public class MainThreadInitializedObject<T> {
+
+    private final ObjectProvider<T> mProvider;
+    private T mValue;
+
+    public MainThreadInitializedObject(ObjectProvider<T> provider) {
+        mProvider = provider;
+    }
+
+    public T get(Context context) {
+        if (mValue == null) {
+            if (Looper.myLooper() == Looper.getMainLooper()) {
+                mValue = mProvider.get(context.getApplicationContext());
+            } else {
+                try {
+                    return new MainThreadExecutor().submit(() -> get(context)).get();
+                } catch (InterruptedException|ExecutionException e) {
+                    throw new RuntimeException(e);
+                }
+            }
+        }
+        return mValue;
+    }
+
+    public T getNoCreate() {
+        return mValue;
+    }
+
+    public interface ObjectProvider<T> {
+
+        T get(Context context);
+    }
+}