android: Improve ActivityStatus and add ChromiumActivity.

base/android/java/src/org/chromium/base/ActivityStatus.java

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.base;
 
+import android.app.Activity;
 import android.os.Looper;
 
 import java.util.ArrayList;
 
 /**
  * Provides information about the parent activity's status.
  */
 public class ActivityStatus {
+
+    // Constants matching activity states reported to
+    // StateListener.onStateChange

[Philippe, 2012/12/04 16:12:42]

Nit: I think this can fit on the line above. Generally we tend to put as much
content as possible on lines (100 char limit in Java). I don't know if your
editor can do this automatically.

[digit1, 2012/12/04 17:31:23]

Done.

+    public static final int CREATED = 1;
+    public static final int STARTED = 2;
+    public static final int RESUMED = 3;
+    public static final int PAUSED = 4;
+    public static final int STOPPED = 5;
+    public static final int DESTROYED = 6;
+
+    // Current activity, or null if none.
+    private static Activity sActivity;
+
+    // Current activity's state. This can be set to PAUSED or RESUMED
+    // even if there sActivity is null to facilite unit testing.
+    private static int sActivityState;
+
+    // Current activity instance, or null.
+    private static ActivityStatus sInstance;
+
+    // List of deprecated pause/resume listeners.

[digit1, 2012/12/04 15:45:34]

Ignore the "deprecated" here, I'll remove it.

[digit1, 2012/12/04 17:31:23]

Done.

+    private ArrayList<Listener> mListeners = new ArrayList<Listener>();

[Philippe, 2012/12/04 16:12:42]

Nit: you can make this field and the one below 'final'.

[digit1, 2012/12/04 17:31:23]

Done.

+
+    // List of state listeners.
+    private ArrayList<StateListener> mStateListeners = new ArrayList<StateListener>();
+
+    /**
+     * Must be called by the activity changes state.
+     * @param activity Current activity.
+     * @param newState New state value.
+     */
+    public static void onStateChange(Activity activity, int newState) {
+        if (newState == CREATED)
+          sActivity = activity;

[Philippe, 2012/12/04 16:12:42]

Nit: 4 space indentation here and in some other places (e.g. line 55).

[digit1, 2012/12/04 17:31:23]

Done.

+
+        sActivityState = newState;
+        getInstance().changeState(newState);
+
+        if (newState == DESTROYED)
+          sActivity = null;
+    }
+
+    private void changeState(int newState) {
+        for (StateListener listener : mStateListeners) {
+            listener.onActivityStateChange(newState);
+        }
+        if (newState == PAUSED || newState == RESUMED) {
+            boolean paused = (newState == PAUSED);
+            for (Listener listener : mListeners) {
+              listener.onActivityStatusChanged(paused);
+            }
+        }
+    }
+
+    // This interface can only be used to listen to PAUSED and RESUMED events.
     public interface Listener {

[Philippe, 2012/12/04 16:12:42]

Nit: Maybe add a comment here to say that this listener is kept for backwards
compatibility or even that it is deprecated if clients can later switch to the
StateListener change interface. Note that there is a @Deprecated annotation in
case this can be considered as deprecated.

This would help the reader understand why there are two similar listener
interfaces.

[digit1, 2012/12/04 17:31:23]

Done.

         /**
          * Called when the activity's status changes.
          * @param isPaused true if the activity is paused, false if not.
          */
         public void onActivityStatusChanged(boolean isPaused);

[digit1, 2012/12/04 15:41:55]

Note that I'm pretty sure that the Android convention is to avoid the past tense
here, i.e. this should be called "onActivityStatusChange" instead. However, I
didn't want to update this here for backwards compatibility.

     }
 
-    private boolean mIsPaused = false;
-    private ArrayList<Listener> mListeners = new ArrayList<Listener>();
-    private static ActivityStatus sActivityStatus;
-
-    private ActivityStatus() {
+    // Use this interface to listen to all state changes.
+    public interface StateListener {
+        /**
+         * Called when the activity's state changes.
+         * @param activity Current activity.

[Philippe, 2012/12/04 16:12:42]

Nit: It seems that you got rid of |activity| and |oldState| after you wrote this
comment.

[digit1, 2012/12/04 17:31:23]

Done.

+         * @param oldState Previous activity state.
+         * @param newState New activity state.
+         */
+        public void onActivityStateChange(int newState);
     }
 
     public static ActivityStatus getInstance() {
         // Can only be called on the UI thread.
         assert Looper.myLooper() == Looper.getMainLooper();
-        if (sActivityStatus == null) {
-            sActivityStatus = new ActivityStatus();
+        if (sInstance == null) {
+            sInstance = new ActivityStatus();

[Philippe, 2012/12/04 16:12:42]

Nit: as a bonus you could add a protected constructor so that clients don't
instantiate ActivityStatus without subclassing it if this class is not meant to
be used directly (needs to be confirmed though).

[digit1, 2012/12/04 17:31:23]

Done.

         }
-        return sActivityStatus;
+        return sInstance;
     }
 
     /**
      * Indicates that the parent activity was paused.
      */
     public void onPause() {
-        mIsPaused = true;
-        informAllListeners();
+       changeState(PAUSED);
     }
 
     /**
      * Indicates that the parent activity was resumed.
      */
     public void onResume() {
-        mIsPaused = false;
-        informAllListeners();
+        changeState(RESUMED);
     }
 
     /**
      * Indicates that the parent activity is currently paused.
      */
     public boolean isPaused() {
-        return mIsPaused;
+        return sActivityState == PAUSED;
     }
 
     /**
-     * Registers the given listener to receive activity status updates.
+     * Returns the current main application activity.
+     */
+    static public Activity getActivity() {

[Philippe, 2012/12/04 16:12:42]

Nit: I think 'public static' is more common.

[digit1, 2012/12/04 17:31:23]

Done.

+        return sActivity;
+    }
+
+    /**
+     * Returns the current main application activity's state.
+     */
+    static public int getState() {
+      if (sActivity == null)
+        return DESTROYED;
+      else
+        return sActivityState;
+    }
+
+    /**
+     * Registers the given (deprecated) listener to receive activity
+     * status updates. Use registerStateListener() instead.
      * @param listener Listener to receive status updates.
      */
     public void registerListener(Listener listener) {
         mListeners.add(listener);
     }
 
     /**
-     * Unregisters the given listener from receiving activity status updates.
+     * Unregisters the given deprecated listener from receiving activity
+     * status updates. Use unregisterStateListener() instead.
      * @param listener Listener that doesn't want to receive status updates.
      */
     public void unregisterListener(Listener listener) {
         mListeners.remove(listener);
     }
 
-    private void informAllListeners() {
-        for (Listener listener : mListeners) {
-            listener.onActivityStatusChanged(mIsPaused);
-        }
+    /**
+     * Registers the given listener to receive activity state changes.
+     * @param listener Listener to receive state changes.
+     */
+    public static void registerStateListener(StateListener listener) {
+        ActivityStatus status = getInstance();
+        status.mStateListeners.add(listener);
+    }
+
+    /**
+     * Unregisters the given listener from receiving activity state changes.
+     * @param listener Listener that doesn't want to receive state changes.
+     */
+    public static void unregisterStateListener(StateListener listener) {
+        ActivityStatus status = getInstance();
+        status.mStateListeners.remove(listener);
     }
 }