blundell · August 29, 2015 14:03 · Jul 14, 2014 · Jul 13, 2014 · Jul 13, 2014 · Jul 13, 2014
diff --git a/WatchFaceLifecycle.java b/WatchFaceLifecycle.java
@@ -97,7 +97,14 @@ public void onDisplayRemoved(int displayId) {
 
         @Override
         public void onDisplayChanged(int displayId) {
-            switch (displayManager.getDisplay(displayId).getState()) {
+            Display display = displayManager.getDisplay(displayId);
+            if(display == null) {
+                // No display found for this ID, treating this as an onScreenOff() but you could remove this line
+                // and swallow this exception quietly. What circumstance means 'there is no display for this id'?
+                listener.onScreenOff();
+                return;
+            }
+            switch (display.getState()) {
                 case Display.STATE_DOZING:
                     listener.onScreenDim();
                     break;

diff --git a/WatchFaceLifecycle.java b/WatchFaceLifecycle.java
@@ -12,7 +12,7 @@
  * Prefer composition over inheritance
  * <p/>
  * This was created by Paul Blundell based on the Unofficial Base WatchFace Activity by Tavon Gatling
- * 
+ * https://gist.github.com/blundell/bba18a128214d5fa1250
  * https://gist.github.com/kentarosu/52fb21eb92181716b0ce
  * http://gist.github.com/PomepuyN/cdd821eca163a3279de2.
  */

diff --git a/WatchFaceLifecycle-ExampleActivity.java b/WatchFaceLifecycle-ExampleActivity.java
@@ -7,7 +7,7 @@ protected void onCreate(Bundle savedInstanceState) {
         WatchFaceLifecycle.attach(this, savedInstanceState, this);
     }
 
-        @Override
+    @Override
     public void onScreenDim() {
 
     }

diff --git a/ZExampleActivity.java → WatchFaceLifecycle-ExampleActivity.java b/ZExampleActivity.java → WatchFaceLifecycle-ExampleActivity.java
diff --git a/ExampleActivity.java → ZExampleActivity.java b/ExampleActivity.java → ZExampleActivity.java
diff --git a/ExampleActivity.java b/ExampleActivity.java
@@ -1,4 +1,4 @@
-public class ExampleAtivity extends Activity implements WatchFaceLifecycle.Listener {
+public class ExampleActivity extends Activity implements WatchFaceLifecycle.Listener {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {

diff --git a/ExampleActivity.java b/ExampleActivity.java
@@ -1,4 +1,4 @@
-public class Exampletivity extends Activity implements WatchFaceLifecycle.Listener {
+public class ExampleAtivity extends Activity implements WatchFaceLifecycle.Listener {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {

diff --git a/ExampleActivity.java b/ExampleActivity.java
@@ -1,4 +1,4 @@
-public class MyExampletivity extends Activity implements WatchFaceLifecycle.Listener {
+public class Exampletivity extends Activity implements WatchFaceLifecycle.Listener {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {

diff --git a/ExampleActivity.java b/ExampleActivity.java
@@ -1,4 +1,4 @@
-public class MyActivity extends Activity implements WatchFaceLifecycle.Listener {
+public class MyExampletivity extends Activity implements WatchFaceLifecycle.Listener {
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {

diff --git a/ExampleActivity → ExampleActivity.java b/ExampleActivity → ExampleActivity.java
diff --git a/Example Activity → ExampleActivity b/Example Activity → ExampleActivity
@@ -1,5 +1,3 @@
-Example use:
-
 public class MyActivity extends Activity implements WatchFaceLifecycle.Listener {
 
     @Override

diff --git a/WatchFaceLifecycle → WatchFaceLifecycle.java b/WatchFaceLifecycle → WatchFaceLifecycle.java
diff --git a/Example Activity b/Example Activity
@@ -0,0 +1,31 @@
+Example use:
+
+public class MyActivity extends Activity implements WatchFaceLifecycle.Listener {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_my_layout);
+        WatchFaceLifecycle.attach(this, savedInstanceState, this);
+    }
+
+        @Override
+    public void onScreenDim() {
+
+    }
+
+    @Override
+    public void onScreenAwake() {
+
+    }
+
+    @Override
+    public void onWatchFaceRemoved() {
+
+    }
+
+    @Override
+    public void onScreenOff() {
+
+    }
+}
diff --git a/WatchFaceLifecycle b/WatchFaceLifecycle
@@ -0,0 +1,136 @@
+import android.app.Activity;
+import android.app.Application;
+import android.content.Context;
+import android.hardware.display.DisplayManager;
+import android.os.Bundle;
+import android.view.Display;
+
+/**
+ * A listener for watch faces that have callbacks for the various screen states (dim, awake, and off)
+ * as well as a callback for when the watch face is removed.
+ * <p/>
+ * Prefer composition over inheritance
+ * <p/>
+ * This was created by Paul Blundell based on the Unofficial Base WatchFace Activity by Tavon Gatling
+ * 
+ * https://gist.github.com/kentarosu/52fb21eb92181716b0ce
+ * http://gist.github.com/PomepuyN/cdd821eca163a3279de2.
+ */
+public class WatchFaceLifecycle {
+
+    interface Listener {
+        /**
+         * Used to detect when the watch is dimming.<br/>
+         * Remember to make gray-scale versions of your watch face so they won't burn
+         * and drain battery unnecessarily.
+         */
+        void onScreenDim();
+
+        /**
+         * Used to detect when the watch is not in a dimmed state.<br/>
+         * This does not handle when returning "home" from a different activity/application.
+         */
+        void onScreenAwake();
+
+        /**
+         * Used to detect when a watch face is being removed (switched).<br/>
+         * You can either do what you need here, or simply override {@code onDestroy()}.
+         */
+        void onWatchFaceRemoved();
+
+        /**
+         * When the screen is OFF due to "Always-On" being disabled.
+         */
+        void onScreenOff();
+
+    }
+
+    private WatchFaceLifecycle() {
+    }
+
+    public static void attach(Activity activity, Bundle savedInstanceState, Listener listener) {
+        RealWatchFaceLifecycleCallbacks.newInstance(activity, savedInstanceState, listener);
+    }
+
+    private static class RealWatchFaceLifecycleCallbacks implements Application.ActivityLifecycleCallbacks, DisplayManager.DisplayListener {
+
+        private final DisplayManager displayManager;
+        private final Listener listener;
+
+        public RealWatchFaceLifecycleCallbacks(DisplayManager displayManager, Listener listener) {
+            this.displayManager = displayManager;
+            this.listener = listener;
+        }
+
+        private static void newInstance(Activity activity, Bundle savedInstanceState, Listener listener) {
+            DisplayManager displayManager = (DisplayManager) activity.getSystemService(Context.DISPLAY_SERVICE);
+            RealWatchFaceLifecycleCallbacks watchFace = new RealWatchFaceLifecycleCallbacks(displayManager, listener);
+            activity.getApplication().registerActivityLifecycleCallbacks(watchFace);
+            watchFace.onActivityCreated(activity, savedInstanceState);
+        }
+
+        @Override
+        public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
+            //  Set up the display manager and register a listener (this activity).
+            displayManager.registerDisplayListener(this, null);
+        }
+
+        @Override
+        public void onActivityStarted(Activity activity) {
+            // not used
+        }
+
+        @Override
+        public void onActivityResumed(Activity activity) {
+            // not used
+        }
+
+        @Override
+        public void onDisplayAdded(int displayId) {
+            //  In testing, this was never called, so the listener for this was removed.
+        }
+
+        @Override
+        public void onDisplayRemoved(int displayId) {
+            listener.onWatchFaceRemoved();
+        }
+
+        @Override
+        public void onDisplayChanged(int displayId) {
+            switch (displayManager.getDisplay(displayId).getState()) {
+                case Display.STATE_DOZING:
+                    listener.onScreenDim();
+                    break;
+                case Display.STATE_OFF:
+                    listener.onScreenOff();
+                    break;
+                default:
+                    //  Not really sure what to so about Display.STATE_UNKNOWN, so we'll treat it as if the screen is normal.
+                    listener.onScreenAwake();
+                    break;
+            }
+        }
+
+        @Override
+        public void onActivityPaused(Activity activity) {
+            // not used
+        }
+
+        @Override
+        public void onActivityStopped(Activity activity) {
+            // not used
+        }
+
+        @Override
+        public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
+            // not used
+        }
+
+        @Override
+        public void onActivityDestroyed(Activity activity) {
+            activity.getApplication().unregisterActivityLifecycleCallbacks(this);
+            //  Unregister the listener. If you don't, even after the watch face is gone, it will still accept your callbacks.
+            displayManager.unregisterDisplayListener(this);
+        }
+    }
+}