Support automatic cancellation of Loaders.

Change-Id: I18d3f49e413f48fcdd519d15e99c238ad54d35b9

Author: Jeff Brown

api/current.txt

@@ -4660,10 +4660,9 @@ package android.content {
 
   public abstract class AsyncTaskLoader extends android.content.Loader {
     ctor public AsyncTaskLoader(android.content.Context);
-    method public boolean cancelLoad();
-    method protected boolean isLoadInBackgroundCanceled();
+    method public void cancelLoadInBackground();
+    method public boolean isLoadInBackgroundCanceled();
     method public abstract D loadInBackground();
-    method protected void onCancelLoadInBackground();
     method public void onCanceled(D);
     method protected D onLoadInBackground();
     method public void setUpdateThrottle(long);
@@ -5754,7 +5753,9 @@ package android.content {
   public class Loader {
     ctor public Loader(android.content.Context);
     method public void abandon();
+    method public boolean cancelLoad();
     method public java.lang.String dataToString(D);
+    method public void deliverCancellation();
     method public void deliverResult(D);
     method public void dump(java.lang.String, java.io.FileDescriptor, java.io.PrintWriter, java.lang.String[]);
     method public void forceLoad();
@@ -5764,23 +5765,30 @@ package android.content {
     method public boolean isReset();
     method public boolean isStarted();
     method protected void onAbandon();
+    method protected boolean onCancelLoad();
     method public void onContentChanged();
     method protected void onForceLoad();
     method protected void onReset();
     method protected void onStartLoading();
     method protected void onStopLoading();
     method public void registerListener(int, android.content.Loader.OnLoadCompleteListener<D>);
+    method public void registerOnLoadCanceledListener(android.content.Loader.OnLoadCanceledListener<D>);
     method public void reset();
     method public final void startLoading();
     method public void stopLoading();
     method public boolean takeContentChanged();
     method public void unregisterListener(android.content.Loader.OnLoadCompleteListener<D>);
+    method public void unregisterOnLoadCanceledListener(android.content.Loader.OnLoadCanceledListener<D>);
   }
 
   public final class Loader.ForceLoadContentObserver extends android.database.ContentObserver {
     ctor public Loader.ForceLoadContentObserver();
   }
 
+  public static abstract interface Loader.OnLoadCanceledListener {
+    method public abstract void onLoadCanceled(android.content.Loader<D>);
+  }
+
   public static abstract interface Loader.OnLoadCompleteListener {
     method public abstract void onLoadComplete(android.content.Loader<D>, D);
   }

core/java/android/app/LoaderManager.java

@@ -17,6 +17,7 @@
 package android.app;
 
 import android.content.Loader;
+import android.content.Loader.OnLoadCanceledListener;
 import android.os.Bundle;
 import android.util.DebugUtils;
 import android.util.Log;
@@ -219,7 +220,8 @@ class LoaderManagerImpl extends LoaderManager {
 
     boolean mCreatingLoader;
 
-    final class LoaderInfo implements Loader.OnLoadCompleteListener<Object> {
+    final class LoaderInfo implements Loader.OnLoadCompleteListener<Object>,
+            Loader.OnLoadCanceledListener<Object> {
         final int mId;
         final Bundle mArgs;
         LoaderManager.LoaderCallbacks<Object> mCallbacks;
@@ -271,6 +273,7 @@ void start() {
                 }
                 if (!mListenerRegistered) {
                     mLoader.registerListener(mId, this);
+                    mLoader.registerOnLoadCanceledListener(this);
                     mListenerRegistered = true;
                 }
                 mLoader.startLoading();
@@ -329,11 +332,21 @@ void stop() {
                     // Let the loader know we're done with it
                     mListenerRegistered = false;
                     mLoader.unregisterListener(this);
+                    mLoader.unregisterOnLoadCanceledListener(this);
                     mLoader.stopLoading();
                 }
             }
         }
-        
+
+        void cancel() {
+            if (DEBUG) Log.v(TAG, "  Canceling: " + this);
+            if (mStarted && mLoader != null && mListenerRegistered) {
+                if (!mLoader.cancelLoad()) {
+                    onLoadCanceled(mLoader);
+                }
+            }
+        }
+
         void destroy() {
             if (DEBUG) Log.v(TAG, "  Destroying: " + this);
             mDestroyed = true;
@@ -361,15 +374,46 @@ void destroy() {
                 if (mListenerRegistered) {
                     mListenerRegistered = false;
                     mLoader.unregisterListener(this);
+                    mLoader.unregisterOnLoadCanceledListener(this);
                 }
                 mLoader.reset();
             }
             if (mPendingLoader != null) {
                 mPendingLoader.destroy();
             }
         }
-        
-        @Override public void onLoadComplete(Loader<Object> loader, Object data) {
+
+        @Override
+        public void onLoadCanceled(Loader<Object> loader) {
+            if (DEBUG) Log.v(TAG, "onLoadCanceled: " + this);
+
+            if (mDestroyed) {
+                if (DEBUG) Log.v(TAG, "  Ignoring load canceled -- destroyed");
+                return;
+            }
+
+            if (mLoaders.get(mId) != this) {
+                // This cancellation message is not coming from the current active loader.
+                // We don't care about it.
+                if (DEBUG) Log.v(TAG, "  Ignoring load canceled -- not active");
+                return;
+            }
+
+            LoaderInfo pending = mPendingLoader;
+            if (pending != null) {
+                // There is a new request pending and we were just
+                // waiting for the old one to cancel or complete before starting
+                // it.  So now it is time, switch over to the new loader.
+                if (DEBUG) Log.v(TAG, "  Switching to pending loader: " + pending);
+                mPendingLoader = null;
+                mLoaders.put(mId, null);
+                destroy();
+                installLoader(pending);
+            }
+        }
+
+        @Override
+        public void onLoadComplete(Loader<Object> loader, Object data) {
             if (DEBUG) Log.v(TAG, "onLoadComplete: " + this);
 
             if (mDestroyed) {
@@ -632,7 +676,9 @@ public <D> Loader<D> restartLoader(int id, Bundle args, LoaderManager.LoaderCall
                     } else {
                         // Now we have three active loaders... we'll queue
                         // up this request to be processed once one of the other loaders
-                        // finishes.
+                        // finishes or is canceled.
+                        if (DEBUG) Log.v(TAG, "  Current loader is running; attempting to cancel");
+                        info.cancel();
                         if (info.mPendingLoader != null) {
                             if (DEBUG) Log.v(TAG, "  Removing pending loader: " + info.mPendingLoader);
                             info.mPendingLoader.destroy();