Add the Loader and supporting classes.

Loaders are designed to make it easier to manage
asynchronously loading data.

Change-Id: I948db08c721411e94fca071dc6fb4db2b83ea4d6

1 files changed, 86 insertions, 0 deletions

diff --git a/core/java/android/content/AsyncTaskLoader.java b/core/java/android/content/AsyncTaskLoader.java
new file mode 100644
index 000000000000..52a1b352f378
--- /dev/null
+++ b/core/java/android/content/AsyncTaskLoader.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2010 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 android.content;
+
+import android.os.AsyncTask;
+
+/**
+ * Abstract Loader that provides an {@link AsyncTask} to do the work.
+ * 
+ * @param <D> the data type to be loaded.
+ */
+public abstract class AsyncTaskLoader<D> extends Loader<D> {
+    final class LoadTask extends AsyncTask<Void, Void, D> {
+        /* Runs on a worker thread */
+        @Override
+        protected D doInBackground(Void... params) {
+            return AsyncTaskLoader.this.loadInBackground();
+        }
+
+        /* Runs on the UI thread */
+        @Override
+        protected void onPostExecute(D data) {
+            AsyncTaskLoader.this.dispatchOnLoadComplete(data);
+        }
+    }
+
+    LoadTask mTask;
+
+    public AsyncTaskLoader(Context context) {
+        super(context);
+    }
+
+    /**
+     * Force an asynchronous load. Unlike {@link #startLoading()} this will ignore a previously
+     * loaded data set and load a new one.
+     */
+    @Override
+    public void forceLoad() {
+        mTask = new LoadTask();
+        mTask.execute((Void[]) null);
+    }
+
+    /**
+     * Attempt to cancel the current load task. See {@link AsyncTask#cancel(boolean)}
+     * for more info.
+     *
+     * @return <tt>false</tt> if the task could not be canceled,
+     *         typically because it has already completed normally, or
+     *         because {@link #startLoading()} hasn't been called, and
+     *         <tt>true</tt> otherwise
+     */
+    public boolean cancelLoad() {
+        if (mTask != null) {
+            return mTask.cancel(false);
+        }
+        return false;
+    }
+    
+    void dispatchOnLoadComplete(D data) {
+        mTask = null;
+        deliverResult(data);
+    }
+
+    /**
+     * Called on a worker thread to perform the actual load. Implementations should not deliver the
+     * results directly, but should return them from this method and deliver them from
+     * {@link #onPostExecute()}
+     *
+     * @return the result of the load
+     */
+    public abstract D loadInBackground();
+}