1 files changed, 144 insertions, 0 deletions
diff --git a/packages/DocumentsUI/src/com/android/documentsui/UriDerivativeLoader.java b/packages/DocumentsUI/src/com/android/documentsui/UriDerivativeLoader.java
new file mode 100644
index 0000000..1b88af4
--- /dev/null
+++ b/packages/DocumentsUI/src/com/android/documentsui/UriDerivativeLoader.java
@@ -0,0 +1,144 @@
+/*
+ * Copyright (C) 2013 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.documentsui;
+
+import android.content.AsyncTaskLoader;
+import android.content.Context;
+import android.database.ContentObserver;
+import android.net.Uri;
+import android.os.CancellationSignal;
+import android.os.OperationCanceledException;
+
+/**
+ * Loader that derives its data from a Uri. Watches for {@link ContentObserver}
+ * changes while started, manages {@link CancellationSignal}, and caches
+ * returned results.
+ */
+public abstract class UriDerivativeLoader<T> extends AsyncTaskLoader<T> {
+    private final ForceLoadContentObserver mObserver;
+    private boolean mObserving;
+
+    private final Uri mUri;
+
+    private T mResult;
+    private CancellationSignal mCancellationSignal;
+
+    @Override
+    public final T loadInBackground() {
+        synchronized (this) {
+            if (isLoadInBackgroundCanceled()) {
+                throw new OperationCanceledException();
+            }
+            mCancellationSignal = new CancellationSignal();
+        }
+        try {
+            return loadInBackground(mUri, mCancellationSignal);
+        } finally {
+            synchronized (this) {
+                mCancellationSignal = null;
+            }
+        }
+    }
+
+    public abstract T loadInBackground(Uri uri, CancellationSignal signal);
+
+    @Override
+    public void cancelLoadInBackground() {
+        super.cancelLoadInBackground();
+
+        synchronized (this) {
+            if (mCancellationSignal != null) {
+                mCancellationSignal.cancel();
+            }
+        }
+    }
+
+    @Override
+    public void deliverResult(T result) {
+        if (isReset()) {
+            closeQuietly(result);
+            return;
+        }
+        T oldResult = mResult;
+        mResult = result;
+
+        if (isStarted()) {
+            super.deliverResult(result);
+        }
+
+        if (oldResult != null && oldResult != result) {
+            closeQuietly(oldResult);
+        }
+    }
+
+    public UriDerivativeLoader(Context context, Uri uri) {
+        super(context);
+        mObserver = new ForceLoadContentObserver();
+        mUri = uri;
+    }
+
+    @Override
+    protected void onStartLoading() {
+        if (!mObserving) {
+            getContext().getContentResolver().registerContentObserver(mUri, false, mObserver);
+            mObserving = true;
+        }
+        if (mResult != null) {
+            deliverResult(mResult);
+        }
+        if (takeContentChanged() || mResult == null) {
+            forceLoad();
+        }
+    }
+
+    @Override
+    protected void onStopLoading() {
+        cancelLoad();
+    }
+
+    @Override
+    public void onCanceled(T result) {
+        closeQuietly(result);
+    }
+
+    @Override
+    protected void onReset() {
+        super.onReset();
+
+        // Ensure the loader is stopped
+        onStopLoading();
+
+        closeQuietly(mResult);
+        mResult = null;
+
+        if (mObserving) {
+            getContext().getContentResolver().unregisterContentObserver(mObserver);
+            mObserving = false;
+        }
+    }
+
+    private void closeQuietly(T result) {
+        if (result instanceof AutoCloseable) {
+            try {
+                ((AutoCloseable) result).close();
+            } catch (RuntimeException rethrown) {
+                throw rethrown;
+            } catch (Exception ignored) {
+            }
+        }
+    }
+}