COMMENT ONLY change to clarify ContentProvider documentation.
Gets a little more specific about thread behavior, and makes
pointed comments about not doing too much work in onCreate().
Change-Id: I682f0eb7d7559babee901ed26642751a6ba0a1ea
diff --git a/core/java/android/content/ContentProvider.java b/core/java/android/content/ContentProvider.java
index 5fb2aae..40108c3 100644
--- a/core/java/android/content/ContentProvider.java
+++ b/core/java/android/content/ContentProvider.java
@@ -57,6 +57,7 @@
*
* <p>The primary methods that need to be implemented are:
* <ul>
+ * <li>{@link #onCreate} which is called to initialize the provider</li>
* <li>{@link #query} which returns data to the caller</li>
* <li>{@link #insert} which inserts new data into the content provider</li>
* <li>{@link #update} which updates existing data in the content provider</li>
@@ -64,8 +65,15 @@
* <li>{@link #getType} which returns the MIME type of data in the content provider</li>
* </ul></p>
*
- * <p>This class takes care of cross process calls so subclasses don't have to worry about which
- * process a request is coming from.</p>
+ * <p class="caution">Data access methods (such as {@link #insert} and
+ * {@link #update}) may be called from many threads at once, and must be thread-safe.
+ * Other methods (such as {@link #onCreate}) are only called from the application
+ * main thread, and must avoid performing lengthy operations. See the method
+ * descriptions for their expected thread behavior.</p>
+ *
+ * <p>Requests to {@link ContentResolver} are automatically forwarded to the appropriate
+ * ContentProvider instance, so subclasses don't have to worry about the details of
+ * cross-process calls.</p>
*/
public abstract class ContentProvider implements ComponentCallbacks {
/*
@@ -81,6 +89,21 @@
private Transport mTransport = new Transport();
+ /**
+ * Construct a ContentProvider instance. Content providers must be
+ * <a href="{@docRoot}guide/topics/manifest/provider-element.html">declared
+ * in the manifest</a>, accessed with {@link ContentResolver}, and created
+ * automatically by the system, so applications usually do not create
+ * ContentProvider instances directly.
+ *
+ * <p>At construction time, the object is uninitialized, and most fields and
+ * methods are unavailable. Subclasses should initialize themselves in
+ * {@link #onCreate}, not the constructor.
+ *
+ * <p>Content providers are created on the application main thread at
+ * application launch time. The constructor must not perform lengthy
+ * operations, or application startup will be delayed.
+ */
public ContentProvider() {
}
@@ -328,8 +351,8 @@
/**
- * Retrieve the Context this provider is running in. Only available once
- * onCreate(Map icicle) has been called -- this will be null in the
+ * Retrieves the Context this provider is running in. Only available once
+ * {@link #onCreate} has been called -- this will return null in the
* constructor.
*/
public final Context getContext() {
@@ -403,23 +426,59 @@
}
/**
- * Called when the provider is being started.
+ * Implement this to initialize your content provider on startup.
+ * This method is called for all registered content providers on the
+ * application main thread at application launch time. It must not perform
+ * lengthy operations, or application startup will be delayed.
+ *
+ * <p>You should defer nontrivial initialization (such as opening,
+ * upgrading, and scanning databases) until the content provider is used
+ * (via {@link #query}, {@link #insert}, etc). Deferred initialization
+ * keeps application startup fast, avoids unnecessary work if the provider
+ * turns out not to be needed, and stops database errors (such as a full
+ * disk) from halting application launch.
+ *
+ * <p>For SQL databases, {@link android.database.sqlite.SQLiteOpenHelper}
+ * is a helpful utility class that makes it easy to manage databases,
+ * and will automatically defer opening until first use. If you do use
+ * SQLiteOpenHelper, make sure to avoid calling
+ * {@link android.database.sqlite.SQLiteOpenHelper#getReadableDatabase} or
+ * {@link android.database.sqlite.SQLiteOpenHelper#getWritableDatabase}
+ * from this method. (Instead, override
+ * {@link android.database.sqlite.SQLiteOpenHelper#onOpen} to initialize the
+ * database when it is first opened.)
*
* @return true if the provider was successfully loaded, false otherwise
*/
public abstract boolean onCreate();
+ /**
+ * {@inheritDoc}
+ * This method is always called on the application main thread, and must
+ * not perform lengthy operations.
+ *
+ * <p>The default content provider implementation does nothing.
+ * Override this method to take appropriate action.
+ * (Content providers do not usually care about things like screen
+ * orientation, but may want to know about locale changes.)
+ */
public void onConfigurationChanged(Configuration newConfig) {
}
-
+
+ /**
+ * {@inheritDoc}
+ * This method is always called on the application main thread, and must
+ * not perform lengthy operations.
+ *
+ * <p>The default content provider implementation does nothing.
+ * Subclasses may override this method to take appropriate action.
+ */
public void onLowMemory() {
}
/**
- * Receives a query request from a client in a local process, and
- * returns a Cursor. This is called internally by the {@link ContentResolver}.
- * This method can be called from multiple
- * threads, as described in
+ * Implement this to handle query requests from clients.
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
* <p>
@@ -476,11 +535,11 @@
String selection, String[] selectionArgs, String sortOrder);
/**
- * Return the MIME type of the data at the given URI. This should start with
+ * Implement this to handle requests for the MIME type of the data at the
+ * given URI. The returned MIME type should start with
* <code>vnd.android.cursor.item</code> for a single record,
* or <code>vnd.android.cursor.dir/</code> for multiple items.
- * This method can be called from multiple
- * threads, as described in
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
*
@@ -490,11 +549,10 @@
public abstract String getType(Uri uri);
/**
- * Implement this to insert a new row.
+ * Implement this to handle requests to insert a new row.
* As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
* after inserting.
- * This method can be called from multiple
- * threads, as described in
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
* @param uri The content:// URI of the insertion request.
@@ -504,12 +562,12 @@
public abstract Uri insert(Uri uri, ContentValues values);
/**
- * Implement this to insert a set of new rows, or the default implementation will
- * iterate over the values and call {@link #insert} on each of them.
+ * Override this to handle requests to insert a set of new rows, or the
+ * default implementation will iterate over the values and call
+ * {@link #insert} on each of them.
* As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
* after inserting.
- * This method can be called from multiple
- * threads, as described in
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
*
@@ -526,13 +584,12 @@
}
/**
- * A request to delete one or more rows. The selection clause is applied when performing
- * the deletion, allowing the operation to affect multiple rows in a
- * directory.
+ * Implement this to handle requests to delete one or more rows.
+ * The implementation should apply the selection clause when performing
+ * deletion, allowing the operation to affect multiple rows in a directory.
* As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyDelete()}
* after deleting.
- * This method can be called from multiple
- * threads, as described in
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
*
@@ -549,13 +606,12 @@
public abstract int delete(Uri uri, String selection, String[] selectionArgs);
/**
- * Update a content URI. All rows matching the optionally provided selection
- * will have their columns listed as the keys in the values map with the
- * values of those keys.
+ * Implement this to update one or more rows.
+ * The implementation should update all rows matching the selection
+ * to set the columns according to the provided values map.
* As a courtesy, call {@link ContentResolver#notifyChange(android.net.Uri ,android.database.ContentObserver) notifyChange()}
* after updating.
- * This method can be called from multiple
- * threads, as described in
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
*
@@ -570,18 +626,15 @@
String[] selectionArgs);
/**
- * Open a file blob associated with a content URI.
- * This method can be called from multiple
- * threads, as described in
+ * Override this to open a file blob associated with a content URI.
+ * The default implementation always throws {@link FileNotFoundException}.
+ * This method can be called from multiple threads, as described in
* <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
* Processes and Threads</a>.
- *
- * <p>Returns a
- * ParcelFileDescriptor, from which you can obtain a
- * {@link java.io.FileDescriptor} for use with
- * {@link java.io.FileInputStream}, {@link java.io.FileOutputStream}, etc.
- * This can be used to store large data (such as an image) associated with
- * a particular piece of content.
+ *
+ * <p>Returns a ParcelFileDescriptor, which is returned directly to the
+ * caller. This way large data (such as images and documents) can be
+ * returned without copying the content.
*
* <p>The returned ParcelFileDescriptor is owned by the caller, so it is
* their responsibility to close it when done. That is, the implementation
@@ -599,31 +652,35 @@
* no file associated with the given URI or the mode is invalid.
* @throws SecurityException Throws SecurityException if the caller does
* not have permission to access the file.
- *
+ *
* @see #openAssetFile(Uri, String)
* @see #openFileHelper(Uri, String)
- */
+ */
public ParcelFileDescriptor openFile(Uri uri, String mode)
throws FileNotFoundException {
throw new FileNotFoundException("No files supported by provider at "
+ uri);
}
-
+
/**
* This is like {@link #openFile}, but can be implemented by providers
* that need to be able to return sub-sections of files, often assets
- * inside of their .apk. Note that when implementing this your clients
- * must be able to deal with such files, either directly with
- * {@link ContentResolver#openAssetFileDescriptor
- * ContentResolver.openAssetFileDescriptor}, or by using the higher-level
+ * inside of their .apk.
+ * This method can be called from multiple threads, as described in
+ * <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
+ * Processes and Threads</a>.
+ *
+ * <p>If you implement this, your clients must be able to deal with such
+ * files, either directly with
+ * {@link ContentResolver#openAssetFileDescriptor}, or by using the higher-level
* {@link ContentResolver#openInputStream ContentResolver.openInputStream}
* or {@link ContentResolver#openOutputStream ContentResolver.openOutputStream}
* methods.
- *
- * <p><em>Note: if you are implementing this to return a full file, you
+ *
+ * <p class="note">If you are implementing this to return a full file, you
* should create the AssetFileDescriptor with
* {@link AssetFileDescriptor#UNKNOWN_LENGTH} to be compatible with
- * applications that can not handle sub-sections of files.</em></p>
+ * applications that can not handle sub-sections of files.</p>
*
* @param uri The URI whose file is to be opened.
* @param mode Access mode for the file. May be "r" for read-only access,
@@ -735,17 +792,20 @@
}
/**
- * Applies each of the {@link ContentProviderOperation} objects and returns an array
- * of their results. Passes through OperationApplicationException, which may be thrown
- * by the call to {@link ContentProviderOperation#apply}.
- * If all the applications succeed then a {@link ContentProviderResult} array with the
- * same number of elements as the operations will be returned. It is implementation-specific
- * how many, if any, operations will have been successfully applied if a call to
- * apply results in a {@link OperationApplicationException}.
+ * Override this to perform a batch of operations, or the default
+ * implementation will {@link ContentProviderOperation#apply} each of the
+ * {@link ContentProviderOperation} objects. If the apply calls all succeed
+ * then a {@link ContentProviderResult} array with the same number of
+ * elements as the operations will be returned. If any of the apply calls
+ * fail, it is up to the implementation how many of the others take effect.
+ * This method can be called from multiple threads, as described in
+ * <a href="{@docRoot}guide/topics/fundamentals.html#procthread">Application Fundamentals:
+ * Processes and Threads</a>.
+ *
* @param operations the operations to apply
* @return the results of the applications
- * @throws OperationApplicationException thrown if an application fails.
- * See {@link ContentProviderOperation#apply} for more information.
+ * @throws OperationApplicationException thrown if any operation fails.
+ * @see ContentProviderOperation#apply
*/
public ContentProviderResult[] applyBatch(ArrayList<ContentProviderOperation> operations)
throws OperationApplicationException {