Note on threading: Clients of loaders should as a rule perform * any calls on to a Loader from the main thread of their process (that is, * the thread the Activity callbacks and other things occur on). Subclasses * of Loader (such as {@link AsyncTaskLoader}) will often perform their work * in a separate thread, but when delivering their results this too should * be done on the main thread.
* *Subclasses generally must implement at least {@link #onStartLoading()}, * {@link #onStopLoading()}, {@link #onForceLoad()}, and {@link #onReset()}.
* *Most implementations should not derive directly from this class, but * instead inherit from {@link AsyncTaskLoader}.
* *For more information about using loaders, read the * Loaders developer guide.
*Must be called from the process's main thread.
*/
public void registerListener(int id, OnLoadCompleteListener This updates the Loader's internal state so that
* {@link #isStarted()} and {@link #isReset()} will return the correct
* values, and then calls the implementation's {@link #onStartLoading()}.
*
* Must be called from the process's main thread.
*/
public final void startLoading() {
mStarted = true;
mReset = false;
mAbandoned = false;
onStartLoading();
}
/**
* Subclasses must implement this to take care of loading their data,
* as per {@link #startLoading()}. This is not called by clients directly,
* but as a result of a call to {@link #startLoading()}.
*/
protected void onStartLoading() {
}
/**
* Attempt to cancel the current load task.
* Must be called on the main thread of the process.
*
* Cancellation is not an immediate operation, since the load is performed
* in a background thread. If there is currently a load in progress, this
* method requests that the load be canceled, and notes this is the case;
* once the background thread has completed its work its remaining state
* will be cleared. If another load request comes in during this time,
* it will be held until the canceled load is complete.
*
* @return Returns false if the task could not be canceled,
* typically because it has already completed normally, or
* because {@link #startLoading()} hasn't been called; returns
* true otherwise. When true is returned, the task
* is still running and the {@link OnLoadCanceledListener} will be called
* when the task completes.
*/
public boolean cancelLoad() {
return onCancelLoad();
}
/**
* Subclasses must implement this to take care of requests to {@link #cancelLoad()}.
* This will always be called from the process's main thread.
*
* @return Returns false if the task could not be canceled,
* typically because it has already completed normally, or
* because {@link #startLoading()} hasn't been called; returns
* true otherwise. When true is returned, the task
* is still running and the {@link OnLoadCanceledListener} will be called
* when the task completes.
*/
protected boolean onCancelLoad() {
return false;
}
/**
* Force an asynchronous load. Unlike {@link #startLoading()} this will ignore a previously
* loaded data set and load a new one. This simply calls through to the
* implementation's {@link #onForceLoad()}. You generally should only call this
* when the loader is started -- that is, {@link #isStarted()} returns true.
*
* Must be called from the process's main thread.
*/
public void forceLoad() {
onForceLoad();
}
/**
* Subclasses must implement this to take care of requests to {@link #forceLoad()}.
* This will always be called from the process's main thread.
*/
protected void onForceLoad() {
}
/**
* This function will normally be called for you automatically by
* {@link android.app.LoaderManager} when the associated fragment/activity
* is being stopped. When using a Loader with {@link android.app.LoaderManager},
* you must not call this method yourself, or you will conflict
* with its management of the Loader.
*
* Stops delivery of updates until the next time {@link #startLoading()} is called.
* Implementations should not invalidate their data at this point --
* clients are still free to use the last data the loader reported. They will,
* however, typically stop reporting new data if the data changes; they can
* still monitor for changes, but must not report them to the client until and
* if {@link #startLoading()} is later called.
*
* This updates the Loader's internal state so that
* {@link #isStarted()} will return the correct
* value, and then calls the implementation's {@link #onStopLoading()}.
*
* Must be called from the process's main thread.
*/
public void stopLoading() {
mStarted = false;
onStopLoading();
}
/**
* Subclasses must implement this to take care of stopping their loader,
* as per {@link #stopLoading()}. This is not called by clients directly,
* but as a result of a call to {@link #stopLoading()}.
* This will always be called from the process's main thread.
*/
protected void onStopLoading() {
}
/**
* This function will normally be called for you automatically by
* {@link android.app.LoaderManager} when restarting a Loader. When using
* a Loader with {@link android.app.LoaderManager},
* you must not call this method yourself, or you will conflict
* with its management of the Loader.
*
* Tell the Loader that it is being abandoned. This is called prior
* to {@link #reset} to have it retain its current data but not report
* any new data.
*/
public void abandon() {
mAbandoned = true;
onAbandon();
}
/**
* Subclasses implement this to take care of being abandoned. This is
* an optional intermediate state prior to {@link #onReset()} -- it means that
* the client is no longer interested in any new data from the loader,
* so the loader must not report any further updates. However, the
* loader must keep its last reported data valid until the final
* {@link #onReset()} happens. You can retrieve the current abandoned
* state with {@link #isAbandoned}.
*/
protected void onAbandon() {
}
/**
* This function will normally be called for you automatically by
* {@link android.app.LoaderManager} when destroying a Loader. When using
* a Loader with {@link android.app.LoaderManager},
* you must not call this method yourself, or you will conflict
* with its management of the Loader.
*
* Resets the state of the Loader. The Loader should at this point free
* all of its resources, since it may never be called again; however, its
* {@link #startLoading()} may later be called at which point it must be
* able to start running again.
*
* This updates the Loader's internal state so that
* {@link #isStarted()} and {@link #isReset()} will return the correct
* values, and then calls the implementation's {@link #onReset()}.
*
* Must be called from the process's main thread.
*/
public void reset() {
onReset();
mReset = true;
mStarted = false;
mAbandoned = false;
mContentChanged = false;
mProcessingChange = false;
}
/**
* Subclasses must implement this to take care of resetting their loader,
* as per {@link #reset()}. This is not called by clients directly,
* but as a result of a call to {@link #reset()}.
* This will always be called from the process's main thread.
*/
protected void onReset() {
}
/**
* Take the current flag indicating whether the loader's content had
* changed while it was stopped. If it had, true is returned and the
* flag is cleared.
*/
public boolean takeContentChanged() {
boolean res = mContentChanged;
mContentChanged = false;
mProcessingChange |= res;
return res;
}
/**
* Commit that you have actually fully processed a content change that
* was returned by {@link #takeContentChanged}. This is for use with
* {@link #rollbackContentChanged()} to handle situations where a load
* is cancelled. Call this when you have completely processed a load
* without it being cancelled.
*/
public void commitContentChanged() {
mProcessingChange = false;
}
/**
* Report that you have abandoned the processing of a content change that
* was returned by {@link #takeContentChanged()} and would like to rollback
* to the state where there is again a pending content change. This is
* to handle the case where a data load due to a content change has been
* canceled before its data was delivered back to the loader.
*/
public void rollbackContentChanged() {
if (mProcessingChange) {
mContentChanged = true;
}
}
/**
* Called when {@link ForceLoadContentObserver} detects a change. The
* default implementation checks to see if the loader is currently started;
* if so, it simply calls {@link #forceLoad()}; otherwise, it sets a flag
* so that {@link #takeContentChanged()} returns true.
*
* Must be called from the process's main thread.
*/
public void onContentChanged() {
if (mStarted) {
forceLoad();
} else {
// This loader has been stopped, so we don't want to load
// new data right now... but keep track of it changing to
// refresh later if we start again.
mContentChanged = true;
}
}
/**
* For debugging, converts an instance of the Loader's data class to
* a string that can be printed. Must handle a null data.
*/
public String dataToString(D data) {
StringBuilder sb = new StringBuilder(64);
DebugUtils.buildShortClassTag(data, sb);
sb.append("}");
return sb.toString();
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder(64);
DebugUtils.buildShortClassTag(this, sb);
sb.append(" id=");
sb.append(mId);
sb.append("}");
return sb.toString();
}
/**
* Print the Loader's state into the given stream.
*
* @param prefix Text to print at the front of each line.
* @param fd The raw file descriptor that the dump is being sent to.
* @param writer A PrintWriter to which the dump is to be set.
* @param args Additional arguments to the dump request.
*/
public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
writer.print(prefix); writer.print("mId="); writer.print(mId);
writer.print(" mListener="); writer.println(mListener);
if (mStarted || mContentChanged || mProcessingChange) {
writer.print(prefix); writer.print("mStarted="); writer.print(mStarted);
writer.print(" mContentChanged="); writer.print(mContentChanged);
writer.print(" mProcessingChange="); writer.println(mProcessingChange);
}
if (mAbandoned || mReset) {
writer.print(prefix); writer.print("mAbandoned="); writer.print(mAbandoned);
writer.print(" mReset="); writer.println(mReset);
}
}
}