Most interaction with a message loop is through the * {@link Handler} class. * *
This is a typical example of the implementation of a Looper thread, * using the separation of {@link #prepare} and {@link #loop} to create an * initial Handler to communicate with the Looper. * *
* class LooperThread extends Thread {
* public Handler mHandler;
*
* public void run() {
* Looper.prepare();
*
* mHandler = new Handler() {
* public void handleMessage(Message msg) {
* // process incoming messages here
* }
* };
*
* Looper.loop();
* }
* }
*/
public class Looper {
private static final boolean DEBUG = false;
private static final boolean localLOGV = DEBUG ? Config.LOGD : Config.LOGV;
// sThreadLocal.get() will return null unless you've called prepare().
private static final ThreadLocal sThreadLocal = new ThreadLocal();
final MessageQueue mQueue;
volatile boolean mRun;
Thread mThread;
private Printer mLogging = null;
private static Looper mMainLooper = null;
/** Initialize the current thread as a looper.
* This gives you a chance to create handlers that then reference
* this looper, before actually starting the loop. Be sure to call
* {@link #loop()} after calling this method, and end it by calling
* {@link #quit()}.
*/
public static final void prepare() {
if (sThreadLocal.get() != null) {
throw new RuntimeException("Only one Looper may be created per thread");
}
sThreadLocal.set(new Looper());
}
/** Initialize the current thread as a looper, marking it as an application's main
* looper. The main looper for your application is created by the Android environment,
* so you should never need to call this function yourself.
* {@link #prepare()}
*/
public static final void prepareMainLooper() {
prepare();
setMainLooper(myLooper());
if (Process.supportsProcesses()) {
myLooper().mQueue.mQuitAllowed = false;
}
}
private synchronized static void setMainLooper(Looper looper) {
mMainLooper = looper;
}
/** Returns the application's main looper, which lives in the main thread of the application.
*/
public synchronized static final Looper getMainLooper() {
return mMainLooper;
}
/**
* Run the message queue in this thread. Be sure to call
* {@link #quit()} to end the loop.
*/
public static final void loop() {
Looper me = myLooper();
MessageQueue queue = me.mQueue;
while (true) {
Message msg = queue.next(); // might block
//if (!me.mRun) {
// break;
//}
if (msg != null) {
if (msg.target == null) {
// No target is a magic identifier for the quit message.
return;
}
if (me.mLogging!= null) me.mLogging.println(
">>>>> Dispatching to " + msg.target + " "
+ msg.callback + ": " + msg.what
);
msg.target.dispatchMessage(msg);
if (me.mLogging!= null) me.mLogging.println(
"<<<<< Finished to " + msg.target + " "
+ msg.callback);
msg.recycle();
}
}
}
/**
* Return the Looper object associated with the current thread. Returns
* null if the calling thread is not associated with a Looper.
*/
public static final Looper myLooper() {
return (Looper)sThreadLocal.get();
}
/**
* Control logging of messages as they are processed by this Looper. If
* enabled, a log message will be written to printer
* at the beginning and ending of each message dispatch, identifying the
* target Handler and message contents.
*
* @param printer A Printer object that will receive log messages, or
* null to disable message logging.
*/
public void setMessageLogging(Printer printer) {
mLogging = printer;
}
/**
* Return the {@link MessageQueue} object associated with the current
* thread. This must be called from a thread running a Looper, or a
* NullPointerException will be thrown.
*/
public static final MessageQueue myQueue() {
return myLooper().mQueue;
}
private Looper() {
mQueue = new MessageQueue();
mRun = true;
mThread = Thread.currentThread();
}
public void quit() {
Message msg = Message.obtain();
// NOTE: By enqueueing directly into the message queue, the
// message is left with a null target. This is how we know it is
// a quit message.
mQueue.enqueueMessage(msg, 0);
}
/**
* Return the Thread associated with this Looper.
*/
public Thread getThread() {
return mThread;
}
public void dump(Printer pw, String prefix) {
pw.println(prefix + this);
pw.println(prefix + "mRun=" + mRun);
pw.println(prefix + "mThread=" + mThread);
pw.println(prefix + "mQueue=" + ((mQueue != null) ? mQueue : "(null"));
if (mQueue != null) {
synchronized (mQueue) {
Message msg = mQueue.mMessages;
int n = 0;
while (msg != null) {
pw.println(prefix + " Message " + n + ": " + msg);
n++;
msg = msg.next;
}
pw.println(prefix + "(Total messages: " + n + ")");
}
}
}
public String toString() {
return "Looper{"
+ Integer.toHexString(System.identityHashCode(this))
+ "}";
}
static class HandlerException extends Exception {
HandlerException(Message message, Throwable cause) {
super(createMessage(cause), cause);
}
static String createMessage(Throwable cause) {
String causeMsg = cause.getMessage();
if (causeMsg == null) {
causeMsg = cause.toString();
}
return causeMsg;
}
}
}