Can anyone point me in the right direction here please ?
I have an activity which spawns two threads, a thread for handling messages, using a Looper
public static class MiddleThread extends Handler{
static public Handler handler;
public void run() {
Looper.prepare();
Log.d("MiddleThread", "Looper is prepared !");
handler = new Handler() {
public void handleMessage(Message msg)
{
Bundle bundle = msg.getData();
String exitString = bundle.getString("endmessage");
if(exitString.equals(("ExitOK")))
{
boolean searchFinished = true;
Looper looper = Looper.myLooper();
looper.quit();
} else
{
int fileCount = bundle.getInt("filecount");
String fileName = bundle.getString("filename");
Log.d("MiddleThread", "File Number " + fileCount + " is " + fileName);
}
}
};
Log.d("MiddleThread", "nandler should be initialised");
Looper.loop();
}
... then it spawns the main Worker Thread, which is passed a handler from the UI Thread, and the handler from the above thread.
public class BasicSearch {
public Handler handlerUi, handlerMiddleThread;
public Message messageUi, messageMiddleThread;
public int fileCount = 0;
public BasicSearch(Handler ui, Handler mt) {
handlerUi = ui;
handlerMiddleThread = mt;
}
public void listFiles()
{
File searchPath = Environment.getExternalStorageDirectory();
messageUi = handlerUi.obtainMessage();
messageMiddleThread = handlerMiddleThread.obtainMessage();
walk(searchPath);
Bundle b = new Bundle();
b.putString("endmessage", "ExitOK");
messageMiddleThread.setData(b);
handlerMiddleThread.dispatchMessage(messageMiddleThread);
}
private void walk(File path) {
File[] list = path.listFiles();
for(File f : list)
{
if(f.isDirectory())
{
walk(new File(f.getAbsolutePath()));
} else {
processFile(f);
}
}
}
private void processFile(File f) {
Bundle b = new Bundle();
fileCount++;
b.putString("filename", f.getName());
b.putInt("filecount", fileCount);
messageMiddleThread.setData(b);
Log.d("BasicSearch", "Data is set, to send to MiddleThread");
handlerMiddleThread.dispatchMessage(messageMiddleThread);
Log.d("BasicSearch", "Message sent");
}
}
Whatever happens, when it tries to dispatchMessage, handlerMiddleThread reverts to being null. I even have the following code in my activity, to try and ensure that it isn't null, but it still ends up being null when I get to send the message.
startMiddleThread();
while(true)
{
if(MiddleThread.handler != null)
break;
}
startSearchThread();
This is a test project, as I wanted to be able to get the Handler/Looper concept properly understood before continuing on with my project.
I have successfully managed to use a Handler in my UI Threads before, but my current project has too much processing going on in the UI, and I want to have a secondary thread handling the output from the searchThread, and just receive a message in UI thread when the thread is complete.
So I think I see what you're trying to do and let me suggest a slightly easier way:
To start your background thread and get a handler to it:
HandlerThread bgThread = new HandlerThread();
bgThread.start();
Handler bgHandler = new Handler(bgThread.getLooper());
Then you can send whatever messages you want to your bgHandler. Note that you need to call start on a HandlerThread before creating the bgThread (otherwise getLooper() will return null).
That being said I think I know whats wrong with your code as you posted it. First, MiddleThread extends Handler (which doesn't have a run() method!) not Thread. Second, the run() method on MiddleThread is never called, so Handler is never instantiated. Even if your just mistyped Handler in your code above and you're actually extending Thread, you still need to call start on MiddleThread in order for anything in run() to be executed. Really though, what you're doing is waaay more complicated that it needs to be, and you almost certainly want to just do what I mentioned above.
Related
I am trying to update my UI from the GLThread with a handler. I have read that everything in "handleMessage" will be performed in the UI Thread but I still get this exception:
05-31 09:22:55.653: E/AndroidRuntime(26273): android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
Here is my handler:
public class VideoPlayerCallback implements Handler.Callback {
public static final int PLAY = 0;
public static final int STOP = 1;
public boolean handleMessage(Message msg) {
if(msg.what == VideoPlayerCallback.PLAY) {
ARVideoTemplate videoTemp = (ARVideoTemplate) msg.obj;
String uriPath = "android.resource://" + getPackageName() +"/raw/"+videoTemp.getFileName();
updateVideo(uriPath); // UI Actions
return true;
}
else if(msg.what == VideoPlayerCallback.STOP){
updateVideo(null); // UI Actions
return true;
}
return false;
}
}
Then something like this to put this handler to my GLRenderer:
Handler player = new Handler(new VideoPlayerCallback());
((ARGLSurfaceView) mGLSurfaceView).setVideoView(player);
And the call from GLRenderer:
Message msg = Message.obtain(mVideoPlayer);
msg.obj = video;
msg.what = VideoPlayerCallback.PLAY;
this.mVideoPlayer.dispatchMessage(msg);
What should I change to access the ui thread properly?
Thank you in advance!
I don't know about that callback-subclassing you are doing, but a handler should work fine, just two things to do:
You create the handler on the thread that it should post code to.
You use the handler.post()-method to post he source to the UI thread, like this:
handler.post(new Runnable() {
#Override
public void run() {
drawStuffToScreen();
}
});
I have found my fault. I have to call
this.mVideoPlayer.sendMessage(msg);
instead of dispatchMessage(msg). Then my handler runs on the UI thread.
I have code which calls a new Thread that connects to an IRC server. The thread has loop to listen for response from the IRC server and calls a method 'ProcessData' to action the response.
On my UI I want to be able to 'QUIT' the IRC server in onStop and onPause. The trouble I have is that when I use a Handler to post a message to my IRC thread which sends a QUIT command to the IRC server it tells me that I am performing network operations on the UI thread.
The handler is setup in my IRCManager class (this class extends Thread and is the class I run on a separate thread.
public Handler networkHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
try {
processData((String) msg.obj);
} catch (IOException e) {
Log.e(TAG, "network handler given an object NOT of type String");
}
super.handleMessage(msg);
}
};
I use the handler from the main activity and instantiate it just after starting the network thread
irc.start();
networkHandler = irc.networkHandler;
In the onPause event I send a message to the handler
Message msg = new Message();
msg.obj = IRCManager.QUIT;
networkHandler.sendMessage(msg);
EDIT: Here is the processData method
void processData(String data) throws IOException {
if (data.contains("PING")) {
String pingId = data.substring(6, data.length());
sendMessage(pong + pingId + "\n");
isConnected = true;
Message msg = new Message();
msg.what = 1;
msg.obj = "test";
handler.sendMessage(msg);
} else if (data.contains("Welcome")) {
sendMessage("PRIVMSG " + BOT_NAME + " JOIN " + siteId + "\n");
} else if (data.contains(IRCManager.QUIT)) {
disconnect();
} else if (isClientConnected()) {
Message msg = new Message();
msg.what = 2;
msg.obj = "test";
handler.sendMessage(msg);
}
}
It seems that the handler isn't linking properly to the thread. Can anyone shed any light on how I can do this?
My thread actually spends 99% of it's time in a while loop checking the inputstream from the IRC server. This may also have something to do with it.
You're creating the instance of the Handler, networkHandler, here:
public Handler networkHandler = new Handler() {
It'll be therefore associated with the UI thread.
And, when you say:
I use the handler from the main activity and instantiate it just after starting the network thread
irc.start();
networkHandler = irc.networkHandler;
You're not creating the instance of the Handler there; you're just grabbing a reference to it.
You actually need to create the instance of the Handler in the run() method of your non-UI Thread.
Try to use another constructor with new Handler(new Handler.Callback() ) inside
Which is the better way to use a handler. Any advantages. All examples I have come across seem to give the inline version.
Using implements Handler.Callback in the class and implementing interface method.
or
Using inline code version
private Handler mHandler = new Handler(){ ....};
The common term or these inline class definitions is Anonymous Classes.
You can read more about the discussion on these in Java/Android: anonymous local classes vs named classes
Essentially the main differences are readbility, speed of coding, re-use and scope.
From a resource point of view the anonymous class creation may cause an overhead in the garbage collector as discussed in Avoid Creating Unnecessary Objects. I am not certain on the exact details of anonymous class creation, however, it is logical that implementing the interface on the class is more efficient.
#WilliamTMallard has provided an example of what NOT to do. In his example, a long and syntacticly complex handler should be implementented on the class rather than anonymous handler because it is harder to read and edit when defined inline.
http://developer.android.com/reference/android/os/Handler.html
package : android.os
public class
Handler
extends Object
A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue. Each Handler instance is associated with a single thread and that thread's message queue. When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it -- from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.
There are two main uses for a Handler:
to schedule messages and runnables to be executed as some point
in the future; and
to enqueue an action to be performed on a different thread than
your own.
Exmaple 1
use handler in app splash page.
if (!isFirstIn) {
mHandler.sendEmptyMessageDelayed(GO_HOME, SPLASH_DELAY_MILLIS);
} else {
mHandler.sendEmptyMessageDelayed(GO_GUIDE, SPLASH_DELAY_MILLIS);
}
/**************************************************************************************
*1. Handler
*/
private Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
if(isAuto){
switch (msg.what) {
case GO_HOME:
goHome();
break;
case GO_GUIDE:
goGuide();
break;
}
}
super.handleMessage(msg);
}
};
private void goHome() {
Intent intent = new Intent(SplashActivity.this, MainAct.class);
SplashActivity.this.startActivity(intent);
SplashActivity.this.finish();
}
private void goGuide() {
Intent intent = new Intent(SplashActivity.this, GuideActivity.class);
SplashActivity.this.startActivity(intent);
SplashActivity.this.finish();
}
Example 2
use Handler request network in child thread if the request work may takes time.
new Thread(new Runnable(){
#Override
public void run() {
String versionPath = Parameters.getCheckVersionPath();
String result = RequestHelper.doGet(versionPath, null);
Message msg = new Message();
Bundle data = new Bundle();
data.putString("result",result);
msg.setData(data);
handler1.sendMessage(msg);
}
}).start();
handler1 = new Handler(){
#Override
public void handleMessage(Message msg) {
String result = msg.getData().getString("result");
JSONObject obj;
try {
obj = new JSONObject(result);
Map<String, String> versionInfo = Helper.getSoftwareVersion(obj);
if (versionInfo != null) {
newVersion = versionInfo.get("version");
updateUrl = versionInfo.get("url");
}
} catch (JSONException e) {
Log.w("net work error!", e);
}
}
};
Example 3
use Handler and Timer to update progress bar.
logobar = (ImageView) findViewById(R.id.splash_bar);//progress bar.
logobarClipe = (ClipDrawable) logobar.getBackground();
timer = new Timer();
timer.schedule(new TimerTask() {
public void run() {
updateLogoBarHandler.sendEmptyMessage(0);
}}, 0, rate);
/**************************************************************************************
*2. Handler
*/
//update progress bar.
private Handler updateLogoBarHandler = new Handler() {
public void handleMessage(Message msg) {
if(logobarClipe.getLevel() < 10000){
//1.update image.
logobarClipe.setLevel(logobarClipe.getLevel() + rate*2);
//2.update text.
float percent = logobarClipe.getLevel() /100;
String percentTxtVerbose = String.valueOf(percent);
String percentTxt = percentTxtVerbose.substring(0, percentTxtVerbose.indexOf('.')) + "%";
bartxt.setText(percentTxt);
}else{
timer.cancel();
}
super.handleMessage(msg);
}
};
This really isn't an answer to the above question because I don't know what "the best way" is, and it likely depends on what you're doing. However, I'll explain what I'm doing and why.
I'm writing an app that serves as a remote controller. There are several activities that will interact with the controlled device, and different things need to happen based on the result of the command and the activity it came from. Two things I didn't like about handlers are A) that they end up being a sort of "kitchen sink" construct, implementing functionality from different sources, and B) that they separated an action (the send of the command in my case) from the processing of the result of that action. However, using an anonymous (right term? I'm such a noob.) handler as a parameter allows me to keep the logic together. Here's the pseudocode for my approach:
command = "Wake up!";
mDeviceInterface.write(command, new Handler() {
#Override
public void handleMessage(Message msg) {
switch(msg.what) {
case DeviceInterface.MESSAGE_TIMEOUT: // Process the timeout.
announce("Device not responding.");
break;
case DeviceInterface.MESSAGE_READ: // Process the response.
byte[] readBuf = (byte[]) msg.obj;
if (readBuf[0] == 0x05) {
// Success, update device status.
} else {
announce("Error!");
break;
}
}
}
});
(Always remember, this is probably worth exactly what you've paid for it. ;) )
There is a danger in using anonymous classes in Android. As described in this blog post -
In Java, non-static inner and anonymous classes hold an implicit
reference to their outer class.
And here comes an opportunity for a leak.
So, the short answer would be: implement the interface methods or use static inner classes (which don't hold an outer class reference).
For instance, a leak-safe Handler could look like this:
private static class ChangeTextHandler extends Handler {
private final WeakReference activity;
public ChangeTextHandler(MainActivity activity) {
this.activity = new WeakReference<>(activity);
}
#Override
public void handleMessage(Message msg) {
MainActivity activity = this.activity.get();
if (activity == null) {
Log.e(TAG, "Activity is null ChangeTextHandler.handleMessage()!");
return;
}
final String text = (String) msg.getData().get(BUNDLE_KEY);
if (!TextUtils.isEmpty(text)) {
switch (msg.what) {
// do something
}
}
}
}
I made a blog post around usage of Handlers, so might be worth checking as well :)
This question is about event handling on Android. It is not specific to c++.
I need to process UI/OS events, without blocking when all events have been processed.
The reason is that the application I am porting is very large and can't easily be rewritten to deal with its own stuff on a worker thread. Instead the application engine asks for UI/OS events to be processed during long-winded operations that would otherwise be blocking.
I have found that ALooper_pollAll(...) doesn't do this for me. If I, for example, create a dialog in my activity and start a long operation, ALooper_pollAll() won't make my dialog appear - it will show only when I return to the main loop (I tested this in onNativeWindowCreated).
The only solution that I have found to almost work is to do an inner loop on the UI thread, by calling the following code through JNI:
public class MyActivity extends NativeActivity {
private Handler _uiEventsHandler = null;
private Runnable _uiEventsTask = new Runnable() {
public void run() {
Looper looper = Looper.myLooper();
looper.quit();
_uiEventsHandler.removeCallbacks(this);
_uiEventsHandler = null;
}
};
public void ProcessEvents(int timeout)
{
if (_uiEventsHandler==null) {
Looper looper = Looper.myLooper();
_uiEventsHandler = new Handler(looper);
_uiEventsHandler.removeCallbacks(_uiEventsTask);
//_uiEventsHandler.postDelayed(_uiEventsTask,timeout);
_uiEventsHandler.post(_uiEventsTask);
try {
looper.loop();
} catch (RuntimeException re) {
// We get an exception when we try to quit the loop, but the inner loop actually terminates
}
}
}
}
This is, however, not an optimal solution, because it will not loop until there would be no more events to process (because events may be created during the run of the loop).
During my research I have found that I can get the MessageQueue from the Looper and add an IdleHandler that can quit my inner loop. I haven't tried this yet, there has to be a better way.
Given the fact that this is the architecture I must stick with, what is a better solution?
Update:
Using the MessageQueue I'm able to achieve what I need:
public class MyActivity extends NativeActivity {
private class IdleHandler implements MessageQueue.IdleHandler {
private Looper _looper;
protected IdleHandler(Looper looper) {
_looper = looper;
}
public boolean queueIdle() {
_uiEventsHandler = new Handler(_looper);
_uiEventsHandler.post(_uiEventsTask);
return(false);
}
};
private boolean _processingEventsf = false;
private Handler _uiEventsHandler = null;
private Runnable _uiEventsTask = new Runnable() {
public void run() {
Looper looper = Looper.myLooper();
looper.quit();
_uiEventsHandler.removeCallbacks(this);
_uiEventsHandler = null;
}
};
public void ProcessEvents()
{
if (!_processingEventsf) {
Looper looper = Looper.myLooper();
looper.myQueue().addIdleHandler(new IdleHandler(looper));
_processingEventsf = true;
try {
looper.loop();
} catch (RuntimeException re) {
// We get an exception when we try to quit the loop.
}
_processingEventsf = false;
}
}
}
However, I still would like to know if there is a better solution.
Not sure if I understood the question correctly but have you tried using an IntentService?
http://developer.android.com/reference/android/app/IntentService.html
From the docs:
This "work queue processor" pattern is commonly used to offload tasks from an application's main thread. The IntentService class exists to simplify this pattern and take care of the mechanics."
So, I am getting an error that I am updating the UI from the wrong thread. This of course was not my intention. My case is quite long, but I will try to do it justice with code snippets. My end goal is to run an expensive task in a separate thread and post update that happen along the way and at the end to my listView.
public class test extends Activity {
private ArrayAdapter<String> _mOutArrayAdapter;
private ListView _mOutView;
private EditText _mCmdEditText;
private Button _mRunButton;
private Interpreter _interpreter;
// Need handler for callbacks to the UI thread
public final Handler _mHandler = new Handler() {
public void handleMessage(Message msg) {
_mOutArrayAdapter.add(msg.getData().getString("text"));
};
};
// Create runnable for posting
final Runnable mUpdateResults = new Runnable() {
public void run() {
updateResultsInUi();
}
};
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
_interpreter = new Interpreter(true);
_mOutView = (ListView)findViewById(R.id.out);
_mCmdEditText = (EditText)findViewById(R.id.edit_command);
_mRunButton = (Button)findViewById(R.id.button_run);
_mOutArrayAdapter = new ArrayAdapter<String>(this, R.layout.message);
_mOutView.setAdapter(_mOutArrayAdapter);
_mOutArrayAdapter.clear();
_interpreter.setOutputAdapter(_mOutArrayAdapter);
Thread t = new Thread() {
public void run() {
_mResults = _interpreter.executeExpression("startup;",_mHandler);
_mHandler.post(mUpdateResults);
}
};
t.start();
);
And then inside inpterpreter I do this:
public class Interpreter
{
private static Handler _mHandler;
public String executeExpression(String expression, Handler handler)
{
_mHandler = handler;
//Do a bunch of stuff that sometimes calls displayText from this class or from others
return answer;
}
public void displayText(String text)
{
Message msg = new Message();
Bundle bndl = new Bundle();
bndl.putString("text", text);
msg.setData(bndl);
_mHandler.dispatchMessage(msg);
}
}
The display of the final answer works. And the dispatchMessage is ending up triggering handleMessage, but it throw an error that I cannot modify the UI from outside of the UI thread which I know is illegal. So, what am I doing wrong?
Thanks!
_mHandler.dispatchMessage(msg);
dispatchMessage() causes the Handler to be run on the current thread.
http://developer.android.com/reference/android/os/Handler.html
dispatchMessage(Message msg)
Handle system messages here.
You should be using _mHandler.sendMessage(msg); It will put the message on the queue to be run by the Thread that declared the Handler.
sendMessage(Message msg)
Pushes a message onto the end of the message queue after all pending messages before the current time.
I would strongly suggest you stick with an AsyncTask (or one of the droid-fu versions if you need rotation/background support) unless you know what you're getting into. It'll help you cleanly keep track of what code is running in your UI thread and what code is in the background task, and save you a lot of confusion that dealing with Threads and Handlers yourself can cause.
Handler's post method requires a Runnable object in parameter, and scheduling execution of that runnable block. Instead you can use Handler.sendEmptyMessage() or Handler.sendMessage() to send a message to Handler. SO change your code to following:
Thread t = new Thread() {
public void run() {
_mResults = _interpreter.executeExpression("startup;",_mHandler);
Message msg= _mHandler.obtainMessage();
msg.obj= _mResults;
_mHandler.sendMessage(msg);
}
};