Related
What does the following exception mean; how can I fix it?
This is the code:
Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);
This is the exception:
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:121)
at android.widget.Toast.<init>(Toast.java:68)
at android.widget.Toast.makeText(Toast.java:231)
You need to call Toast.makeText(...) from the UI thread:
activity.runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();
}
});
This is copy-pasted from another (duplicate) SO answer.
You're calling it from a worker thread. You need to call Toast.makeText() (and most other functions dealing with the UI) from within the main thread. You could use a handler, for example.
Look up Communicating with the UI Thread in the documentation. In a nutshell:
// Set this up in the UI thread.
mHandler = new Handler(Looper.getMainLooper()) {
#Override
public void handleMessage(Message message) {
// This is where you do your work in the UI thread.
// Your worker tells you in the message what to do.
}
};
void workerThread() {
// And this is how you call it from the worker thread:
Message message = mHandler.obtainMessage(command, parameter);
message.sendToTarget();
}
Other options:
You could use Activity.runOnUiThread(). Straightforward if you have an Activity:
#WorkerThread
void workerThread() {
myActivity.runOnUiThread(() -> {
// This is where your UI code goes.
}
}
You could also post to the main looper. This works great if all you have is a Context.
#WorkerThread
void workerThread() {
ContextCompat.getMainExecutor(context).execute(() -> {
// This is where your UI code goes.
}
}
Deprecated:
You could use an AsyncTask, that works well for most things running in the background. It has hooks that you can call to indicate the progress, and when it's done.
It's convenient, but can leak contexts if not used correctly. It's been officially deprecated, and you shouldn't use it anymore.
UPDATE - 2016
The best alternative is to use RxAndroid (specific bindings for RxJava) for the P in MVP to take charge fo data.
Start by returning Observable from your existing method.
private Observable<PojoObject> getObservableItems() {
return Observable.create(subscriber -> {
for (PojoObject pojoObject: pojoObjects) {
subscriber.onNext(pojoObject);
}
subscriber.onCompleted();
});
}
Use this Observable like this -
getObservableItems().
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread()).
subscribe(new Observer<PojoObject> () {
#Override
public void onCompleted() {
// Print Toast on completion
}
#Override
public void onError(Throwable e) {}
#Override
public void onNext(PojoObject pojoObject) {
// Show Progress
}
});
}
----------------------------------------------------------------------------------------------------------------------------------
I know I am a little late but here goes.
Android basically works on two thread types namely UI thread and background thread. According to android documentation -
Do not access the Android UI toolkit from outside the UI thread to fix this problem, Android offers several ways to access the UI thread from other threads. Here is a list of methods that can help:
Activity.runOnUiThread(Runnable)
View.post(Runnable)
View.postDelayed(Runnable, long)
Now there are various methods to solve this problem.
I will explain it by code sample:
runOnUiThread
new Thread()
{
public void run()
{
myactivity.this.runOnUiThread(new Runnable()
{
public void run()
{
//Do your UI operations like dialog opening or Toast here
}
});
}
}.start();
LOOPER
Class used to run a message loop for a thread. Threads by default do
not have a message loop associated with them; to create one, call
prepare() in the thread that is to run the loop, and then loop() to
have it process messages until the loop is stopped.
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();
}
}
AsyncTask
AsyncTask allows you to perform asynchronous work on your user
interface. It performs the blocking operations in a worker thread and
then publishes the results on the UI thread, without requiring you to
handle threads and/or handlers yourself.
public void onClick(View v) {
new CustomTask().execute((Void[])null);
}
private class CustomTask extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... param) {
//Do some work
return null;
}
protected void onPostExecute(Void param) {
//Print Toast or open dialog
}
}
Handler
A Handler allows you to send and process Message and Runnable objects
associated with a thread's MessageQueue.
Message msg = new Message();
new Thread()
{
public void run()
{
msg.arg1=1;
handler.sendMessage(msg);
}
}.start();
Handler handler = new Handler(new Handler.Callback() {
#Override
public boolean handleMessage(Message msg) {
if(msg.arg1==1)
{
//Print Toast or open dialog
}
return false;
}
});
Toast.makeText() can only be called from Main/UI thread. Looper.getMainLooper() helps you to achieve it:
JAVA
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
// write your code here
}
});
KOTLIN
Handler(Looper.getMainLooper()).post {
// write your code here
}
An advantage of this method is that you can run UI code without Activity or Context.
Try this, when you see runtimeException due to Looper not prepared before handler.
Handler handler = new Handler(Looper.getMainLooper());
handler.postDelayed(new Runnable() {
#Override
public void run() {
// Run your task here
}
}, 1000 );
I ran into the same problem, and here is how I fixed it:
private final class UIHandler extends Handler
{
public static final int DISPLAY_UI_TOAST = 0;
public static final int DISPLAY_UI_DIALOG = 1;
public UIHandler(Looper looper)
{
super(looper);
}
#Override
public void handleMessage(Message msg)
{
switch(msg.what)
{
case UIHandler.DISPLAY_UI_TOAST:
{
Context context = getApplicationContext();
Toast t = Toast.makeText(context, (String)msg.obj, Toast.LENGTH_LONG);
t.show();
}
case UIHandler.DISPLAY_UI_DIALOG:
//TBD
default:
break;
}
}
}
protected void handleUIRequest(String message)
{
Message msg = uiHandler.obtainMessage(UIHandler.DISPLAY_UI_TOAST);
msg.obj = message;
uiHandler.sendMessage(msg);
}
To create the UIHandler, you'll need to perform the following:
HandlerThread uiThread = new HandlerThread("UIHandler");
uiThread.start();
uiHandler = new UIHandler((HandlerThread) uiThread.getLooper());
Hope this helps.
Reason for an error:
Worker threads are meant for doing background tasks and you can't show anything on UI within a worker thread unless you call method like runOnUiThread. If you try to show anything on UI thread without calling runOnUiThread, there will be a java.lang.RuntimeException.
So, if you are in an activity but calling Toast.makeText() from worker thread, do this:
runOnUiThread(new Runnable()
{
public void run()
{
Toast toast = Toast.makeText(getApplicationContext(), "Something", Toast.LENGTH_SHORT).show();
}
});
The above code ensures that you are showing the Toast message in a UI thread since you are calling it inside runOnUiThread method. So no more java.lang.RuntimeException.
that's what i did.
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
Toast(...);
}
});
Visual components are "locked" to changes from outside threads.
So, since the toast shows stuff on the main screen that is managed by the main thread, you need to run this code on that thread.
Hope that helps:)
I was getting this error until I did the following.
public void somethingHappened(final Context context)
{
Handler handler = new Handler(Looper.getMainLooper());
handler.post(
new Runnable()
{
#Override
public void run()
{
Toast.makeText(context, "Something happened.", Toast.LENGTH_SHORT).show();
}
}
);
}
And made this into a singleton class:
public enum Toaster {
INSTANCE;
private final Handler handler = new Handler(Looper.getMainLooper());
public void postMessage(final String message) {
handler.post(
new Runnable() {
#Override
public void run() {
Toast.makeText(ApplicationHolder.INSTANCE.getCustomApplication(), message, Toast.LENGTH_SHORT)
.show();
}
}
);
}
}
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(mContext, "Message", Toast.LENGTH_SHORT).show();
}
});
Wonderful Kotlin solution:
runOnUiThread {
// Add your ui thread code here
}
first call Looper.prepare() and then call Toast.makeText().show() last call Looper.loop() like:
Looper.prepare() // to be able to make toast
Toast.makeText(context, "not connected", Toast.LENGTH_LONG).show()
Looper.loop()
This is because Toast.makeText() is calling from a worker thread. It should be call from main UI thread like this
runOnUiThread(new Runnable() {
public void run() {
Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);
}
});
The answer by ChicoBird worked for me. The only change I made was in the creation of the UIHandler where I had to do
HandlerThread uiThread = new HandlerThread("UIHandler");
Eclipse refused to accept anything else. Makes sense I suppose.
Also the uiHandler is clearly a class global defined somewhere. I still don't claim to understand how Android is doing this and what is going on but I am glad it works. Now I will proceed to study it and see if I can understand what Android is doing and why one has to go through all these hoops and loops. Thanks for the help ChicoBird.
For Rxjava and RxAndroid User:
public static void shortToast(String msg) {
Observable.just(msg)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(message -> {
Toast.makeText(App.getInstance(), message, Toast.LENGTH_SHORT).show();
});
}
Coroutine will do it perfectly
CoroutineScope(Job() + Dispatchers.Main).launch {
Toast.makeText(context, "yourmessage",Toast.LENGTH_LONG).show()}
I was running into the same issue when my callbacks would try to show a dialog.
I solved it with dedicated methods in the Activity - at the Activity instance member level - that use runOnUiThread(..)
public void showAuthProgressDialog() {
runOnUiThread(new Runnable() {
#Override
public void run() {
mAuthProgressDialog = DialogUtil.getVisibleProgressDialog(SignInActivity.this, "Loading ...");
}
});
}
public void dismissAuthProgressDialog() {
runOnUiThread(new Runnable() {
#Override
public void run() {
if (mAuthProgressDialog == null || ! mAuthProgressDialog.isShowing()) {
return;
}
mAuthProgressDialog.dismiss();
}
});
}
Java 8
new Handler(Looper.getMainLooper()).post(() -> {
// Work in the UI thread
});
Kotlin
Handler(Looper.getMainLooper()).post{
// Work in the UI thread
}
GL
Handler handler2;
HandlerThread handlerThread=new HandlerThread("second_thread");
handlerThread.start();
handler2=new Handler(handlerThread.getLooper());
Now handler2 will use a different Thread to handle the messages than the main Thread.
To display a dialog or a toaster in a thread, the most concise way is to use the Activity object.
For example:
new Thread(new Runnable() {
#Override
public void run() {
myActivity.runOnUiThread(new Runnable() {
public void run() {
myActivity.this.processingWaitDialog = new ProgressDialog(myActivity.this.getContext());
myActivity.this.processingWaitDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
myActivity.this.processingWaitDialog.setMessage("abc");
myActivity.this.processingWaitDialog.setIndeterminate(true);
myActivity.this.processingWaitDialog.show();
}
});
expenseClassify.serverPost(
new AsyncOperationCallback() {
public void operationCompleted(Object sender) {
myActivity.runOnUiThread(new Runnable() {
public void run() {
if (myActivity.this.processingWaitDialog != null
&& myActivity.this.processingWaitDialog.isShowing()) {
myActivity.this.processingWaitDialog.dismiss();
myActivity.this.processingWaitDialog = null;
}
}
}); // .runOnUiThread(new Runnable()
...
Using lambda:
activity.runOnUiThread(() -> Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show());
Toast, AlertDialogs needs to run on UI thread, you can use Asynctask to use them properly in android development.but some cases we need to customize the time outs, so we use Threads, but in threads we cannot use Toast,Alertdialogs like we using in AsyncTask.So we need separate Handler for popup those.
public void onSigned() {
Thread thread = new Thread(){
#Override
public void run() {
try{
sleep(3000);
Message message = new Message();
message.what = 2;
handler.sendMessage(message);
} catch (Exception e){
e.printStackTrace();
}
}
};
thread.start();
}
in Above example i want to sleep my thread in 3sec and after i want to show a Toast message,for that in your mainthread implement handler.
handler = new Handler() {
public void handleMessage(Message msg) {
switch(msg.what){
case 1:
Toast.makeText(getActivity(),"cool",Toast.LENGTH_SHORT).show();
break;
}
super.handleMessage(msg);
}
};
I used switch case here, because if you need to show different message in same way, you can use switch case within Handler class...hope this will help you
This usually happens when something on the main thread is called from any background thread. Lets look at an example , for instance.
private class MyTask extends AsyncTask<Void, Void, Void> {
#Override
protected Void doInBackground(Void... voids) {
textView.setText("Any Text");
return null;
}
}
In the above example , we are setting text on the textview which is in the main UI thread from doInBackground() method , which operates only on a worker thread.
I had the same problem and I fixed it simply by putting the Toast in onPostExecute() override function of the Asynctask<> and it worked.
You need to create toast on UI thread. Find the example below.
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(activity, "YOUR_MESSAGE", Toast.LENGTH_SHORT).show();
}
});
For displaying Toast message please refer to this article
Here is the solution for Kotlin using Coroutine:
Extend your class with CoroutineScope by MainScope():
class BootstrapActivity : CoroutineScope by MainScope() {}
Then simply do this:
launch {
// whatever you want to do in the main thread
}
Don't forget to add the dependencies for coroutine:
org.jetbrains.kotlinx:kotlinx-coroutines-core:${Versions.kotlinCoroutines}
org.jetbrains.kotlinx:kotlinx-coroutines-android:${Versions.kotlinCoroutines}
Create Handler outside the Thread
final Handler handler = new Handler();
new Thread(new Runnable() {
#Override
public void run() {
try{
handler.post(new Runnable() {
#Override
public void run() {
showAlertDialog(p.getProviderName(), Token, p.getProviderId(), Amount);
}
});
}
}
catch (Exception e){
Log.d("ProvidersNullExp", e.getMessage());
}
}
}).start();
Recently, I encounter this problem - It was happening because I was trying to call a function that was to do some UI stuff from the constructor. Removing the initialization from the constructor solved the problem for me.
I got the same problem and this code is working fine for me now.
As an example this is my code to do a task in the background and UI thread.
Observe how the looper is used:
new Thread(new Runnable() {
#Override
public void run() {
Looper.prepare();
// your Background Task here
runOnUiThread(new Runnable() {
#Override
public void run() {
// update your UI here
Looper.loop();
}
});
}
}).start();
i use the following code to show message from non main thread "context",
#FunctionalInterface
public interface IShowMessage {
Context getContext();
default void showMessage(String message) {
final Thread mThread = new Thread() {
#Override
public void run() {
try {
Looper.prepare();
Toast.makeText(getContext(), message, Toast.LENGTH_LONG).show();
Looper.loop();
} catch (Exception error) {
error.printStackTrace();
Log.e("IShowMessage", error.getMessage());
}
}
};
mThread.start();
}
}
then use as the following:
class myClass implements IShowMessage{
showMessage("your message!");
#Override
public Context getContext() {
return getApplicationContext();
}
}
What does the following exception mean; how can I fix it?
This is the code:
Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);
This is the exception:
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
at android.os.Handler.<init>(Handler.java:121)
at android.widget.Toast.<init>(Toast.java:68)
at android.widget.Toast.makeText(Toast.java:231)
You need to call Toast.makeText(...) from the UI thread:
activity.runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();
}
});
This is copy-pasted from another (duplicate) SO answer.
You're calling it from a worker thread. You need to call Toast.makeText() (and most other functions dealing with the UI) from within the main thread. You could use a handler, for example.
Look up Communicating with the UI Thread in the documentation. In a nutshell:
// Set this up in the UI thread.
mHandler = new Handler(Looper.getMainLooper()) {
#Override
public void handleMessage(Message message) {
// This is where you do your work in the UI thread.
// Your worker tells you in the message what to do.
}
};
void workerThread() {
// And this is how you call it from the worker thread:
Message message = mHandler.obtainMessage(command, parameter);
message.sendToTarget();
}
Other options:
You could use Activity.runOnUiThread(). Straightforward if you have an Activity:
#WorkerThread
void workerThread() {
myActivity.runOnUiThread(() -> {
// This is where your UI code goes.
}
}
You could also post to the main looper. This works great if all you have is a Context.
#WorkerThread
void workerThread() {
ContextCompat.getMainExecutor(context).execute(() -> {
// This is where your UI code goes.
}
}
Deprecated:
You could use an AsyncTask, that works well for most things running in the background. It has hooks that you can call to indicate the progress, and when it's done.
It's convenient, but can leak contexts if not used correctly. It's been officially deprecated, and you shouldn't use it anymore.
UPDATE - 2016
The best alternative is to use RxAndroid (specific bindings for RxJava) for the P in MVP to take charge fo data.
Start by returning Observable from your existing method.
private Observable<PojoObject> getObservableItems() {
return Observable.create(subscriber -> {
for (PojoObject pojoObject: pojoObjects) {
subscriber.onNext(pojoObject);
}
subscriber.onCompleted();
});
}
Use this Observable like this -
getObservableItems().
subscribeOn(Schedulers.io()).
observeOn(AndroidSchedulers.mainThread()).
subscribe(new Observer<PojoObject> () {
#Override
public void onCompleted() {
// Print Toast on completion
}
#Override
public void onError(Throwable e) {}
#Override
public void onNext(PojoObject pojoObject) {
// Show Progress
}
});
}
----------------------------------------------------------------------------------------------------------------------------------
I know I am a little late but here goes.
Android basically works on two thread types namely UI thread and background thread. According to android documentation -
Do not access the Android UI toolkit from outside the UI thread to fix this problem, Android offers several ways to access the UI thread from other threads. Here is a list of methods that can help:
Activity.runOnUiThread(Runnable)
View.post(Runnable)
View.postDelayed(Runnable, long)
Now there are various methods to solve this problem.
I will explain it by code sample:
runOnUiThread
new Thread()
{
public void run()
{
myactivity.this.runOnUiThread(new Runnable()
{
public void run()
{
//Do your UI operations like dialog opening or Toast here
}
});
}
}.start();
LOOPER
Class used to run a message loop for a thread. Threads by default do
not have a message loop associated with them; to create one, call
prepare() in the thread that is to run the loop, and then loop() to
have it process messages until the loop is stopped.
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();
}
}
AsyncTask
AsyncTask allows you to perform asynchronous work on your user
interface. It performs the blocking operations in a worker thread and
then publishes the results on the UI thread, without requiring you to
handle threads and/or handlers yourself.
public void onClick(View v) {
new CustomTask().execute((Void[])null);
}
private class CustomTask extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... param) {
//Do some work
return null;
}
protected void onPostExecute(Void param) {
//Print Toast or open dialog
}
}
Handler
A Handler allows you to send and process Message and Runnable objects
associated with a thread's MessageQueue.
Message msg = new Message();
new Thread()
{
public void run()
{
msg.arg1=1;
handler.sendMessage(msg);
}
}.start();
Handler handler = new Handler(new Handler.Callback() {
#Override
public boolean handleMessage(Message msg) {
if(msg.arg1==1)
{
//Print Toast or open dialog
}
return false;
}
});
Toast.makeText() can only be called from Main/UI thread. Looper.getMainLooper() helps you to achieve it:
JAVA
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
// write your code here
}
});
KOTLIN
Handler(Looper.getMainLooper()).post {
// write your code here
}
An advantage of this method is that you can run UI code without Activity or Context.
Try this, when you see runtimeException due to Looper not prepared before handler.
Handler handler = new Handler(Looper.getMainLooper());
handler.postDelayed(new Runnable() {
#Override
public void run() {
// Run your task here
}
}, 1000 );
I ran into the same problem, and here is how I fixed it:
private final class UIHandler extends Handler
{
public static final int DISPLAY_UI_TOAST = 0;
public static final int DISPLAY_UI_DIALOG = 1;
public UIHandler(Looper looper)
{
super(looper);
}
#Override
public void handleMessage(Message msg)
{
switch(msg.what)
{
case UIHandler.DISPLAY_UI_TOAST:
{
Context context = getApplicationContext();
Toast t = Toast.makeText(context, (String)msg.obj, Toast.LENGTH_LONG);
t.show();
}
case UIHandler.DISPLAY_UI_DIALOG:
//TBD
default:
break;
}
}
}
protected void handleUIRequest(String message)
{
Message msg = uiHandler.obtainMessage(UIHandler.DISPLAY_UI_TOAST);
msg.obj = message;
uiHandler.sendMessage(msg);
}
To create the UIHandler, you'll need to perform the following:
HandlerThread uiThread = new HandlerThread("UIHandler");
uiThread.start();
uiHandler = new UIHandler((HandlerThread) uiThread.getLooper());
Hope this helps.
Reason for an error:
Worker threads are meant for doing background tasks and you can't show anything on UI within a worker thread unless you call method like runOnUiThread. If you try to show anything on UI thread without calling runOnUiThread, there will be a java.lang.RuntimeException.
So, if you are in an activity but calling Toast.makeText() from worker thread, do this:
runOnUiThread(new Runnable()
{
public void run()
{
Toast toast = Toast.makeText(getApplicationContext(), "Something", Toast.LENGTH_SHORT).show();
}
});
The above code ensures that you are showing the Toast message in a UI thread since you are calling it inside runOnUiThread method. So no more java.lang.RuntimeException.
that's what i did.
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
Toast(...);
}
});
Visual components are "locked" to changes from outside threads.
So, since the toast shows stuff on the main screen that is managed by the main thread, you need to run this code on that thread.
Hope that helps:)
I was getting this error until I did the following.
public void somethingHappened(final Context context)
{
Handler handler = new Handler(Looper.getMainLooper());
handler.post(
new Runnable()
{
#Override
public void run()
{
Toast.makeText(context, "Something happened.", Toast.LENGTH_SHORT).show();
}
}
);
}
And made this into a singleton class:
public enum Toaster {
INSTANCE;
private final Handler handler = new Handler(Looper.getMainLooper());
public void postMessage(final String message) {
handler.post(
new Runnable() {
#Override
public void run() {
Toast.makeText(ApplicationHolder.INSTANCE.getCustomApplication(), message, Toast.LENGTH_SHORT)
.show();
}
}
);
}
}
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(mContext, "Message", Toast.LENGTH_SHORT).show();
}
});
Wonderful Kotlin solution:
runOnUiThread {
// Add your ui thread code here
}
first call Looper.prepare() and then call Toast.makeText().show() last call Looper.loop() like:
Looper.prepare() // to be able to make toast
Toast.makeText(context, "not connected", Toast.LENGTH_LONG).show()
Looper.loop()
This is because Toast.makeText() is calling from a worker thread. It should be call from main UI thread like this
runOnUiThread(new Runnable() {
public void run() {
Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);
}
});
The answer by ChicoBird worked for me. The only change I made was in the creation of the UIHandler where I had to do
HandlerThread uiThread = new HandlerThread("UIHandler");
Eclipse refused to accept anything else. Makes sense I suppose.
Also the uiHandler is clearly a class global defined somewhere. I still don't claim to understand how Android is doing this and what is going on but I am glad it works. Now I will proceed to study it and see if I can understand what Android is doing and why one has to go through all these hoops and loops. Thanks for the help ChicoBird.
For Rxjava and RxAndroid User:
public static void shortToast(String msg) {
Observable.just(msg)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(message -> {
Toast.makeText(App.getInstance(), message, Toast.LENGTH_SHORT).show();
});
}
Coroutine will do it perfectly
CoroutineScope(Job() + Dispatchers.Main).launch {
Toast.makeText(context, "yourmessage",Toast.LENGTH_LONG).show()}
I was running into the same issue when my callbacks would try to show a dialog.
I solved it with dedicated methods in the Activity - at the Activity instance member level - that use runOnUiThread(..)
public void showAuthProgressDialog() {
runOnUiThread(new Runnable() {
#Override
public void run() {
mAuthProgressDialog = DialogUtil.getVisibleProgressDialog(SignInActivity.this, "Loading ...");
}
});
}
public void dismissAuthProgressDialog() {
runOnUiThread(new Runnable() {
#Override
public void run() {
if (mAuthProgressDialog == null || ! mAuthProgressDialog.isShowing()) {
return;
}
mAuthProgressDialog.dismiss();
}
});
}
Java 8
new Handler(Looper.getMainLooper()).post(() -> {
// Work in the UI thread
});
Kotlin
Handler(Looper.getMainLooper()).post{
// Work in the UI thread
}
GL
Handler handler2;
HandlerThread handlerThread=new HandlerThread("second_thread");
handlerThread.start();
handler2=new Handler(handlerThread.getLooper());
Now handler2 will use a different Thread to handle the messages than the main Thread.
To display a dialog or a toaster in a thread, the most concise way is to use the Activity object.
For example:
new Thread(new Runnable() {
#Override
public void run() {
myActivity.runOnUiThread(new Runnable() {
public void run() {
myActivity.this.processingWaitDialog = new ProgressDialog(myActivity.this.getContext());
myActivity.this.processingWaitDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
myActivity.this.processingWaitDialog.setMessage("abc");
myActivity.this.processingWaitDialog.setIndeterminate(true);
myActivity.this.processingWaitDialog.show();
}
});
expenseClassify.serverPost(
new AsyncOperationCallback() {
public void operationCompleted(Object sender) {
myActivity.runOnUiThread(new Runnable() {
public void run() {
if (myActivity.this.processingWaitDialog != null
&& myActivity.this.processingWaitDialog.isShowing()) {
myActivity.this.processingWaitDialog.dismiss();
myActivity.this.processingWaitDialog = null;
}
}
}); // .runOnUiThread(new Runnable()
...
Using lambda:
activity.runOnUiThread(() -> Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show());
Toast, AlertDialogs needs to run on UI thread, you can use Asynctask to use them properly in android development.but some cases we need to customize the time outs, so we use Threads, but in threads we cannot use Toast,Alertdialogs like we using in AsyncTask.So we need separate Handler for popup those.
public void onSigned() {
Thread thread = new Thread(){
#Override
public void run() {
try{
sleep(3000);
Message message = new Message();
message.what = 2;
handler.sendMessage(message);
} catch (Exception e){
e.printStackTrace();
}
}
};
thread.start();
}
in Above example i want to sleep my thread in 3sec and after i want to show a Toast message,for that in your mainthread implement handler.
handler = new Handler() {
public void handleMessage(Message msg) {
switch(msg.what){
case 1:
Toast.makeText(getActivity(),"cool",Toast.LENGTH_SHORT).show();
break;
}
super.handleMessage(msg);
}
};
I used switch case here, because if you need to show different message in same way, you can use switch case within Handler class...hope this will help you
This usually happens when something on the main thread is called from any background thread. Lets look at an example , for instance.
private class MyTask extends AsyncTask<Void, Void, Void> {
#Override
protected Void doInBackground(Void... voids) {
textView.setText("Any Text");
return null;
}
}
In the above example , we are setting text on the textview which is in the main UI thread from doInBackground() method , which operates only on a worker thread.
I had the same problem and I fixed it simply by putting the Toast in onPostExecute() override function of the Asynctask<> and it worked.
You need to create toast on UI thread. Find the example below.
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(activity, "YOUR_MESSAGE", Toast.LENGTH_SHORT).show();
}
});
For displaying Toast message please refer to this article
Here is the solution for Kotlin using Coroutine:
Extend your class with CoroutineScope by MainScope():
class BootstrapActivity : CoroutineScope by MainScope() {}
Then simply do this:
launch {
// whatever you want to do in the main thread
}
Don't forget to add the dependencies for coroutine:
org.jetbrains.kotlinx:kotlinx-coroutines-core:${Versions.kotlinCoroutines}
org.jetbrains.kotlinx:kotlinx-coroutines-android:${Versions.kotlinCoroutines}
Create Handler outside the Thread
final Handler handler = new Handler();
new Thread(new Runnable() {
#Override
public void run() {
try{
handler.post(new Runnable() {
#Override
public void run() {
showAlertDialog(p.getProviderName(), Token, p.getProviderId(), Amount);
}
});
}
}
catch (Exception e){
Log.d("ProvidersNullExp", e.getMessage());
}
}
}).start();
Recently, I encounter this problem - It was happening because I was trying to call a function that was to do some UI stuff from the constructor. Removing the initialization from the constructor solved the problem for me.
I got the same problem and this code is working fine for me now.
As an example this is my code to do a task in the background and UI thread.
Observe how the looper is used:
new Thread(new Runnable() {
#Override
public void run() {
Looper.prepare();
// your Background Task here
runOnUiThread(new Runnable() {
#Override
public void run() {
// update your UI here
Looper.loop();
}
});
}
}).start();
i use the following code to show message from non main thread "context",
#FunctionalInterface
public interface IShowMessage {
Context getContext();
default void showMessage(String message) {
final Thread mThread = new Thread() {
#Override
public void run() {
try {
Looper.prepare();
Toast.makeText(getContext(), message, Toast.LENGTH_LONG).show();
Looper.loop();
} catch (Exception error) {
error.printStackTrace();
Log.e("IShowMessage", error.getMessage());
}
}
};
mThread.start();
}
}
then use as the following:
class myClass implements IShowMessage{
showMessage("your message!");
#Override
public Context getContext() {
return getApplicationContext();
}
}
I'm trying to understand how Handler works in a pair with Looper, but i have some problem. I need to do some long operation in a back thread and then to send some result in a textView.
I get the following error after pressing a button:
Only the original thread that created a view hierarchy can touch its views.
public class MainActivity extends AppCompatActivity {
Button mButton;
TextView mTextView;
ConsumeThread mConsumeThread;
class ConsumeThread extends Thread{
public Handler mHandler;
#Override
public void run() {
Looper.prepare();
mHandler = new Handler(){
#Override
public void handleMessage(Message msg){
int arg = msg.what;
someLongOperation(arg);
}
};
Looper.loop();
}
private void someLongOperation(int arg){
// do some long operation
arg += 1000;
mTextView.setText("Operation's code is " +arg); // fatal exception
}
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextView = (TextView)findViewById(R.id.txt_view);
mButton = (Button) findViewById(R.id.button);
mConsumeThread = new ConsumeThread();
mConsumeThread.start();
mButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
if(mConsumeThread.mHandler != null){
Message msg = mConsumeThread.mHandler.obtainMessage(10);
mConsumeThread.mHandler.sendMessage(msg);
}
}
});
}
To get Main Thread Handler You have get Handler as follows .
Because:-
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
So you need to get Handler which is associated with MainThread. For that you can use one of the following:-
With Context
Handler mainHandler = new Handler(getMainLooper()){
#Override
public void handleMessage(Message msg) {
}
};
Or Directly with Looper even when do not have Context
Handler mainHandler = new Handler(Looper.getMainLooper()){
#Override
public void handleMessage(Message msg) {
}
};
I assume that you are doing some long running task . So its better if you go with AsyncTask.
private void someLongOperation(int arg){
// do some long operation
arg =+ 1000;
mTextView.setText("Operation's code is " +arg); // fatal exception
}
//see here, you are in worker thread, so you can't excess UI toolkit or else exception, so if you want to do something ui related task in worker thread, use runOnUi, see here
runOnUiThread(new Runnable() {
#Override
public void run() {
textview.setText("");
}
})
You can't update the UI from another thread. You have to move the code that updates the UI to the UIThread.
Try Using:
runOnUiThread(new Runnable() {
#Override
public void run() {
//TextView Update Code
}
});
Tip: Try to reduce the number of lines of code you put inside this, as then there would be no purpose of using another thread.
Only the original thread that created a view hierarchy can touch its views
You have to do ui related work on the main thread...
So you can do it like this...
private void someLongOperation(int arg){
// do some long operation
arg =+ 1000;
MainActivity.this.runOnUiThread(new Runnable() {
#Override
public void run() {
mTextView.setText("Operation's code is " +arg); // fatal exception
}
});
}
I have, to my knowledge, implemented a runnable which is created on a new thread. However, the thread does not seem to be running in the background, and the actions taken inside the runnable are stalling the UI with heavy actions.
See below:
custListLoadThread = new Thread(loadRunnable);
custListLoadThread.run();
private Runnable loadRunnable = new Runnable()
{
#Override
public void run()
{
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
Gen.popup("TEST"); // Creates a toast pop-up.
// This is to know if this runnable is running on UI thread or not!
try
{
customers = Db.BasicArrays.getCustomers(CustomApp.Session.businessCode, empId);
runOnUiThread(new Runnable() {
#Override
public void run() {
populate();
setCustListVisible(true);
loading = false;
}
});
}
catch (final Exception ex)
{
runOnUiThread(new Runnable() {
#Override
public void run() {
Gen.popup(ex.getMessage());
}
});
}
}
};
However this code does not run in the background, it still seems to run on the UI thread. I have placed the line Gen.popup("TEST"); to make sure of this (calling a toast pop up in a non-UI thread should cause an error).
Any ideas as to why this runnable isn't running in the background?
custListLoadThread = new Thread(loadRunnable);
custListLoadThread.start();
You need to start the thread, not call the run() method in the current thread.
If you want to execute code on a background thread that does not do something with the UI:
Runnable runnable = new Runnable() {
#Override
public void run() {
//your action
}
};
AsyncTask.execute(runnable);
Of course as written before you can also create a new thread (that is independent from the UI thread):
new Thread(runnable).start();
In your example you want to update UI elements, so better use a AsyncTask (must be called from UI thread!):
new AsyncTask<Void, Void, Void>() {
#Override
protected Void doInBackground(Void... params) {
// your async action
return null;
}
#Override
protected void onPostExecute(Void aVoid) {
// update the UI (this is executed on UI thread)
super.onPostExecute(aVoid);
}
}.execute();
I created a Looper thread class:
public class MyLooperThread extends Thread{
private Handler mHandler;
public void init(){
start(); //start the thread
synchronized (this) {
wait(5000); //wait for run()
}
Log.d("DEBUG","Init Done!");
//EXCEPTION: Can't create handler inside thread that has not called Looper.prepare()
MyObject obj = new MyObject(mHandler);
}
#Override
public void run() {
Looper.prepare();
mHandler = new Handler(){
#Override
public void handleMessage(Message msg){
//Check installed app package names, NOTHING RELATED WITH UI ...
}
};
synchronized (this) {
notify();
}
Looper.loop();
}//end of run()
}
In my Activity, I call above MyLooperThread 's init() method in onCreate(). Besides, I have a ToggleButton element, when ToggleButton is checked, I call MyLooperThread's init() method too.
public class MyActivity extends Activity implements OnCheckedChangeListener{
…
#Override
protected void onCreate(Bundle savedInstanceState){
…
myToggleButton.setOnCheckedChangeListener(this);
myToggleButton.setChecked(true);//checked by default
MyLooperThread myLooper = new MyLooperThread();
myLooper.init();
}
#Override
public void onCheckedChanged(CompoundButton button, boolean isChecked) {
if(isChecked){
MyLooperThread myLooper = new MyLooperThread();
myLooper.init();
}else{
...
}
}
}
When launch my app, it is fine. My toggle button is shown as checked by default. When I uncheck it & check it again, I got exception:
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
which is pointed to the init() method's last line of code MyObject obj = new MyObject(mHandler);
Why I got this exception? I don't understand, my mHandler is created after I called Looper.prepare() in run().
Pretty sure the error is saying you're trying to do something UI related when not on the UI thread.
As you haven't posted anything that you're doing inside the handleMessage, I'm gonna assume that you're trying to change one of the UI elements. Always use the UI thread to update the UI. It should go something like this:
handleMessage(Message msg) {
...
getActivity().runOnUiThread(new Runnable {
...
// update UI here
...
});
...
}
just use a HandlerThread():
ht = new HandlerThread();
ht.start();
h = new Handler(ht.getLooper());