I'm trying to use the UI-Thread, so I've written a simple test activity. But I think I've misunderstood something, because on clicking the button - the app does not respond anymore
public class TestActivity extends Activity {
Button btn;
int i = 0;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btn = (Button)findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
runThread();
}
});
}
private void runThread(){
runOnUiThread (new Thread(new Runnable() {
public void run() {
while(i++ < 1000){
btn.setText("#"+i);
try {
Thread.sleep(300);
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}));
}
}
Below is corrected Snippet of runThread Function.
private void runThread() {
new Thread() {
public void run() {
while (i++ < 1000) {
try {
runOnUiThread(new Runnable() {
#Override
public void run() {
btn.setText("#" + i);
}
});
Thread.sleep(300);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}.start();
}
Just wrap it as a function, then call this function from your background thread.
public void debugMsg(String msg) {
final String str = msg;
runOnUiThread(new Runnable() {
#Override
public void run() {
mInfo.setText(str);
}
});
}
You have it back-to-front. Your button click results in a call to runOnUiThread(), but this isn't needed, since the click handler is already running on the UI thread. Then, your code in runOnUiThread() is launching a new background thread, where you try to do UI operations, which then fail.
Instead, just launch the background thread directly from your click handler. Then, wrap the calls to btn.setText() inside a call to runOnUiThread().
runOnUiThread(new Runnable() {
public void run() {
//Do something on UiThread
}
});
There are several techniques using of runOnUiThread(), lets see all
This is my main thread (UI thread) called AndroidBasicThreadActivity and I'm going to update it from a worker thread in various ways -
public class AndroidBasicThreadActivity extends AppCompatActivity
{
public static TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_android_basic_thread);
textView = (TextView) findViewById(R.id.textview);
MyAndroidThread myTask = new MyAndroidThread(AndroidBasicThreadActivity.this);
Thread t1 = new Thread(myTask, "Bajrang");
t1.start();
}
}
1.) By passing Activity's instance as an argument on worker thread
class MyAndroidThread implements Runnable
{
Activity activity;
public MyAndroidThread(Activity activity)
{
this.activity = activity;
}
#Override
public void run()
{
//perform heavy task here and finally update the UI with result this way -
activity.runOnUiThread(new Runnable()
{
#Override
public void run()
{
AndroidBasicThreadActivity.textView.setText("Hello!! Android Team :-) From child thread.");
}
});
}
}
2.) By using View's post(Runnable runnable) method in worker thread
class MyAndroidThread implements Runnable
{
Activity activity;
public MyAndroidThread(Activity activity)
{
this.activity = activity;
}
#Override
public void run()
{
//perform heavy task here and finally update the UI with result this way -
AndroidBasicThreadActivity.textView.post(new Runnable()
{
#Override
public void run()
{
AndroidBasicThreadActivity.textView.setText("Hello!! Android Team :-) From child thread.");
}
});
}
}
3.) By using Handler class from android.os package
If we don't have the context (this/ getApplicationContext()) or Activity's instance (AndroidBasicThreadActivity.this) then we have to use Handler class as below -
class MyAndroidThread implements Runnable
{
Activity activity;
public MyAndroidThread(Activity activity)
{
this.activity = activity;
}
#Override
public void run()
{
//perform heavy task here and finally update the UI with result this way -
new Handler(Looper.getMainLooper()).post(new Runnable() {
public void run() {
AndroidBasicThreadActivity.textView.setText("Hello!! Android Team :-) From child thread.");
}
});
}
}
If using in fragment then simply write
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
// Do something on UiThread
}
});
We use Worker Thread to make Apps smoother and avoid ANR's. We may need to update UI after the heavy process in worker Tread.
The UI can only be updated from UI Thread. In such cases, we use Handler or runOnUiThread both have a Runnable run method that executes in UI Thread.
The onClick method runs in UI thread so don't need to use runOnUiThread here.
Using Kotlin
While in Activity,
this.runOnUiThread {
// Do stuff
}
From Fragment,
activity?.runOnUiThread {
// Do stuff
}
Using Java,
this.runOnUiThread(new Runnable() {
void run() {
// Do stuff
}
});
For fragment use that:
requireActivity().runOnUiThread(() -> {
//your code logic
});
For activity use that:
runOnUiThread(() -> {
//your code logic
});
runOnUiThread is used in a way the UI can be updated with our background thread. For more: https://www.tutorialspoint.com/how-do-we-use-runonuithread-in-android
thy this:
#UiThread
public void logMsg(final String msg) {
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
Log.d("UI thread", "I am the UI thread");
}
});
}
You can use from this sample :
In the following example, we are going to use this facility to publish the result from a
synonym search that was processed by a background thread.
To accomplish the goal during the OnCreate activity callback, we will set up
onClickListener to run searchTask on a created thread.
When the user clicks on the Search button, we will create a Runnable anonymous
class that searches for the word typed in R.id.wordEt EditText and starts the
thread to execute Runnable.
When the search completes, we will create an instance of Runnable SetSynonymResult
to publish the result back on the synonym TextView over the UI thread.
This technique is sometime not the most convenient one, especially when we don't
have access to an Activity instance; therefore, in the following chapters, we are
going to discuss simpler and cleaner techniques to update the UI from a background
computing task.
public class MainActivity extends AppCompatActivity {
class SetSynonymResult implements Runnable {
String synonym;
SetSynonymResult(String synonym) {
this.synonym = synonym;
}
public void run() {
Log.d("AsyncAndroid", String.format("Sending synonym result %s on %d",
synonym, Thread.currentThread().getId()) + " !");
TextView tv = (TextView) findViewById(R.id.synonymTv);
tv.setText(this.synonym);
}
}
;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button search = (Button) findViewById(R.id.searchBut);
final EditText word = (EditText) findViewById(R.id.wordEt);
search.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Runnable searchTask = new Runnable() {
#Override
public void run() {
String result = searchSynomim(word.getText().toString());
Log.d("AsyncAndroid", String.format("Searching for synonym for %s on %s",
word.getText(), Thread.currentThread().getName()));
runOnUiThread(new SetSynonymResult(result));
}
};
Thread thread = new Thread(searchTask);
thread.start();
}
});
}
static int i = 0;
String searchSynomim(String word) {
return ++i % 2 == 0 ? "fake" : "mock";
}
}
Source :
asynchronous android programming Helder Vasconcelos
This is how I use it:
runOnUiThread(new Runnable() {
#Override
public void run() {
//Do something on UiThread
}
});
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
gifImageView = (GifImageView) findViewById(R.id.GifImageView);
gifImageView.setGifImageResource(R.drawable.success1);
new Thread(new Runnable() {
#Override
public void run() {
try {
//dummy delay for 2 second
Thread.sleep(8000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//update ui on UI thread
runOnUiThread(new Runnable() {
#Override
public void run() {
gifImageView.setGifImageResource(R.drawable.success);
}
});
}
}).start();
}
Try this: getActivity().runOnUiThread(new Runnable...
It's because:
1) the implicit this in your call to runOnUiThread is referring to AsyncTask, not your fragment.
2) Fragment doesn't have runOnUiThread.
However, Activity does.
Note that Activity just executes the Runnable if you're already on the main thread, otherwise it uses a Handler. You can implement a Handler in your fragment if you don't want to worry about the context of this, it's actually very easy:
// A class instance
private Handler mHandler = new Handler(Looper.getMainLooper());
// anywhere else in your code
mHandler.post(<your runnable>);
// ^ this will always be run on the next run loop on the main thread.
Related
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 want to save data to DB in new Thread and after that show toast on the UI.
Method for saving:
public void addToBasket(String text) {
new Thread(() -> {
//emulate save
try {
Thread.sleep(5000L);
} catch (InterruptedException e) {
e.printStackTrace();
}
//after that I need say ti UI thread - show Toast!
}).start();
}
I call this method:
BasketService.me().addToBasket(result.getContents());
I do now want use AsyncTask for this. Please tell me the best way to implement such tasks
batter to use:
runOnUiThread(new Runnable() {
public void run() {
//Do what ever you want do man
}
});
runOnUiThread() method to manipulate your UserInterface from background threads.
In case of callback from a nonUi thread to Ui thread you can use runOnUiThread()(As specified above) or Handler. Below is a example of using handler.
protected static final Handler mainThreadHandler = new Handler(Looper.getMainLooper());
protected void onSuccessInMainThread(final R result, final Bundle bundle) {
mainThreadHandler.post(new Runnable() {
#Override
public void run() {
callback.onSuccess(result, bundle);
}
});
}
protected void onErrorInMainThread(final Exception error) {
mainThreadHandler.post(new Runnable() {
#Override
public void run() {
callback.onError(error);
}
});
}
Can I create onClickListener() for a button in more than 1 threads that are executing simultaneously?
Would that listener be called individually in every thread?
No, a button has only one onClickListener. Setting a second one overwrites any listener set previously. And that function will only be called on the UI thread. You can pass messages to multiple threads from that function though.
There are a lot of ways to communicate between threads. Since you are wondering how to pass something over to the thread, here is a simple example:
public class MainActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
...
//Start a thread you need to
anotherThread = new AnotherThread();
anotherThread.start();
}
protected void onResume() {
...
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
anotherThread.sendData(message);
}
});
}
}
public class AnotherThread extends Thread {
//Instantiate handler to associate it with the current thread.
//Handler enqueues all tasks in the MessageQueue using Looper
//and execute them upon coming out of queue;
private Handler handler;
#Override
public void run() {
try {
//Here we create a unique Looper for this thread.
//The main purpose of which to keep thread alive looping through
//MessageQueue and send task to corresponding handler.
Looper.prepare();
handler = new Handler() {
#Override
public void handleMessage(Message msg) {
//manage incoming messages here
String value = msg.getData().getString("key");
}
};
Looper.loop();
} catch (Throwable e) {
e.printStackTrace();
}
}
public synchronized void sendData(Message message) {
handler.post(new Runnable() {
#Override
public void run() {
handler.sendMessage(message);
}
});
}
}
To get more about thread communication I'd recommend you the following:
1, 2, 3.
I thought that it is not possible to access main thread views in a new thread!
But why below codes runs without any problem?!
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textView);
new Thread(new Runnable() {
#Override
public void run() {
try {
textView.append(InetAddress.getByName("192.168.1.252").getHostName() + "\n\n");
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
}).start();
}
As it stands here:
For example, below is some code for a click listener that downloads an
image from a separate thread and displays it in an ImageView:
public void onClick(View v) {
new Thread(new Runnable() {
public void run() {
Bitmap b = loadImageFromNetwork("http://example.com/image.png");
mImageView.setImageBitmap(b);
}
}).start();
}
At first, this seems to work fine, because it creates a new thread to
handle the network operation. However, it violates the second rule of
the single-threaded model: do not access the Android UI toolkit from
outside the UI thread—this sample modifies the ImageView from the
worker thread instead of the UI thread. This can result in undefined
and unexpected behavior, which can be difficult and time-consuming to
track down.
So it works, but not recommended.
There are some recommended way to do this instead:
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)
try this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textView);
new Thread(new Runnable() {
#Override
public void run() {
try {
runOnUiThread(new Runnable() {
#Override
public void run() {
textView.append(InetAddress.getByName("192.168.1.252").getHostName() + "\n\n");
}
});
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
}).start();
}
runOnUiThread - is method from activity. if you work inside fragment you can call getActivity().runOnUiThread
The solution is to run the UI thread inside your new thread.
Here is an example using anko.
btn_login.text = "LOGING IN"
doAsync {
authenticate(email, password)
uiThread { btn_login.text = "LOGIN" }
}
Android recommend update ui in the ui thread,but i found that i can update the ui in the non-ui thread directly like below:
public class MainActivity extends Activity {
private TextView textView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
new Thread(new Runnable() {
#Override
public void run() {
textView.setText("SecondThread");
}
}).start();
}
}
That's run correctly,but if i sleep the thread 1000ms:
public class MainActivity extends Activity {
private TextView textView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
new Thread(new Runnable() {
#Override
public void run() {
try {
**Thread.sleep(1000);**
} catch (InterruptedException e) {
e.printStackTrace();
}
textView.setText("SecondThread");
}
}).start();
}
}
I get the error"Only the original thread that created a view hierarchy can touch its views",i try to change the sleep value much times,i found when i set the value 135 or less,it can run correctly：
Thread.sleep(135);
Thread.sleep(134);
Thread.sleep(...);
That's very interesting!But why it happen?I can't find any way to make sense of that,is anyone can help me?thanks!
If you are trying to touch views from background thread you should consider using runOnUiThread method, which accepts runnable as argument in which you can update views
EDIT: Also I would recommed you to use AsyncTask to achieve your goals, it has two callbacks onPreExecute and onPostExecute, whiche are invoked on the UI thread
so will always work
new Thread(new Runnable() {
#Override
public void run() {
try {
**Thread.sleep(1000);**
} catch (InterruptedException e) {
e.printStackTrace();
}
runOnUiThread(new Runable(){
#Override
public void run(){
textView.setText("SecondThread");
});
}
}).start();
There is another way to use the Handler()