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POWhy use Handler?
 

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    <p>I came across this code in a very basic Handler tutorial. The code is working fine but I do not understand why I have to use Handler for <code>progressDialog.dismiss()</code> ??? I removed the Handler part and placed <code>progressDialog.dismiss()</code> in the <code>run()</code> method and it worked fine. So why used Handler???</p> <pre><code> import android.app.Activity; import android.app.ProgressDialog; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; public class HandlerThread extends Activity{ private Button start; private ProgressDialog progressDialog; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); start = (Button) findViewById(R.id.Button01); start.setOnClickListener(new OnClickListener() { @Override public void onClick(View arg0) { // TODO Auto-generated method stub fetchData(); } }); } protected void fetchData() { // TODO Auto-generated method stub progressDialog = ProgressDialog.show(this, "", "Doing..."); new Thread() { public void run() { try { Thread.sleep(8000); } catch (InterruptedException e) { } messageHandler.sendEmptyMessage(0); } }.start(); } private Handler messageHandler = new Handler() { public void handleMessage(Message msg) { super.handleMessage(msg); progressDialog.dismiss(); } }; } </code></pre>
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    1. USSyamantak Basu
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      1. USVirag Brahme
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    1. COSomething wrong with your observation. Calling progressDialog.dismiss() inside run() method, which is running on a non-UI thread, will throw an exception.
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      1. USSameer
    2. CO@Sameer not necessarily. See [my answer](http://stackoverflow.com/a/12313049/165674).
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      1. USDheeraj V.S.
    3. COsimply you cannot change state of any view from working (or background) thread. Only from `UI` thread you can change it so for this approach is usually used `Handler` or `AsyncTask`
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      1. USSimon Dorociak
 

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