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Using Handler for long-time operations in Android


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Need to notify user when for example user clicks button and in onClick method program starts some long-time process. Need to have some solution which will do your task in background. Handler is very good solution for this problem.

If you will not use such approach then user will see that program appears to hang.

How to use it.

First need to to override handleMessage method.

private Handler handler = new Handler() {

@Override

public void handleMessage(Message msg) {

super.handleMessage(msg);

// do something

}

};

At second need to create Thread.

new Thread() {

public void run() {

//long time method

handler.sendEmptyMessage(0);

}

}.start();

I will post whole code for showing whole picture.

Example:

package com.faynasoftlabs.tutorial.android.handlerexample;

import android.app.Activity;

import android.app.ProgressDialog;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.util.Log;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

/**

* Class which shows how to work with handler class

* @author FaYna Soft Labs

*/

public class Main extends Activity {

private Button clickBtn;

private ProgressDialog progressDialog;

private Handler handler = new Handler() {

@Override

public void handleMessage(Message msg) {

super.handleMessage(msg);

progressDialog.dismiss();

}

};

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

clickBtn = (Button) findViewById(R.id.click);

clickBtn.setText("Click me");

clickBtn.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

processThread();

}

});

}

private void processThread() {

progressDialog = ProgressDialog.show(Main.this, "", "Doing...");

new Thread() {

public void run() {

longTimeMethod();

handler.sendEmptyMessage(0);

}

}.start();

}

private void longTimeMethod() {

try {

Thread.sleep(10000);

} catch (InterruptedException e) {

Log.e("tag", e.getMessage());

}

}

}

Using Handler is very useful and easy. If you will follow this practice your users will not see that your program appears to hang.

But in Android 1.5 and higher versions there is better approach. AsyncTask class is more preferred. How to use AsyncTask I will show next time.

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Categories: Android, Android how to
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