The class Handler can update the UI. A handle provides methods for receiving messages and for runnables. To use a handler you have to subclass it and overide handleMessage () to process messages. To process runables you can use the method post (); you only need one instance of a handler in your activity.
Your thread can post messages via the method sendMessage (Message msg) or sendEmptyMessage.
In this article I am going to explain how to create a handler in an Android application. In this example I will use the class Handler to update a ProgressBar in a background thread.
- Start a new project named HandlerDemo.
- Open res/values/strings.xml and add the following strings element in the resource tag:
<string name="startProgress">startProgress</string>
- Open res/layout/main.xml and insert the following code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ProgressBar android:id="@+id/progressBar1"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:indeterminate="false"
android:max="10" android:padding="4dip">
</ProgressBar>
<Button android:text="Start Progress"
android:onClick="startProgress"
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</Button>
</LinearLayout>
· Now open the Activity file and insert the following code:
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;
public class HandlerActivity extends Activity {
private Handler handler;
private ProgressBar progress;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
progress = (ProgressBar) findViewById(R.id.progressBar1);
handler = new Handler();
}
public void startProgress(View view) {
Runnable runnable = new Runnable() {
public void run() {
for (int i = 0; i <= 10; i++) {
final int value = i;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
handler.post(new Runnable() {
public void run() {
progress.setProgress(value);
}
});
}
}
};
new Thread(runnable).start();
}
}
· Run the application.
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