Using Handler in Android Application
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.
The output looks like below:
When you click on the Start Progress button, progress bar will start and looks
like below:
