当执行某些正在处理的任务时，ProgressBar提供了一个可视化的反溃例如，你在从web服务器下载数据，然后需要更新下载的状态。在这种情况下，ProgressBar就是一个很好的选择。下面的例子，展示如何去使用ProgressBar。
1、创建一个工程，BasicViews2。
2、main.xml中的代码。
[html]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ProgressBar android:id="@+id/progressbar"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
3、Basic2Activity.java中的代码。
[java]
package net.learn2develop.BasicViews2;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;
public class BasicViews2Activity extends Activity {
static int progress;
ProgressBar progressBar;
int progressStatus = 0;
Handler handler = new Handler();
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
progress = 0;
progressBar = (ProgressBar) findViewById(R.id.progressbar);
//---do some work in background thread---
new Thread(new Runnable()
{
public void run()
{
//?do some work here?
while (progressStatus < 10)
{
progressStatus = doSomeWork();
}
//---hides the progress bar---
handler.post(new Runnable()
{
public void run()
{
//---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE---
progressBar.setVisibility(View.GONE);
}
});
}
//---do some long running work here---
private int doSomeWork()
{
try {
//---simulate doing some work---
Thread.sleep(500);
} catch (InterruptedException e)
{
e.printStackTrace();
}
return ++progress;
}
}).start();
}
}
4、F11调试，会看见ProgressBar的动画，5秒之后，动画消失。
接下来展示如何自定义ProgressBar的样式。
1、使用之前的例子，修改main.xml。
[html]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ProgressBar android:id="@+id/progressbar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="@android:style/Widget.ProgressBar.Horizontal" />
</LinearLayout>
2、Basic2Activity.java中的代码。
[java]
package net.learn2develop.BasicViews2;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ProgressBar;
public class BasicViews2Activity extends Activity {
static int progress;
ProgressBar progressBar;
int progressStatus = 0;
Handler handler = new Handler();
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
progress = 0;
progressBar = (ProgressBar) findViewById(R.id.progressbar);
progressBar.setMax(200);
//---do some work in background thread---
new Thread(new Runnable()
{
public void run()
{
//?do some work here?
while (progressStatus < 100)
{
progressStatus = doSomeWork();
//?Update the progress bar?
handler.post(new Runnable()
{
public void run() {
progressBar.setProgress(progressStatus);
}
});
}
//---hides the progress bar---
handler.post(new Runnable()
{
public void run()
{
//---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE---
progressBar.setVisibility(View.GONE);
}
});
}
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//---do some long running work here---
private int doSomeWork()
{
try {
//---simulate doing some work---
Thread.sleep(50);
} catch (InterruptedException e)
{
e.printStackTrace();
}
return ++progress;
}
}).start();
}
}
3、F11调试。
4、当ProgressBar的进度到达50%的时候，它就会消失。
附：
ProgressBar的样式列表。
Widget.ProgressBar.Horizontal
Widget.ProgressBar.Small
Widget.ProgressBar.Large
Widget.ProgressBar.Inverse
Widget.ProgressBar.Small.Inverse
Widget.ProgressBar.Large.Inverse
