控件：拖动条 SeekBar（改变屏幕亮度）

<?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">
    <ImageView 
        android:id="@+id/pic"
        android:src="@drawable/android_book"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/> 
    <SeekBar 
        android:id="@+id/seekbar" 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

import android.app.Activity;
import android.os.Bundle;
import android.view.WindowManager;
import android.widget.SeekBar;

public class MySeekBarDemo extends Activity {
    private SeekBar seekbar = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        super.setContentView(R.layout.main);
        this.seekbar = (SeekBar) super.findViewById(R.id.seekbar);  
        this.seekbar.setMax(100);
        this.seekbar.setOnSeekBarChangeListener(new OnSeekBarChangeListenerImpl());
    }

    private class OnSeekBarChangeListenerImpl implements SeekBar.OnSeekBarChangeListener {
        @Override
        public void onStartTrackingTouch(SeekBar seekBar) {
        }
        @Override
        public void onProgressChanged(SeekBar seekBar, int progress,boolean fromUser) {
            MySeekBarDemo.this.setScreenBrightness((float) seekBar.getProgress() / 100);
        }
        @Override
        public void onStopTrackingTouch(SeekBar seekBar) {
        }
    }
    /**
     * WindowManager.LayoutParams可以进行屏幕亮度调节
     * @param num
     */
    private void setScreenBrightness(float num) {    // 0 ~ 1表示亮度
        // 取得屏幕的属性
        WindowManager.LayoutParams layoutParams = super.getWindow().getAttributes() ;    
        // 设置屏幕亮度
        layoutParams.screenBrightness = num ;    
        // 重新设置窗口的属性
        super.getWindow().setAttributes(layoutParams) ;    
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="org.lxh.demo"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="3" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
    
        <activity android:name=".MySeekBarDemo"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
</manifest>