android 改变app亮度不影响系统亮度（获取系统亮度）

在做改变亮度的时候基本都是改变系统的亮度，那如何改变app亮度又不影响系统亮度呢？在app上改变亮度后，退出app亮度恢复成系统原先的亮度，但是在次进入app的时候，亮度还要恢复成app当初设置的亮度。
需要demo的拉倒底部可以下载。
代码：
布局文件
activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent" >    <SeekBar        android:id="@+id/seekBar1"        android:layout_width="match_parent"        android:layout_height="wrap_content"        style="@style/Widget.SeekBar.Normal"        android:layout_marginTop="124dp" /></RelativeLayout>

values文件夹下的style文件
style.xml

<style name="Widget.SeekBar.Normal"  parent="@android:style/Widget.SeekBar">        <item name="android:maxHeight">8.0dip</item>        <item name="android:indeterminateOnly">false</item>        <item name="android:indeterminateDrawable">@android:drawable/progress_indeterminate_horizontal</item>        <item name="android:progressDrawable">@drawable/seekbar_horizontal</item>        <item name="android:minHeight">8.0dip</item>        <item name="android:thumb">@drawable/seek_thumb</item>        <item name="android:thumbOffset">10.0dip</item>    </style>

在res文件夹下创建一个drawable文件夹，里面放：
seekbar_horizontal.xml

<?xml version="1.0" encoding="UTF-8"?><layer-list  xmlns:android="http://schemas.android.com/apk/res/android">    <item android:id="@android:id/background" android:drawable="@drawable/seek_bkg" />    <item android:id="@android:id/secondaryProgress">        <clip>            <shape>                <corners android:radius="2.0dip" />                <gradient android:startColor="#80ffd300" android:endColor="#a0ffcb00" android:angle="270.0" android:centerY="0.75" android:centerColor="#80ffb600" />            </shape>        </clip>    </item>    <item android:id="@android:id/progress">        <clip android:drawable="@drawable/seek" />    </item></layer-list>

主activity
MainActivity.java

package com.example.liangdu;import android.app.Activity;import android.content.ContentResolver;import android.content.SharedPreferences;import android.content.SharedPreferences.Editor;import android.os.Bundle;import android.provider.Settings;import android.provider.Settings.SettingNotFoundException;import android.view.Window;import android.view.WindowManager;import android.widget.SeekBar;public class MainActivity extends Activity {    private SeekBar seekBar;    private SharedPreferences shared = null;    private int num=0;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        seekBar = (SeekBar) findViewById(R.id.seekBar1);        shared=getSharedPreferences("base64",MODE_PRIVATE);        num=shared.getInt("seekBarNum", 0);        changeAppBrightness(num);        seekBar.setProgress(num);        seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {            @Override            public void onStopTrackingTouch(SeekBar seekBar) {                // TODO Auto-generated method stub                /* 结束 */            }            @Override            public void onStartTrackingTouch(SeekBar seekBar) {                // TODO Auto-generated method stub                /* 开始 */            }            @Override            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {                // TODO Auto-generated method stub                changeAppBrightness(seekBar.getProgress());            }        });    }    // 获取系统屏幕亮度    public int getScreenBrightness() {        int value = 0;        ContentResolver cr = getContentResolver();        try {            value = Settings.System.getInt(cr, Settings.System.SCREEN_BRIGHTNESS);        } catch (SettingNotFoundException e) {        }        return value;    }    // 获取app亮度    public void changeAppBrightness(int brightness) {        Window window = getWindow();        WindowManager.LayoutParams lp = window.getAttributes();        lp.screenBrightness = (brightness <= 0 ? 1 : brightness) / 255f;        window.setAttributes(lp);    }    @Override    protected void onStop() {        // TODO Auto-generated method stub        super.onStop();        Editor editor=  shared.edit();        editor.clear();        editor.putInt("seekBarNum", seekBar.getProgress());        editor.commit();    }}

Editor 保存操作我是放在了生命周期onStop（）方法里，因为每次退出都要保存当前seekBar的值。
源码demo：http://download.csdn.net/detail/qq_17299423/9527147