android 设置系统屏幕亮度

关于亮度设置，网上有2种方式：设置系统亮度和设置当前Activity亮度。

1）设置Activity亮度
这个网上代码可以使用，本文就不说了。

2）设置系统亮度
试了网上的各种方案，都没有达到预期的效果。实际调试时，发现调节系统亮度时，亮度没有渐变效果，只是修改了系统的亮度值（就是设置后，去手机设置界面查看亮度，发现值已修改）。
后来参考了github上一个例子，它把1）和2）结合起来使用，达到成功设置系统亮度的效果。

即：滑动亮度滑块时，通过实时改变当前Activity亮度来实现亮度渐变效果，最后保存时再改变系统的亮度值。参考例子网址： https://github.com/malinkang/BrightnessDemo

本来以为一切都OK了，后来测试时发现：如果改变了Activity的亮度，再去手机设置里修改亮度，则对Activity无效。即：如果Activity设置了自己的亮度，则优先使用自己的亮度。未设置才会使用系统的亮度。

最后实现方式如下：滑动亮度滑块时，通过修改Activity亮度来达到亮度实时渐变的效果，点击确定后，则保存系统亮度，同时恢复Activity的亮度设置（值重置为-1）。

代码如下（项目用到了androidannotations library）：

/**
 * 系统亮度设置
 * 
 * @author qiw
 * @version 1.0, 2013-9-13
 */
@EBean(scope = Scope.Singleton)
public class BrightnessSettings {
    private static final String TAG = BrightnessSettings.class.getSimpleName();

    @RootContext
    Context context;

    /**
     * 获得当前系统的亮度模式
     * SCREEN_BRIGHTNESS_MODE_AUTOMATIC=1 为自动调节屏幕亮度
     * SCREEN_BRIGHTNESS_MODE_MANUAL=0 为手动调节屏幕亮度
     */
    public int getBrightnessMode() {
        int brightnessMode = Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL;
        try {
            brightnessMode = Settings.System.getInt(context.getContentResolver(),
                Settings.System.SCREEN_BRIGHTNESS_MODE);
        } catch (Exception e) {
            Log.e(TAG, "获得当前屏幕的亮度模式失败：", e);
        }
        return brightnessMode;
    }

    /**
     * 设置当前系统的亮度模式
     * SCREEN_BRIGHTNESS_MODE_AUTOMATIC=1 为自动调节屏幕亮度
     * SCREEN_BRIGHTNESS_MODE_MANUAL=0 为手动调节屏幕亮度
     */
    public void setBrightnessMode(int brightnessMode) {
        try {
            Settings.System.putInt(context.getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE, brightnessMode);
        } catch (Exception e) {
            Log.e(TAG, "设置当前屏幕的亮度模式失败：", e);
        }
    }

    /**
     * 获得当前系统的亮度值： 0~255
     */
    public int getSysScreenBrightness() {
        int screenBrightness = MAX_BRIGHTNESS;
        try {
            screenBrightness = Settings.System.getInt(context.getContentResolver(), Settings.System.SCREEN_BRIGHTNESS);
        } catch (Exception e) {
            Log.e(TAG, "获得当前系统的亮度值失败：", e);
        }
        return screenBrightness;
    }

    /**
     * 设置当前系统的亮度值:0~255
     */
    public void setSysScreenBrightness(int brightness) {
        try {
            ContentResolver resolver = context.getContentResolver();
            Uri uri = Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS);
            Settings.System.putInt(resolver, Settings.System.SCREEN_BRIGHTNESS, brightness);
            resolver.notifyChange(uri, null); // 实时通知改变
        } catch (Exception e) {
            Log.e(TAG, "设置当前系统的亮度值失败：", e);
        }
    }

    /**
     * 设置屏幕亮度，这会反映到真实屏幕上
     * 
     * @param activity
     * @param brightness
     */
    public void setActScreenBrightness(final Activity activity, final int brightness) {
        final WindowManager.LayoutParams lp = activity.getWindow().getAttributes();
        lp.screenBrightness = brightness / (float) MAX_BRIGHTNESS;
        activity.getWindow().setAttributes(lp);
    }

    /**
     * 显示调节亮度的设置对话框
     * 
     * @param act
     */
    public void showBrightnessSettingsDialog(final Activity act) {
        if (act == null) {
            return;
        }
        final int oldBrightness = getSysScreenBrightness(); // 当前系统的亮度
        final int oldBrightnessMode = getBrightnessMode(); // 当前系统的亮度模式
        boolean autoMode = (oldBrightnessMode == Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC); // 是否自动调节亮度模式
        LayoutInflater inflater = act.getLayoutInflater();
        View dialogLayout = inflater.inflate(R.layout.seekbar_dialog, null);
        CheckBox cbAutoMode = (CheckBox) dialogLayout.findViewById(R.id.cb_auto_mode); // 自动调节亮度
        cbAutoMode.setChecked(autoMode);
        final SeekBar seekbar = (SeekBar) dialogLayout.findViewById(R.id.seekbar); // 手动调节亮度
        int progress = oldBrightness - MIN_BRIGHTNESS; // SeekBar的值范围：0~225，代表的亮度值是30~255。
        seekbar.setProgress(progress < 0 ? 0 : progress);
        seekbar.setMax(MAX_BRIGHTNESS - MIN_BRIGHTNESS); // 最大值：225
        // 自动调节亮度选项改变时
        cbAutoMode.setOnCheckedChangeListener(new OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {
                    seekbar.setVisibility(View.GONE);
                    setBrightnessMode(Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC);
                } else {
                    seekbar.setVisibility(View.VISIBLE);
                    setBrightnessMode(Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);
                }
            }
        });
        // 手动调节亮度滑块滑动时
        seekbar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {
            }

            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                int brightness = progress + MIN_BRIGHTNESS; // 实际亮度
                // 亮度滑块滑动时，实时改变屏幕亮度
                setActScreenBrightness(act, brightness); // 改变当前屏幕亮度
                setSysScreenBrightness(brightness); // 改变系统屏幕亮度
            }
        });
        // 是否显示手动调节亮度滑块
        if (autoMode) {
            seekbar.setVisibility(View.GONE);
        }
        // 显示调节亮度的dialog
        AlertDialog.Builder builder = new AlertDialog.Builder(act);
        builder.setTitle(R.string.brightness_setting);
        builder.setView(dialogLayout);
        builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {
                // 点击确定按钮，恢复activity亮度设置
                setActScreenBrightness(act, -MAX_BRIGHTNESS);
            }
        });
        builder.setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {
                // 点击取消按钮，则需要还原亮度模式和亮度值的设置
                recoverBrightnessSetting(act, oldBrightnessMode, oldBrightness);
            }
        });
        builder.setOnCancelListener(new OnCancelListener() { // 点击返回键/dialog外部等让dialog消失的事件
            @Override
            public void onCancel(DialogInterface dialog) {
                recoverBrightnessSetting(act, oldBrightnessMode, oldBrightness);
            }
        });
        builder.show();
    }

    /**
     * 还原亮度模式和亮度值的设置
     * 
     * @param act
     * @param brightnessMode
     * @param brightness
     */
    private void recoverBrightnessSetting(final Activity act, final int brightnessMode, final int brightness) {
        setBrightnessMode(brightnessMode);
        setSysScreenBrightness(brightness);
        setActScreenBrightness(act, -MAX_BRIGHTNESS);
    }

    /** 可调节的最小亮度值 */
    public static final int MIN_BRIGHTNESS = 30;
    /** 可调节的最大亮度值 */
    public static final int MAX_BRIGHTNESS = 255;

}

调节亮度对话框布局文件（seekbar_dialog.xml）：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <CheckBox
        android:id="@+id/cb_auto_mode"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="@string/auto_brightness_setting"
        android:textSize="14sp" />

    <SeekBar
        android:id="@+id/seekbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/cb_auto_mode"
        android:max="225"
        android:paddingBottom="10dp" />

</RelativeLayout>

实际效果截图：