Android 获取和设置屏幕亮度的模式和值

最近有一个需求，是要能够设置Android的屏幕的亮度的模式和值。简单来说，就是把原生设置里面就有的功能再用自己的UI做一遍。OK，接下来就是查看源码。首先找到显示的java类，是在setting包下面的DisplaySettings.java。

package com.android.settings;public class DisplaySettings extends SettingsPreferenceFragment implements        Preference.OnPreferenceChangeListener, OnPreferenceClickListener {    private static final String TAG = "DisplaySettings";

很明显,它是的preferenceFragment。那么，我们看看它的xml文件。定位亮度对应的preference

    <!-- 亮度-->        <com.android.settings.BrightnessPreference                android:title="@string/brightness"                android:persistent="false"/>

接着打开BrightnessPrefere。

public class BrightnessPreference extends Preference {    public BrightnessPreference(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    protected void onClick() {            Intent intent = new Intent(Intent.ACTION_SHOW_BRIGHTNESS_DIALOG);        getContext().sendBroadcastAsUser(intent, UserHandle.CURRENT_OR_SELF);    }}

很简单的逻辑，只是发送一个广播，那么，是谁来接受处理呢？就是SystemUI。    这里是一个自定义的Dialog，我们接着追踪代码。BrightnessDialog的代码很简单。就是自定义ContentView，重点是通过BrightnessControler来处理逻辑。

    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        Window window = getWindow();        window.setType(WindowManager.LayoutParams.TYPE_VOLUME_OVERLAY);        window.getAttributes().privateFlags |=                WindowManager.LayoutParams.PRIVATE_FLAG_SHOW_FOR_ALL_USERS;        window.clearFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);        window.requestFeature(Window.FEATURE_NO_TITLE);        setContentView(R.layout.quick_settings_brightness_dialog);        setCanceledOnTouchOutside(true);    }    @Override    protected void onStart() {        super.onStart();        mBrightnessController = new BrightnessController(getContext(),                (ImageView) findViewById(R.id.brightness_icon),                (ToggleSlider) findViewById(R.id.brightness_slider));        dismissBrightnessDialog(mBrightnessDialogLongTimeout);        mBrightnessController.addStateChangedCallback(this);    }

好了，终于找到处理的地方，接下来就是看懂他们

/* * Copyright (C) 2013 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.android.systemui.settings;import android.content.ContentResolver;import android.content.Context;import android.database.ContentObserver;import android.net.Uri;import android.os.AsyncTask;import android.os.Handler;import android.os.IPowerManager;import android.os.PowerManager;import android.os.RemoteException;import android.os.ServiceManager;import android.os.UserHandle;import android.provider.Settings;import android.provider.Settings.SettingNotFoundException;import android.widget.ImageView;import java.util.ArrayList;public class BrightnessController implements ToggleSlider.Listener {    private static final String TAG = "StatusBar.BrightnessController";    private final int mMinimumBacklight;    private final int mMaximumBacklight;    private final Context mContext;    private final ImageView mIcon;    private final ToggleSlider mControl;    private final boolean mAutomaticAvailable;    private final IPowerManager mPower;    private final CurrentUserTracker mUserTracker;    private final Handler mHandler;    private final BrightnessObserver mBrightnessObserver;    private ArrayList<BrightnessStateChangeCallback> mChangeCallbacks =            new ArrayList<BrightnessStateChangeCallback>();    public interface BrightnessStateChangeCallback {        public void onBrightnessLevelChanged();    }    /** ContentObserver to watch brightness **/    private class BrightnessObserver extends ContentObserver {        private final Uri BRIGHTNESS_MODE_URI =                Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS_MODE);        private final Uri BRIGHTNESS_URI =                Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS);        public BrightnessObserver(Handler handler) {            super(handler);        }        @Override        public void onChange(boolean selfChange) {            onChange(selfChange, null);        }        @Override        public void onChange(boolean selfChange, Uri uri) {            if (selfChange) return;            if (BRIGHTNESS_MODE_URI.equals(uri)) {                updateMode();            } else if (BRIGHTNESS_URI.equals(uri)) {                updateSlider();            } else {                updateMode();                updateSlider();            }            for (BrightnessStateChangeCallback cb : mChangeCallbacks) {                cb.onBrightnessLevelChanged();            }        }        public void startObserving() {            final ContentResolver cr = mContext.getContentResolver();            cr.unregisterContentObserver(this);            cr.registerContentObserver(                    BRIGHTNESS_MODE_URI,                    false, this, UserHandle.USER_ALL);            cr.registerContentObserver(                    BRIGHTNESS_URI,                    false, this, UserHandle.USER_ALL);        }        public void stopObserving() {            final ContentResolver cr = mContext.getContentResolver();            cr.unregisterContentObserver(this);        }    }    public BrightnessController(Context context, ImageView icon, ToggleSlider control) {        mContext = context;        mIcon = icon;        mControl = control;        mHandler = new Handler();        mUserTracker = new CurrentUserTracker(mContext) {            @Override            public void onUserSwitched(int newUserId) {                updateMode();                updateSlider();            }        };        mBrightnessObserver = new BrightnessObserver(mHandler);        mBrightnessObserver.startObserving();        PowerManager pm = (PowerManager)context.getSystemService(Context.POWER_SERVICE);        mMinimumBacklight = pm.getMinimumScreenBrightnessSetting();        mMaximumBacklight = pm.getMaximumScreenBrightnessSetting();        mAutomaticAvailable = context.getResources().getBoolean(                com.android.internal.R.bool.config_automatic_brightness_available);        mPower = IPowerManager.Stub.asInterface(ServiceManager.getService("power"));        // Update the slider and mode before attaching the listener so we don't receive the        // onChanged notifications for the initial values.        updateMode();        updateSlider();        control.setOnChangedListener(this);    }    public void addStateChangedCallback(BrightnessStateChangeCallback cb) {        mChangeCallbacks.add(cb);    }    public boolean removeStateChangedCallback(BrightnessStateChangeCallback cb) {        return mChangeCallbacks.remove(cb);    }    @Override    public void onInit(ToggleSlider control) {        // Do nothing    }    /** Unregister all call backs, both to and from the controller */    public void unregisterCallbacks() {        mBrightnessObserver.stopObserving();        mChangeCallbacks.clear();        mUserTracker.stopTracking();    }    public void onChanged(ToggleSlider view, boolean tracking, boolean automatic, int value) {        setMode(automatic ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC                : Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);        updateIcon(automatic);        if (!automatic) {            final int val = value + mMinimumBacklight;            setBrightness(val);            if (!tracking) {                AsyncTask.execute(new Runnable() {                        public void run() {                            Settings.System.putIntForUser(mContext.getContentResolver(),                                    Settings.System.SCREEN_BRIGHTNESS, val,                                    UserHandle.USER_CURRENT);                        }                    });            }        }        for (BrightnessStateChangeCallback cb : mChangeCallbacks) {            cb.onBrightnessLevelChanged();        }    }    private void setMode(int mode) {        Settings.System.putIntForUser(mContext.getContentResolver(),                Settings.System.SCREEN_BRIGHTNESS_MODE, mode,                mUserTracker.getCurrentUserId());    }    private void setBrightness(int brightness) {        try {            mPower.setTemporaryScreenBrightnessSettingOverride(brightness);        } catch (RemoteException ex) {        }    }    private void updateIcon(boolean automatic) {        if (mIcon != null) {            mIcon.setImageResource(automatic ?                    com.android.systemui.R.drawable.ic_qs_brightness_auto_on :                    com.android.systemui.R.drawable.ic_qs_brightness_auto_off);        }    }    /** Fetch the brightness mode from the         system settings and * update the icon         更新亮度的你模式    */    private void updateMode() {        if (mAutomaticAvailable) {            int automatic;            try {                automatic = Settings.System.getIntForUser(mContext.getContentResolver(),                        Settings.System.SCREEN_BRIGHTNESS_MODE,                        UserHandle.USER_CURRENT);            } catch (SettingNotFoundException snfe) {                automatic = 0;            }            mControl.setChecked(automatic != 0);            updateIcon(automatic != 0);        } else {            mControl.setChecked(false);            updateIcon(false /*automatic*/);        }    }    /** Fetch the brightness from the system settings and update the slider     更新亮度的值*/    private void updateSlider() {        int value;        try {            value = Settings.System.getIntForUser(mContext.getContentResolver(),                    Settings.System.SCREEN_BRIGHTNESS,                    UserHandle.USER_CURRENT);        } catch (SettingNotFoundException ex) {            value = mMaximumBacklight;        }        mControl.setMax(mMaximumBacklight - mMinimumBacklight);        mControl.setValue(value - mMinimumBacklight);    }}

代码逻辑不难，可以从构造方法开始看起。注册了一个观察者， 然后通过读取和设置来对屏幕的亮度值和模式修改。