Android 获取和设置屏幕亮度的模式和值_android app打开屏幕亮度ui

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。
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package com.android.settings;

public class DisplaySettings extends SettingsPreferenceFragment implements
        Preference.OnPreferenceChangeListener, OnPreferenceClickListener {
    private static final String TAG = "DisplaySettings";
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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
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    <!-- 亮度-->
        <com.android.settings.BrightnessPreference
                android:title="@string/brightness"
                android:persistent="false"/>
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接着打开BrightnessPrefere。
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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);
    }
}
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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。
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    @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);
    }
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好了，终于找到处理的地方，接下来就是看懂他们
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/*
 * 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);
    }
}
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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。