// 获得摄像头的数量，前置和后置

getPreferredCameraId();

// 获得对焦设置eg：连续对焦或者其它

String[] defaultFocusModes = getResources().getStringArray(R.array.pref_camera_focusmode_default_array);

//实例化Focus管理对象

mFocusManager = new FocusManager(mPreferences, defaultFocusModes);

// 开启线程来启动摄像头

mCameraOpenThread.start();

// 是否是第三方应用启动拍照功能

mIsImageCaptureIntent = isImageCaptureIntent();

// 设置UI布局文件

setContentView(R.layout.camera);

if (mIsImageCaptureIntent) {

       // 当第三方其送拍照，需要显示不同的UI，比如取消键盘

       mReviewDoneButton = (Rotatable) findViewById(R.id.btn_done);

       mReviewCancelButton = (Rotatable) findViewById(R.id.btn_cancel);

       findViewById(R.id.btn_cancel).setVisibility(View.VISIBLE);

} else {

       // 反之显示缩略图

       mThumbnailView = (RotateImageView) findViewById(R.id.thumbnail);

       mThumbnailView.enableFilter(false);

       mThumbnailView.setVisibility(View.VISIBLE);

}

// 一个能旋转的dialog.比如相机设置的dialog,这个类实现了旋转的父类

mRotateDialog = new RotateDialogController(this, R.layout.rotate_dialog);

// 设置camera的ID，写道SharedPreference中

mPreferences.setLocalId(this, mCameraId);

// 更新preference

CameraSettings.upgradeLocalPreferences(mPreferences.getLocal());

// 获得相机数

mNumberOfCameras = CameraHolder.instance().getNumberOfCameras();

//  貌似是获得是否是快速拍照

mQuickCapture = getIntent().getBooleanExtra(EXTRA_QUICK_CAPTURE, false);

// 为当前的preview重置曝光值

resetExposureCompensation();

// 隐藏系统导航栏等

Util.enterLightsOutMode(getWindow());

//SurfaceView

SurfaceView preview = (SurfaceView) findViewById(R.id.camera_preview);

SurfaceHolder holder = preview.getHolder();

holder.addCallback(this);

holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

try {

       // 这个join语句就是为了保证openCamera的线程执行完后，当前的线程才开始运行。主要是为了确保camera设备被打开了

        mCameraOpenThread.join();

        // 线程执行完后置为空来让系统回收资源

        mCameraOpenThread = null;

        if (mOpenCameraFail) {

            // 打开camera失败，显示“无法连接到相机”

            Util.showErrorAndFinish(this, R.string.cannot_connect_camera);

            return;

        } else if (mCameraDisabled) {

            // 由于安全政策限制，相机已被停用

            Util.showErrorAndFinish(this, R.string.camera_disabled);

            return;

        }

} catch (InterruptedException ex) {

           // ignore

}

//开启显示的子线程

mCameraPreviewThread.start();

if (mIsImageCaptureIntent) {

    //如果是第三方开启的 ，setupCaptureParams 设置拍照的参数

     setupCaptureParams();

} else {

      //设置ModePicker

      mModePicker = (ModePicker) findViewById(R.id.mode_picker);

      mModePicker.setVisibility(View.VISIBLE);

      mModePicker.setOnModeChangeListener(this);

      mModePicker.setCurrentMode(ModePicker.MODE_CAMERA);

}

mZoomControl = (ZoomControl) findViewById(R.id.zoom_control);

mOnScreenIndicators = (Rotatable) findViewById(R.id.on_screen_indicators);

mLocationManager = new LocationManager(this, this);

//摄像头ID

mBackCameraId = CameraHolder.instance().getBackCameraId();

mFrontCameraId = CameraHolder.instance().getFrontCameraId();

// 在startPreview里面有notify方法

synchronized (mCameraPreviewThread) {

      try {

          mCameraPreviewThread.wait();

       } catch (InterruptedException ex) {

            // ignore

       }

}

// 初始化各种控制按钮

initializeIndicatorControl();

//初始化拍照声音

mCameraSound = new CameraSound();

try {

       //确保显示

       mCameraPreviewThread.join();

} catch (InterruptedException ex) {

        // ignore

}

mCameraPreviewThread = null;

// 确保在holder中有surface

 if (holder.getSurface() == null) {

       Log.d(TAG, "holder.getSurface() == null");

        return;

}

// We need to save the holder for later use, even when the mCameraDevice

// is null. This could happen if onResume() is invoked after this

// function.

mSurfaceHolder = holder;

if (mCameraDevice == null) return;

if (mPausing || isFinishing()) return;

// Set preview display if the surface is being created. Preview was

// already started. Also restart the preview if display rotation has

// changed. Sometimes this happens when the device is held in portrait

// and camera app is opened. Rotation animation takes some time and

// display rotation in onCreate may not be what we want.

if (mCameraState == PREVIEW_STOPPED) {

        startPreview();

        startFaceDetection();

} else {

        if (Util.getDisplayRotation(this) != mDisplayRotation) {

            setDisplayOrientation();

}

        if (holder.isCreating()) {

            // Set preview display if the surface is being created and preview

            // was already started. That means preview display was set to null

            // and we need to set it now.

            setPreviewDisplay(holder);

        }

}

// If first time initialization is not finished, send a message to do

// it later. We want to finish surfaceChanged as soon as possible to let

// user see preview first.

if (!mFirstTimeInitialized) {

       mHandler.sendEmptyMessage(FIRST_TIME_INIT);

} else {

      initializeSecondTime();

 }

/**

     * 初始化，第一次初始化

     *  // Snapshots can only be taken after this is called. It should be called

     *  // once only. We could have done these things in onCreate() but we want to

     *  // make preview screen appear as soon as possible.

     */

    private void initializeFirstTime() {

        if (mFirstTimeInitialized) return;

        // Create orientation listenter. This should be done first because it

        // takes some time to get first orientation.

        mOrientationListener = new MyOrientationEventListener(Camera.this);

        mOrientationListener.enable();

        // Initialize location sevice.

        boolean recordLocation = RecordLocationPreference.get(

                mPreferences, getContentResolver());

        // 初始化屏幕最上方的标志，比如开启了曝光值啊，什么的

        initOnScreenIndicator();

        // 位置服务

        mLocationManager.recordLocation(recordLocation);

        keepMediaProviderInstance();

        // 检查存储空间和初始化储存目录

        checkStorage();

        // Initialize last picture button.

        mContentResolver = getContentResolver();

        if (!mIsImageCaptureIntent) {  // no thumbnail in image capture intent

            // 初始化缩略图

            initThumbnailButton();

        }

        // Initialize shutter button.

        // 初始化拍照按钮并设置监听事件

        mShutterButton = (ShutterButton) findViewById(R.id.shutter_button);

        mShutterButton.setOnShutterButtonListener(this);

        mShutterButton.setVisibility(View.VISIBLE);

        // Initialize focus UI.

        mPreviewFrame = findViewById(R.id.camera_preview);

        mPreviewFrame.setOnTouchListener(this);

        // 聚焦框

        mFocusAreaIndicator = (RotateLayout) findViewById(R.id.focus_indicator_rotate_layout);

        CameraInfo info = CameraHolder.instance().getCameraInfo()[mCameraId];

        boolean mirror = (info.facing == CameraInfo.CAMERA_FACING_FRONT);

        mFocusManager.initialize(mFocusAreaIndicator, mPreviewFrame, mFaceView, this,

                mirror, mDisplayOrientation);

        // 初始化一个图片的保存线程

        mImageSaver = new ImageSaver();

        // 设置屏幕亮度

        Util.initializeScreenBrightness(getWindow(), getContentResolver());

        // 注册SD卡相关的广播，比如拔出存储卡什么的

        installIntentFilter();

        // 初始化缩放UI

        initializeZoom();

        // 更新屏幕上的闪光灯什么的标记

        updateOnScreenIndicators();

        // 开始面部检测

        startFaceDetection();

        // Show the tap to focus toast if this is the first start.

        // 假如是第一次启动，提示用户“触摸对焦”

        if (mFocusAreaSupported &&

                mPreferences.getBoolean(CameraSettings.KEY_CAMERA_FIRST_USE_HINT_SHOWN, true)) {

            // Delay the toast for one second to wait for orientation.

            mHandler.sendEmptyMessageDelayed(SHOW_TAP_TO_FOCUS_TOAST, 1000);

        }

        mFirstTimeInitialized = true;

        addIdleHandler();

    }

/**

     *  // If the activity is paused and resumed, this method will be called in

     *  // onResume.

     */

    private void initializeSecondTime() {

        // Start orientation listener as soon as possible because it takes

        // some time to get first orientation.

        //方向翻转设置enable，其中包括翻转的时候的动画

        mOrientationListener.enable();

        // Start location update if needed.

        boolean recordLocation = RecordLocationPreference.get(

                mPreferences, getContentResolver());

        mLocationManager.recordLocation(recordLocation);

        //设置SD卡广播

        installIntentFilter();

        mImageSaver = new ImageSaver();

        //初始化Zoom

        initializeZoom();

        //mMediaProviderClient=媒体Provider对象

        keepMediaProviderInstance();

        //检查硬盘

        checkStorage();

        //淡出retake和done的Button

        hidePostCaptureAlert();

        if (!mIsImageCaptureIntent) {

            //如果不是第三方开启，则更新缩略图

            updateThumbnailButton();

            mModePicker.setCurrentMode(ModePicker.MODE_CAMERA);

        }

    }

stopPreview();

mSurfaceHolder = null;