Android -- Camera源码简析，启动流程

 com.android.camera.Camera.java，主要的实现Activity，继承于ActivityBase。

ActivityBase

在ActivityBase中执行流程：

onCreate中进行判断是否是平板;

onResume中判断是否锁屏，锁屏&camera不存在时候，mOnResumePending置为true，否则置为false并执行doOnResume;

onWindowFocusChanged中判断是否获取到焦点&mOnResumePending，满足的话执行doOnResume;

onPause中将mOnResumePending置为false;

Camera.java

接下来分析Camera.java，执行流程：

1、onCreate

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// 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;

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2、surfaceCreated

啥都没做

3、surfaceChanged

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// 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[!--empirenews.page--]

// 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();

}

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如果是第一次加载，则执行mHandler.sendEmptyMessage(FIRST_TIME_INIT); 对应处理的是initializeFirstTime();

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/**

* 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();

}

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如果不是，则执行initializeSecondTime();

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/**

* // 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.[!--empirenews.page--]

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);

}

}

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4、surfaceDestroyed

stopPreview();

mSurfaceHolder = null;