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