camera launcher 显示整个过程

1，在camera模块的源码中我们发现DisableCameraReceiver的这样一个类，是继承自BroadcastReceiver一个广播接收器，在AndroidManifest.xml中发现这个reciver的intent-filter为<action android:name="android.intent.action.BOOT_COMPLETED" />，当系统启动之后，该模块就会收到这条系统广播，然后进行相应的处理。

path: packages/apps/Camera/src/com/android/camera/DisableCameraReceiver.java

@Override public void onReceive(Context context, Intent intent) { // Disable camera-related activities if there is no camera. boolean needCameraActivity = FeatureSwitcher.isOnlyCheckBackCamera() ? hasBackCamera() : hasCamera();

if (!needCameraActivity) { Log.i(TAG, "disable all camera activities"); for (int i = 0; i < ACTIVITIES.length; i++) { disableComponent(context, ACTIVITIES[i]); } }

// Disable this receiver so it wont run again. disableComponent(context, "com.android.camera.DisableCameraReceiver"); }

2，可以看到，是通过disableComponent（xx, xx）；来实现对camera应用的隐藏。

private void disableComponent(Context context, String klass) { ComponentName name = new ComponentName(context, klass); PackageManager pm = context.getPackageManager();

// We need the DONT_KILL_APP flag, otherwise we will be killed // immediately because we are in the same app. pm.setComponentEnabledSetting(name, PackageManager.COMPONENT_ENABLED_STATE_DISABLED, PackageManager.DONT_KILL_APP); }

3，是否需要隐藏camera应用，是通过needCameraActivity的值来判断的，如果其值为true，则显示camera应用，否则，就隐藏掉。那么needCameraActivity的值则是通过hasCamera()这个方法读取出来的。

private boolean hasCamera() { int n = FrameworksClassFactory.getNumberOfCameras(); Log.i(TAG, "number of camera: " + n); return (n > 0); }

path: packages/apps/Camera/src/com/android/camera/FrameworksClassFactory.java

public static int getNumberOfCameras() { if (MOCK_CAMERA) { return MockCamera.getNumberOfCameras(); } else { return Camera.getNumberOfCameras(); } }

4，通过阅读代码可以了解到，是通过frameworks/base/core/java/android/hardware/Camera.java中的getNumberOfCameras()方法来获取camera的个数。通过这个函数声明，我们知道，这是一个本地方法，是通过JNI调用来获取的。

public native static int getNumberOfCameras();

5，最后在 frameworks/av/camera/CameraBase.cpp中发现对getNumberOfCameras()函数的实现。

int CameraBase<TCam, TCamTraits>::getNumberOfCameras() { const sp<ICameraService> cs = getCameraService();

if (!cs.get()) { // as required by the public Java APIs return 0; } return cs->getNumberOfCameras(); }

6，cs是CameraService的一个弱引用，找到frameworks/av/services/camera/libcameraservice/CameraService.cpp中的getNumberOfCameras()函数。

int32_t CameraService::getNumberOfCameras() { LOG1("[getNumberOfCameras] NumberOfCameras:%d ", mNumberOfCameras); return mNumberOfCameras; }

7，mNumberOfCameras是一个全局变量，定义在CameraService.h中，其赋值的地方在CameraService.cpp中，

void CameraService::onFirstRef() { LOG1("CameraService::onFirstRef");

BnCameraService::onFirstRef();

if (hw_get_module(CAMERA_HARDWARE_MODULE_ID, (const hw_module_t **)&mModule) < 0) { ALOGE("Could not load camera HAL module"); mNumberOfCameras = 0; } else { ALOGI("Loaded "%s" camera module", mModule->common.name); mNumberOfCameras = mModule->get_number_of_cameras(); if (mNumberOfCameras > MAX_CAMERAS) { ALOGE("Number of cameras(%d) > MAX_CAMERAS(%d).", mNumberOfCameras, MAX_CAMERAS); mNumberOfCameras = MAX_CAMERAS; } //for (int i = 0; i < mNumberOfCameras; i++) { for (int i = 0; i < MAX_CAMERAS; i++) { // workaround for MATV LOG1("setCameraFree(%d)", i); setCameraFree(i); }

if (mModule->common.module_api_version >= CAMERA_MODULE_API_VERSION_2_1) { mModule->set_callbacks(this); }

CameraDeviceFactory::registerService(this); } }