Android(安卓)Camera开发:扫描二维码,周期性循环自动聚焦auto focus挂掉原因分析(preview is not enabled)

问题背景：要让Camera循环聚焦，聚焦完成后进行拍照，在拍照的数据里截取出一定区域的数据。在initCamera里设置聚焦模式：

List<String> allFocus = myParam.getSupportedFocusModes();for(String ff:allFocus){Log.i(tag, ff + "...FOCUS...");}if(allFocus.contains(Camera.Parameters.FLASH_MODE_AUTO)){myParam.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);  Focus_Mode = 1;}else if(allFocus.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO)){myParam.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);  // FOCUS_MODE_CONTINUOUS_PICTURE FOCUS_MODE_AUTOFocus_Mode = 2;}myCamera.setParameters(myParam);

然后有个GetPictureThread进行每隔一段时间聚焦并且拍照：

class GetPictureThread implements Runnable{public void run() {// TODO Auto-generated method stubwhile(!Thread.currentThread().isInterrupted()){if(myCamera != null && isPreview){if(Focus_Mode == 1 && (!isFocusing)){myCamera.autoFocus(mAutoFocusCallback);}else if(Focus_Mode == 2){myCamera.takePicture(myShutterCallback, null, myJpegCallback);}try {Thread.sleep(3000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();Thread.currentThread().interrupt();}}}}}

原来设的GetPictureThread是每隔1200毫秒触发一次，在中兴的Geek手机上一切良好。在华为G700上，总是拍一张就挂，挂的log如下：

12-07 18:05:33.227: D/dalvikvm(13589): threadid=11: exiting12-07 18:05:33.227: W/dalvikvm(13589): threadid=11: thread exiting with uncaught exception (group=0x417669a8)12-07 18:05:33.230: E/AndroidRuntime(13589): FATAL EXCEPTION: Thread-117712-07 18:05:33.230: E/AndroidRuntime(13589): java.lang.RuntimeException: autoFocus failed12-07 18:05:33.230: E/AndroidRuntime(13589): at android.hardware.Camera.native_autoFocus(Native Method)12-07 18:05:33.230: E/AndroidRuntime(13589): at android.hardware.Camera.autoFocus(Camera.java:1120)12-07 18:05:33.230: E/AndroidRuntime(13589): at org.yanzi.rectphoto_wuzhou.RectPhoto$GetPictureThread.run(RectPhoto.java:428)12-07 18:05:33.230: E/AndroidRuntime(13589): at java.lang.Thread.run(Thread.java:838)12-07 18:05:33.240: I/Camera(13589): handleMessage: 2

反正就是auto focus出问题了，单看这里的log看不出所以然来。话说2000元买的G'700还是支持自动聚焦的吧。截取所有的log又看了次，搜索关键字：autofocus，得到以下信息：

  F:\1.log (12 hits)Line 12829: 12-08 10:14:19.477 D/CameraClient(  142): autoFocus (pid 10314)Line 12831: 12-08 10:14:19.477 D/MtkCam/CamDevice(  142): (599)(Default:0)[CamDevice::autoFocus] +Line 12834: 12-08 10:14:19.477 D/MtkCam/CamAdapter(  142): (599)(Default)[autoFocus] +Line 12861: 12-08 10:14:19.477 D/aaa_hal (  142): [autoFocus()]Line 12877: 12-08 10:14:19.477 D/MtkCam/CamAdapter(  142): (599)(Default)[autoFocus] -Line 20489: 12-08 10:14:20.677 D/CameraClient(  142): autoFocus (pid 10314)Line 20491: 12-08 10:14:20.677 D/MtkCam/CamDevice(  142): (142)(Default:0)[CamDevice::autoFocus] +Line 20503: 12-08 10:14:20.678 E/MtkCam/CamDevice(  142): (142)(Default:0)[CamDevice::autoFocus] preview is not enabled (autoFocus){#552:mediatek/hardware/camera/device/CamDevice/CamDevice.cpp}Line 20503: 12-08 10:14:20.678 E/MtkCam/CamDevice(  142): (142)(Default:0)[CamDevice::autoFocus] preview is not enabled (autoFocus){#552:mediatek/hardware/camera/device/CamDevice/CamDevice.cpp}Line 20512: 12-08 10:14:20.679 E/AndroidRuntime(10314): java.lang.RuntimeException: autoFocus failedLine 20514: 12-08 10:14:20.679 E/AndroidRuntime(10314): at android.hardware.Camera.native_autoFocus(Native Method)Line 20516: 12-08 10:14:20.679 E/AndroidRuntime(10314): at android.hardware.Camera.autoFocus(Camera.java:1120)

可以看到，上面提到preview is not enabled，竟然说preview没有开启。可我明明preview已经开启了，而且我在扫描线程里设置了判断if(myCamera != null && isPreview)。参考国外这位大大的帖子http://www.hitziger.net/blog/android-camera-autofocus-failed/上面提到auto focus失败原因是surfaceholder还没有被创建，换句话camera还没有开启预览就进行自动聚焦了。但其实我的扫描线程启动已经加了延迟，确保camera预览已经开启，姑且信了吧。把线程开启的地方加到了surfacechanged，因为我的initcamera是在surfacechanged里面，initcamera的最后就是startPreview。但依然出错。我加了个延迟在surfacechanged依旧报错。后来参考又一个人的帖子，在activity的onResume方法里进行mySurfaceHolder.addCallback(this);确保surfaceview已经创建了再添加回调。这样干确实严谨一点，但依旧报错。事实上这样做不是必须的，因为我把GetPictureThread去掉之后，一切ok。我加个button，拍照的时候自动聚焦，如果聚焦成功再触发takePicture也是ok的。

问题出在哪呢？最后才恍然大悟，问题在拍照的jpegCallback上，代码如下：

PictureCallback myJpegCallback = new PictureCallback() {public void onPictureTaken(byte[] data, Camera camera) {// TODO Auto-generated method stubLog.i(tag, "myJpegCallback:onPictureTaken...");long t1 = System.currentTimeMillis();if(null != data){mBitmap = BitmapFactory.decodeByteArray(data, 0, data.length);myCamera.stopPreview();isPreview = false;}Matrix matrix = new Matrix();matrix.postRotate((float)90.0);Bitmap rotaBitmap = Bitmap.createBitmap(mBitmap, 0, 0, mBitmap.getWidth(), mBitmap.getHeight(), matrix, false);//Bitmap sizeBitmap = Bitmap.createScaledBitmap(rotaBitmap, 540, 800, true);Bitmap rectBitmap = Bitmap.createBitmap(rotaBitmap, square.left, square.top, square.width(), square.height());if(null != rectBitmap){saveThread.setSaveBitmap(rectBitmap);}//ImageUtil.saveJpeg(rotaBitmap);myCamera.startPreview();isPreview = true;long t2 = System.currentTimeMillis();Log.i(tag, "本次保存耗时：" + (t2 - t1) + "毫秒");}};

注意在拍照时，camera首先停止预览保存完照片后再次开启预览。尽管我加了isPreview这个标志，但这个标志位是不起啥作用的。推测，stoppreviw和startpreview的时候，camera在底层是异步处理的。也就是说程序执行到startpreview，isPreview为真了，但这时camera还没有完全开启预览，而扫描线程再次触发auto focus就会报上面的错误。后来我对这个myJpegCallback测了下时间，完全同样的代码，在geek手机上是900多毫秒左右，在G700上是1800毫秒左右，将近2秒了，所以扫描周期一定得大于这个时间。后来将扫描周期设为3秒，两个手机都ok了。但G700上偶发的也还是会报错，这是因为内存占用太多，手机速度变慢，myJpegCallback回调的周期超过了3秒，重启下手机就好了。在AutoFocusCallback里设置标志isFocusing也是必须的。

final AutoFocusCallback mAutoFocusCallback = new AutoFocusCallback() {public void onAutoFocus(boolean success, Camera camera) {// TODO Auto-generated method stubisFocusing = true;if(success){Log.i(tag, "聚焦成功...");myCamera.takePicture(myShutterCallback, null, myJpegCallback);}else{Log.i(tag, "聚焦失败...");}isFocusing = false;}};

看来，要玩Camera还是得整个高端点的手机啊！！！

参考http://stackoverflow.com/questions/5878042/android-camera-autofocus-on-demand自从API9，就有了连续聚焦。参考官方对聚焦模式的说明，http://developer.android.com/reference/android/hardware/Camera.Parameters.html#FOCUS_MODE_CONTINUOUS_VIDEO聚焦最强的是FOCUS_MODE_CONTINUOUS_PICTURE它是和AutoFocus兼容的，其次是

FOCUS_MODE_CONTINUOUS_VIDEO，聚焦强度弱于CONTINUOUS_PICTURE. 所以如果能满足需要的话，FOCUS_MODE_CONTINUOUS_VIDEO 就ok了！有些资料不建议周期性auto focus，但看今天的扫描二维码貌似都是用的auto focus模式，而不是连续聚焦，所以可以肯定，在这种模式下，获得数据是从预览帧里截取的，而不是拍照。因为拍照在普通手机上一定得停预览然后开预览，这个花费时间太大了！如果是为了高更分辨率，只能拍照的话一定要控制好扫描周期。

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