使用YuvImage压缩时出现奇怪的错误

Question

I would like to crop image directly from the Camera Preview using a Rectangle.I get the following error in my LogCat when the following code is used:

skia(24596): onFlyCompress
AndroidRuntime(24596): FATAL EXCEPTION: main
AndroidRuntime(24596): java.lang.NullPointerException
AndroidRuntime(24596):  at com.example.mycameraapp.CameraActivity.getBoundData(CameraActivity.java:417)
AndroidRuntime(24596):  at com.example.mycameraapp.CameraActivity$2.onPreviewFrame(CameraActivity.java:320)
AndroidRuntime(24596):  at android.hardware.Camera$EventHandler.handleMessage(Camera.java:791)
AndroidRuntime(24596):  at android.os.Handler.dispatchMessage(Handler.java:99)
AndroidRuntime(24596):  at android.os.Looper.loop(Looper.java:137)
AndroidRuntime(24596):  at android.app.ActivityThread.main(ActivityThread.java:5103)
AndroidRuntime(24596):  at java.lang.reflect.Method.invokeNative(Native Method)
AndroidRuntime(24596):  at java.lang.reflect.Method.invoke(Method.java:525)
AndroidRuntime(24596):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
AndroidRuntime(24596):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
AndroidRuntime(24596):  at dalvik.system.NativeStart.main(Native Method)

My code generates error in the method getBoundData presumably when I use YuvImage and compressToJpeg methods.The code of the methods is here:

  ByteArrayOutputStream bos;
public byte[] getBoundData(final byte[] data,final Rect rect)
{
    /*int h=mCamera.getParameters().getPictureSize().height;
    int w=mCamera.getParameters().getPictureSize().width;
    int bitsPerPixel=ImageFormat.getBitsPerPixel(mCamera.getParameters().getPictureFormat());
    int bufferSize=w*h*(bitsPerPixel/8);
    byte[] out=new byte[bufferSize];*/
    new Thread()
    {
        public void run()
        {
            final int h=mCamera.getParameters().getPreviewSize().height;
            final int w=mCamera.getParameters().getPreviewSize().width;
            YuvImage yuvImage=new YuvImage(data,ImageFormat.NV21,w,h,null);
            bos=new ByteArrayOutputStream();
            yuvImage.compressToJpeg(rect, 100, bos);
        }
    }.start();  
    //Log.d(TAG,"Bound Array Size: "+bos.size());
    return bos.toByteArray();
}

This method is called within the PreviewCallback like this:

 PreviewCallback mPreviewCallback=new PreviewCallback() {

    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        // TODO Auto-generated method stub
        byte[] boxData=null;
        Rect rect=mBox.getRect();
        if(rect!=null)
            boxData=getBoundData(data,rect);
        else
            boxData=data;
                //file saving code...previously tested.

This is called in using mCamera.setPreviewCallback(mPreviewCallback); within the doSnap method.

What causes this error and how do I rectify it? Also,is this the best way of cropping Image directly from the CameraPreview in Android.

Answer 1

return bos.toByteArray();

You bos is null here. It is only initialized in a background thread later.

If you need to communicate data back from a background thread, use eg a callback interface. AsyncTask makes background thread task handling much simpler BTW.