autoFocus抛出异常

Question

我什么都试过了，但还是不能解决这个问题。

我在一个应用程序中实现了一个相机功能，除了自动对焦之外，一切都很好。当我调用autoFocus()时，它抛出一个异常，我不明白为什么。我在Desire HD上运行代码。

代码：

@Override
protected void onStart() {
     super.onStart();

     //grab seurface view and callback
     cameraView = (CameraSurfaceView) findViewById(R.id.cameraView);
     try{
        camera = Camera.open();
        cameraView.setCamera(camera);
        //release previous autofocus and assign new one
        camera.cancelAutoFocus();
        camera.autoFocus(new Camera.AutoFocusCallback() {

                public void onAutoFocus(boolean success, Camera camera) {
                // TODO Auto-generated method stub

                }});
    }
    catch (Exception e) {
        //had an issue accessing the camera prompt user
        //TODO create user prompt
        e.printStackTrace();
    }
}

堆栈跟踪：

01-11 16:09:38.456: W/System.err(26546): java.lang.RuntimeException: autoFocus failed
01-11 16:09:38.456: W/System.err(26546):    at android.hardware.Camera.native_autoFocus(Native Method)
01-11 16:09:38.456: W/System.err(26546):    at android.hardware.Camera.autoFocus(Camera.java:680)
01-11 16:09:38.456: W/System.err(26546):    at com.myapp.MyActivity.onStart(BarcodeScannerActivity.java:57)
01-11 16:09:38.466: W/System.err(26546):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1201)
01-11 16:09:38.466: W/System.err(26546):    at android.app.Activity.performStart(Activity.java:3955)
01-11 16:09:38.466: W/System.err(26546):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1845)
01-11 16:09:38.466: W/System.err(26546):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1893)
01-11 16:09:38.466: W/System.err(26546):    at android.app.ActivityThread.access$1500(ActivityThread.java:135)
01-11 16:09:38.466: W/System.err(26546):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1054)
01-11 16:09:38.466: W/System.err(26546):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-11 16:09:38.466: W/System.err(26546):    at android.os.Looper.loop(Looper.java:150)
01-11 16:09:38.476: W/System.err(26546):    at android.app.ActivityThread.main(ActivityThread.java:4385)
01-11 16:09:38.476: W/System.err(26546):    at java.lang.reflect.Method.invokeNative(Native Method)
01-11 16:09:38.476: W/System.err(26546):    at java.lang.reflect.Method.invoke(Method.java:507)
01-11 16:09:38.476: W/System.err(26546):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
01-11 16:09:38.476: W/System.err(26546):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
01-11 16:09:38.476: W/System.err(26546):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

使用SurfaceHolder.Callback -> surfaceCreated了解何时可以启动AutoFocus。如果未创建(持续一段时间)表面持有者，则自动对焦将失败。

Answer 2

您可能需要确保手机支持自动对焦。检查这一点非常容易：

Camera.Parameters p = mCamera.getParameters();
List<String> focusModes = p.getSupportedFocusModes();

if(focusModes != null && focusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO)) {
    //Phone supports autofocus!
}
else {
    //Phone does not support autofocus!
}

Answer 3

我提出了两个对我有效的解决方案。1)正确停止并恢复摄像头。我通过在onPause和onResume上调用这些方法来做到这一点，也是在相机预览的中间，我在应用程序中扫描二维码：

public void stopCamera(){
     mCamera.cancelAutoFocus();
     mCamera.setPreviewCallback(null);
     mCamera.stopPreview();  
     mPreviewing = false;
     }

public void rethrottleCamera(){
        updateViews(); //Updates my Layouts
        mPreviewing = true;
        mCamera.startPreview();
        mCamera.setPreviewCallback(previewCb);  
        mCamera.autoFocus(autoFocusCB); 
        }   

2)非常棘手，但像魔术一样工作！确保在创建预览曲面后调用自动聚焦。为此，运行具有200ms延迟的自动聚焦，以便为创建曲面争取时间。通过在"CameraPreview“对象声明上按ctrl+clic来设置它，例如：

CameraPreview my_camera;

查找"public void surfaceChanged“方法并进行以下更改：

//Add a delay to AUTOFOCUS after mCamera.startpreview();!!:
    mCamera.startPreview();                 
    final Handler handler = new Handler();
    handler.postDelayed(new Runnable() {
        @Override
        public void run() {                    
            mCamera.autoFocus(autoFocusCallback);
            }
    }, 200); //<-200 millisecond delay

    //If you call autofocus right after startPreview, chances are,
    //that the previewSurface will have not been created yet,
    //and autofocus will fail:
    mCamera.startPreview();               //Bad idea!
    mCamera.autoFocus(autoFocusCallback); //Bad idea!

还有很多其他的修复，但这两个可能会挽救你的一天。