Question

I have modified the “CameraTestActivity” so when it scanned the QR code then it will go to next activity.. But every time when I pressed back button to go back “CameraTestActivity”. The app will crash.

I suspect is because onPuase will releaseCamera() so when it come back it cant find the object. If I not releaseCamera then the camera app will locked.

So anyone can teach me how to design the activity flow?

public class CameraTestActivity extends Activity

private Camera mCamera;
private CameraPreview mPreview;
private Handler autoFocusHandler;
private boolean barcodeScanned = false;
private boolean previewing = true;

TextView scanText;
Button scanButton;
ImageScanner scanner;
Context tx;
static Intent anotherActivityIntent;

static {
    System.loadLibrary("iconv");
} 


public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

    autoFocusHandler = new Handler();
    mCamera = getCameraInstance();

    tx = this.getApplicationContext();
    /* Instance barcode scanner */
    scanner = new ImageScanner();
    scanner.setConfig(0, Config.X_DENSITY, 3);
    scanner.setConfig(0, Config.Y_DENSITY, 3);

    mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB);
    FrameLayout preview = (FrameLayout)findViewById(R.id.cameraPreview);
    preview.addView(mPreview);

    scanText = (TextView)findViewById(R.id.scanText);

    scanButton = (Button)findViewById(R.id.ScanButton);

    scanButton.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                if (barcodeScanned) {
                    barcodeScanned = false;
                    scanText.setText("Scanning...");
                    mCamera.setPreviewCallback(previewCb);
                    mCamera.startPreview();
                    previewing = true;
                    mCamera.autoFocus(autoFocusCB);
                }
            }
        });
}

public void onBackPressed() {
    super.onBackPressed();
    releaseCamera();
}

public void onPause() {
    super.onPause();
    releaseCamera();
}

public void onResume() {
    super.onResume();       
}

/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open();
    } catch (Exception e){
    }
    return c;
}

private void releaseCamera() {
    if (mCamera != null) {
        previewing = false;
        mCamera.setPreviewCallback(null);
        mCamera.release();
        mCamera = null;
    }
}

private Runnable doAutoFocus = new Runnable() {
        public void run() {
            if (previewing)
                mCamera.autoFocus(autoFocusCB);
        }
    };

PreviewCallback previewCb = new PreviewCallback() {
        public void onPreviewFrame(byte[] data, Camera camera) {
            Camera.Parameters parameters = camera.getParameters();
            Size size = parameters.getPreviewSize();

            Image barcode = new Image(size.width, size.height, "Y800");
            barcode.setData(data);

            int result = scanner.scanImage(barcode);
            String fileName = "";
            if (result != 0) {
                previewing = false;
                mCamera.setPreviewCallback(null);
                mCamera.stopPreview();

                SymbolSet syms = scanner.getResults();
                for (Symbol sym : syms) {
                    scanText.setText("barcode result " + sym.getData());
                    fileName += sym.getData();
                    barcodeScanned = true;
                }

                anotherActivityIntent = new Intent(tx, TakePhoto.class);
                anotherActivityIntent.putExtra("fileName",fileName +".jpg");                    

                startActivity(anotherActivityIntent);
            }
        }
    };

// Mimic continuous auto-focusing
AutoFocusCallback autoFocusCB = new AutoFocusCallback() {
        public void onAutoFocus(boolean success, Camera camera) {
            autoFocusHandler.postDelayed(doAutoFocus, 1000);
        }
    };

Answer 1

If you release the camera inside the onPause() you have to connect to the camera again in the onResume().

So:

 public void onResume() {
     super.onResume();      
     mCamera = getCameraInstance();
 }

And then you can remove this call from the onCreate