我读了很多关于 onActivityResult的问题，但似乎没有一个描述的问题适用于我的情况，比如在 startActivityForResult 中放置一个负的 requestCode 或其他问题。
我正在我的 Activity 中使用相机，并将其预览流传输到 SurfaceView。
拍照后，关闭相机释放其资源，调用 setResult(RESULT_OK, DataIntent)，希望能够在父级中触发 onActivityResult。
但是它没有触发。如果我在子 Activity 的 onCreate 中设置结果并在 onCreate 中完成子 Activity，则结果不会传递给 onActivityResult。
为什么可能会导致 onActivityResult 没有被触发呢？
下面是一些我正在做的事情的源代码以便理解...
public class MainActivity extends Activity {
Button mButtonScan;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mButtonScan = (Button)findViewById(R.id.main_btn_scan);
}
/**
* OnClick Event called from main.xml
* @param v View that called that onClickEvent
*/
public void btnCaptureClick(View v) {
Intent intent = new Intent(this, CaptureActivity.class);
startActivityForResult(intent, Constants.REQUEST_CODE_CAPTURE);
}
/**
* callback for this Activity. Called when an Activity which was started by
* this.startActivityForResult(intent, requestCode) sets its result and calls finish()
*/
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
String foo = "foo";
switch (requestCode) {
case Constants.REQUEST_CODE_CAPTURE:
switch (resultCode) {
case RESULT_FIRST_USER:
Toast.makeText(this, data.getStringExtra(Config.SCAN_RESULT_TEXT), Toast.LENGTH_LONG).show();
break;
case RESULT_CANCELED:
break;
default:
break;
}
break;
default:
super.onActivityResult(requestCode, resultCode, data);
break;
}
}
}
public class CaptureActivity extends Activity implements ActivityCallback, SurfaceHolder.Callback, PreviewCallback {
private Preview mPreview;
private Camera mCam;
private SurfaceHolder mHolder;
private Size size;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.capture);
mPreview = (Preview)findViewById(R.id.capture_preview);
}
@Override
public void onValidDecodeResult(Result rawResult, Bitmap barcode) {
Intent intent = new Intent();
if (rawResult != null && barcode != null) {
intent.putExtra(Config.SCAN_RESULT_TEXT, rawResult.getText());
intent.putExtra(Config.SCAN_RESULT_FORMAT, rawResult.getBarcodeFormat().getName());
intent.putExtra(Config.SCAN_RESULT_BMP, barcode);
} else {
intent.putExtra(Config.SCAN_RESULT_TEXT, "foo");
intent.putExtra(Config.SCAN_RESULT_FORMAT, "bar");
intent.putExtra(Config.SCAN_RESULT_BMP, "barcode");
}
mPreview = null;
setResult(Activity.RESULT_FIRST_USER, intent);
finish();
}
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
MultiFormatReader reader = new MultiFormatReader();
PlanarYUVLuminanceSource source = new PlanarYUVLuminanceSource(data, size.width, size.height, 160, 60, 480, 360);
GlobalHistogramBinarizer binarizer = new GlobalHistogramBinarizer(source);
BinaryBitmap bb = new BinaryBitmap(binarizer);
Result result = null;
try {
result = reader.decode(bb);
} catch (NotFoundException e) {
//do NOTHING cause e == null
} catch (Exception e){
e.printStackTrace();
} finally {
reader.reset();
}
if (result != null) {
mCam.stopPreview();
releaseCameraResources();
onValidDecodeResult(result, source.renderCroppedGreyscaleBitmap());
} else {
camera.setOneShotPreviewCallback(this);
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
try {
mCam = Camera.open();
mCam.setPreviewDisplay(mPreview.getHolder());
} catch (IOException e) {
releaseCameraResources();
e.printStackTrace();
}
}
private void releaseCameraResources() {
mCam.release();
mCam = null;
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
//begin Preview
Camera.Parameters parameters = mCam.getParameters();
List<Size> sizes = parameters.getSupportedPreviewSizes();
size = getOptimalPreviewSize(sizes, width, height);
parameters.setPreviewSize(size.width, size.height);
mCam.setParameters(parameters);
mCam.startPreview();
mCam.setOneShotPreviewCallback(this);
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
if (mCam != null) {
mCam.stopPreview();
releaseCameraResources();
}
}
private Size getOptimalPreviewSize(List<Size> sizes, int width, int height) {
final double ASPECT_TOLERANCE = 0.05;
double targetRatio = (double) width / height;
if (sizes == null) return null;
Size optimalSize = null;
double minDiff = Double.MAX_VALUE;
int targetHeight = height;
for (Size size: sizes) {
double ratio = (double) size.width / size.height;
if(Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) {
continue;
}
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
if (optimalSize == null) {
//cannot find matching aspect-ratio
minDiff = Double.MAX_VALUE;
for (Size size : sizes) {
if (Math.abs(size.height - targetHeight) < minDiff) {
optimalSize = size;
minDiff = Math.abs(size.height - targetHeight);
}
}
}
return optimalSize;
}
}