我有一个使用条形码扫描器将数据传递到下一个活动的应用程序。我已设法将数据传递到下一个活动，但当我返回条形码扫描仪时，应用程序崩溃。我认为这是因为它试图再次打开Surfaceview。
返回条形码扫描仪时如何继续使用surfaceview
****条形码扫描仪****
public class BarcodeScannerNew extends AppCompatActivity {
private Camera mCamera;
private CameraPreview mPreview;
private Handler autoFocusHandler;
private Button scanButton;
private ImageScanner scanner;
private boolean barcodeScanned = false;
private boolean previewing = true;
static {
System.loadLibrary("iconv");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.new_barcode_window);
initControls();
}
private void initControls() {
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
autoFocusHandler = new Handler();
mCamera = getCameraInstance();
// Instance barcode scanner
scanner = new ImageScanner();
scanner.setConfig(0, Config.X_DENSITY, 10);
scanner.setConfig(0, Config.Y_DENSITY, 10);
mPreview = new CameraPreview(BarcodeScannerNew.this, mCamera, previewCb,
autoFocusCB);
FrameLayout preview = (FrameLayout) findViewById(R.id.cameraPreview);
preview.addView(mPreview);
scanButton = (Button) findViewById(R.id.ScanButton);
scanButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (barcodeScanned) {
barcodeScanned = false;
mCamera.setPreviewCallback(previewCb);
mCamera.startPreview();
previewing = true;
mCamera.autoFocus(autoFocusCB);
}
}
});
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
releaseCamera();
}
return super.onKeyDown(keyCode, event);
}
/**
* 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);
}
};
Camera.PreviewCallback previewCb = new Camera.PreviewCallback() {
public void onPreviewFrame(byte[] data, Camera camera) {
Camera.Parameters parameters = camera.getParameters();
Camera.Size size = parameters.getPreviewSize();
Image barcode = new Image(size.width, size.height, "Y800");
barcode.setData(data);
int result = scanner.scanImage(barcode);
if (result != 0) {
previewing = false;
mCamera.stopPreview();
mCamera.setPreviewCallback(null);
TextView labelScanResult = (TextView)findViewById(R.id.labelScanResult);
SymbolSet syms = scanner.getResults();
for (Symbol sym : syms) {
Log.i("<<<<<<Asset Code>>>>> ",
"<<<<Bar Code>>> " + sym.getData());
String scanResult = sym.getData().trim();
// shows dialog showAlertDialog(scanResult);
labelScanResult.setText(scanResult);
/* Toast.makeText(BarcodeScanner.this, scanResult,
Toast.LENGTH_SHORT).show();*/
Intent i = new Intent(BarcodeScannerNew.this, BarcodeScanner.class);
i.putExtra("" , labelScanResult.getText().toString());
startActivity(i);
finish();
barcodeScanned = true;
break;
}
}
}
};
// Mimic continuous auto-focusing
Camera.AutoFocusCallback autoFocusCB = new Camera.AutoFocusCallback() {
public void onAutoFocus(boolean success, Camera camera) {
autoFocusHandler.postDelayed(doAutoFocus, 1000);
}
};
private void showAlertDialog(String message) {
new AlertDialog.Builder(this)
.setCancelable(false)
.setMessage(message)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
}
})
.show();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_home, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
if (id == R.id.homebutton){
startActivity(new Intent(this,MainActivity.class));
}
return super.onOptionsItemSelected(item);
}
}
相机活动
package com.example.dsouchon.myapplication;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import java.io.IOException;
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private Camera.PreviewCallback previewCallback;
private Camera.AutoFocusCallback autoFocusCallback;
public CameraPreview(Context context, Camera camera,
Camera.PreviewCallback previewCb,
Camera.AutoFocusCallback autoFocusCb) {
super(context);
mCamera = camera;
previewCallback = previewCb;
autoFocusCallback = autoFocusCb;
/*
* Set camera to continuous focus if supported, otherwise use
* software auto-focus. Only works for API level >=9.
*/
/*
Camera.Parameters parameters = camera.getParameters();
for (String f : parameters.getSupportedFocusModes()) {
if (f == Parameters.FOCUS_MODE_CONTINUOUS_PICTURE) {
mCamera.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
autoFocusCallback = null;
break;
}
}
*/
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
try {
mCamera.setPreviewDisplay(holder);
}
catch (IOException e) {
Log.d("DBG", "Error setting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
/*
* If your preview can change or rotate, take care of those events here.
* Make sure to stop the preview before resizing or reformatting it.
*/
if (mHolder.getSurface() == null) {
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e) {
// ignore: tried to stop a non-existent preview
}
try {
// Hard code camera surface rotation 90 degs to match Activity view in portrait
mCamera.setDisplayOrientation(90);
mCamera.setPreviewDisplay(mHolder);
mCamera.setPreviewCallback(previewCallback);
mCamera.startPreview();
mCamera.autoFocus(autoFocusCallback);
} catch (Exception e) {
Log.d("DBG", "Error starting camera preview: " + e.getMessage());
}
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
}
日志
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.setPreviewDisplay(android.view.SurfaceHolder)' on a null object reference
at com.example.dsouchon.myapplication.CameraPreview.surfaceCreated(CameraPreview.java:56)
at android.view.SurfaceView.updateWindow(SurfaceView.java:607)
at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:184)
at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:921)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2164)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1191)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6642)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:777)
at android.view.Choreographer.doCallbacks(Choreographer.java:590)
at android.view.Choreographer.doFrame(Choreographer.java:560)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:763)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5951)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)