相机在不需要的活动中启动

Question

我的应用程序中有一个二维码扫描仪，当我的AlertDialog显示时，相机会停止，但当我转到另一个活动时，相机就会重新启动，即使应用程序不在前台，相机也会在后台运行。我有stopCamera((和stopCameraPreview()，但只要应用程序打开(前台和后台(，它就会重新启动并保持打开状态这是活动的代码：

public class MainActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler {
private static final int REQUEST_CAMERA = 1;
private ZXingScannerView scannerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
scannerView = new ZXingScannerView(this);
setContentView(scannerView);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (checkPermission()) {
Toast.makeText(MainActivity.this, "Scanner Active", Toast.LENGTH_LONG).show();
} else {
requestPermission();
}
}
}
private boolean checkPermission() {
return (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED);
}
private void requestPermission() {
ActivityCompat.requestPermissions(this, new String[]{CAMERA}, REQUEST_CAMERA);
}

public void onRequestPermissionsResult(int requestCode, String[] permission, int[] grantResults) {
switch (requestCode) {
case REQUEST_CAMERA:
if (grantResults.length > 0) {
boolean cameraAccepted = grantResults[0] == PackageManager.PERMISSION_GRANTED;
if (cameraAccepted) {
Toast.makeText(MainActivity.this, "Permission Granted!", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(MainActivity.this, "Permission Denied", Toast.LENGTH_LONG).show();
}
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (shouldShowRequestPermissionRationale(CAMERA)) {
displayAlertMessage("You need to allow access for both permsisions",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {

requestPermissions(new String[]{CAMERA}, REQUEST_CAMERA);
}
}
});
return;
}
}
}
break;
}
}
@Override
public void onResume() {
super.onResume();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (checkPermission()) {
if (scannerView == null) {
scannerView = new ZXingScannerView(this);
setContentView(scannerView);
}
scannerView.setResultHandler(this);
scannerView.startCamera();
} else {
requestPermission();
}
}
}
@Override
public void onDestroy() {
super.onDestroy();
scannerView.stopCamera();
scannerView.stopCameraPreview();
}
public void displayAlertMessage(String message, DialogInterface.OnClickListener listener) {
new AlertDialog.Builder(MainActivity.this)
.setMessage(message)
.setPositiveButton("OK", listener)
.setNegativeButton("Cancel", null)
.create()
.show();
}
String[] a = {"ABCD", "PQR"};
String scanned = "";
@Override
public void handleResult(Result result) {
final String scanResult = result.getText();
for (int i = 0; i < 2; i++) {
if (scanResult.equals(a[i])) {
scanned = a[i];
scannerView.stopCamera();
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("QR Scan");
builder.setMessage("Machine Identified!");
builder.setPositiveButton("Continue", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
Intent intent1 = new Intent(MainActivity.this, buttons.class);
startActivity(intent1);
scannerView.stopCameraPreview();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
scannerView.resumeCameraPreview(MainActivity.this);
}
});
builder.show();
break;
} else {
Toast.makeText(this, "ERROR: Unrecognized QR Code", Toast.LENGTH_LONG).show();
scannerView.resumeCameraPreview(MainActivity.this);
}
}
}
}

Answer 1

"即使应用程序不在前台也保持在后台运行"-这是由于"活动"生命周期。请注意，onDestroy()是class Activity的最后一个方法，它被调用，并且只有当活动确实被破坏时才被调用。

它的意思是：当你移动到后台时，不会调用onDestroy()。活动仍然有效，正在等待恢复。您的活动仍然存在，并且应该存在。请使用名为onPause()的onDestroy()方法。如果活动被终止，您将达到此方法，并且在适当的时候它将返回到onResume()。

只需将onDestroy()改写为：

@Override
public void onPause() {
super.onPause();
scannerView.stopCamera();
scannerView.stopCameraPreview();
}