如果活动停止并再次启动，请求启用GPS两次

Question

我有一个活动，通过显示一个带有OK和CANCEL按钮的对话框，请求用户在onStart()中启用GPS。但是，如果用户在与对话框交互之前按下主页按钮，然后再次启动应用程序，则会在旧对话框的顶部出现一个新对话框，因此用户会看到两个对话框一个接一个。如何取消活动的onStop方法中的旧对话框？

这是我代码的相关部分：

protected void onStart() {
super.onStart();
enableGPS();
}
private void enableGPS() {                                      //GPS ENABLE RELATED METHOD
LocationSettingsRequest.Builder builder = new LocationSettingsRequest.Builder()
.addLocationRequest(mLocationRequest);
builder.setAlwaysShow(true);
PendingResult<LocationSettingsResult> result = LocationServices.SettingsApi
.checkLocationSettings(mGoogleApiClient, builder.build());
result.setResultCallback(new ResultCallback<LocationSettingsResult>() {
@Override
public void onResult(LocationSettingsResult result) {
final Status status = result.getStatus();
final LocationSettingsStates state = result
.getLocationSettingsStates();
switch (status.getStatusCode()) {
case LocationSettingsStatusCodes.SUCCESS:                           //GPS ALREDY TURNED ON
if (locationServiceConnected) {
if (ActivityCompat.checkSelfPermission(enableGPSActivity.this, android.Manifest.permission.ACCESS_FINE_LOCATION)== PackageManager.PERMISSION_GRANTED) {
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, enableGPSActivity.this);
}
}
else {
redirectStatus.setText("ERROR: Not able to connect to Location Service");
btnRetry.setVisibility(View.VISIBLE);
}
break;
case LocationSettingsStatusCodes.RESOLUTION_REQUIRED:               //GPS NOT ALREDY TURNED ON, SHOW TURN ON DIALOG
try {
status.startResolutionForResult(enableGPSActivity.this, REQUEST_CHECK_SETTINGS); //CREATING DIALOG FOR GPS TURN ON
} catch (IntentSender.SendIntentException e) {
}
break;
case LocationSettingsStatusCodes.SETTINGS_CHANGE_UNAVAILABLE:       //GPS CANNOT BE TURNED ON
redirectStatus.setText("Permission Available, not able to enable GPS");
btnRetry.setVisibility(View.VISIBLE);
break;
}
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {             //GPS ENABLE RELATED METHOD, DIALOG FOR GPS TURN ON
if (requestCode == REQUEST_CHECK_SETTINGS) {
if (resultCode == Activity.RESULT_OK) {                 // GPS TURN ON ACCEPTED
if (locationServiceConnected) {
if (ActivityCompat.checkSelfPermission(enableGPSActivity.this, android.Manifest.permission.ACCESS_FINE_LOCATION)== PackageManager.PERMISSION_GRANTED) {
redirectStatus.setText("Please Wait. Fetching Your Current Location");
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, enableGPSActivity.this);
}
}
}
if (resultCode == Activity.RESULT_CANCELED) {               //GPS TURN ON REJECTED
redirectStatus.setText("Permission Available, GPS Off");
btnRetry.setVisibility(View.VISIBLE);
}
}
}

}

Answer 1

将enableGPS();调用为onCreate()而不是onStart()
因为

根据Activity-的生命周期，当用户按下主页按钮时，当前活动将通过调用-onPause()和onStop()方法进入后台从Stack恢复活动时，将通过调用onRestart()、onStart()和onResume()来恢复Activity。

Answer 2

//  declares variables name 
private AlertDialog gpsAlertDialog;
private boolean  isGpsDialogShowing = false;
private LocationManager manager;

// check gps enable or not if enable than remove dialog else show gps enable dialog in onResume method

protected void onResume() 
{          
if (!manager.isProviderEnabled(LocationManager.GPS_PROVIDER)&&!manager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) {
ShowGpsDialog();
} else {
removeGpsDialog();
}

}

//   remove dialog on destroy activity 
@Override
protected void onDestroy() {
super.onDestroy();
removeGpsDialog();
}

//   method for show dialog for gps enable    

private void ShowGpsDialog() {
isGpsDialogShowing = true;
AlertDialog.Builder gpsBuilder = new AlertDialog.Builder(
MainMenuDrawerActivity.this);
gpsBuilder.setCancelable(false);
gpsBuilder
.setTitle(getString(R.string.dialog_no_gps))
.setMessage(getString(R.string.dialog_no_gps_messgae))
.setPositiveButton(getString(R.string.dialog_enable_gps),
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
// continue with delete
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent);
removeGpsDialog();
}
})
.setNegativeButton(getString(R.string.dialog_exit),
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
// do nothing
removeGpsDialog();
finish();
}
});
gpsAlertDialog = gpsBuilder.create();
gpsAlertDialog.show();
}

//  method for remove gps dialog 

private void removeGpsDialog() {
if (gpsAlertDialog != null && gpsAlertDialog.isShowing()) {
gpsAlertDialog.dismiss();
isGpsDialogShowing = false;
gpsAlertDialog = null;
}
}