我正在尝试运行下面的代码，以征询用户使用位置服务的许可。 当我运行下面的程序时，屏幕上不会显示Allow "Location Demo" to access this device's location消息（“ Location Demo”是项目的名称）。
public class MainActivity extends AppCompatActivity {
private LocationManager manager;
private LocationListener listener;
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
manager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener);
}
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
manager = (LocationManager)this.getSystemService(Context.LOCATION_SERVICE);
listener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
Log.i("Location", location.toString());
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
};
// Here, if I change the "!=" to "==", the condition holds
if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
}
}
}
当我将底部的'if'语句从“！=”更改为“ ==”时，上述消息确实出现。因此，我得出的结论是，“ if”中语句的初始值是表明权限实际上是由用户授予的值（甚至在消息启动之前）。 那样行吗？是什么原因造成的？ 希望我要问的清楚 预先谢谢你