除非位置已更改，否则无法获取位置坐标

Question

这是我需要做的。我需要启动我的应用程序并单击一个按钮，我需要显示当前坐标，即纬度和经度。我遵循this 教程并使用以下代码来达到我的目的：

public class MainActivity extends Activity {

    public double latitude;
    public double longitude;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }

        LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        LocationListener locationListener = new MyLocationListener();
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
    }

    @Override
    protected void onStart() {
        super.onStart();
        final TextView latValueLabel = (TextView)findViewById(R.id.latLabel);
        final TextView lonValueLabel = (TextView)findViewById(R.id.lonLabel);
        Button setButton = (Button)findViewById(R.id.set_button);
        setButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub              
                latValueLabel.setText(String.valueOf(latitude));
                lonValueLabel.setText(String.valueOf(longitude));
            }
        });
    }

    private class MyLocationListener implements LocationListener {

        @Override
        public void onLocationChanged(Location location) {
            // TODO Auto-generated method stub
            if(location != null) {
                latitude = location.getLatitude();
                longitude = location.getLongitude();
            }

        }

        @Override
        public void onProviderDisabled(String provider) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onProviderEnabled(String provider) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // TODO Auto-generated method stub

        }

    }

（仅复制粘贴部分代码，请忽略任何未闭合的括号或类似内容。）

它会随着位置的变化不断地获取纬度经度并将其存储到两个double变量latitude和longitude中，当单击setButton时，它会显示最后存储的纬度值。那将是用户的当前位置。现在的问题是，我启动了应用程序，但仍然停留在启动应用程序的确切位置，我单击了设置按钮。但是当时位置并没有改变，所以纬度和经度显示为零，这是双变量的默认值。我需要带着设备四处走走，以便在获得实际坐标之前更改位置。如何在应用启动后立即获得经纬度？

Answer 1

您可以使用getLastKnownLocation(...) 来初始化经度和纬度值，如下所示：

LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);

double longitude = location.getLongitude();
double latitude = location.getLatitude();

Answer 2

这是你的总课。

public class MainActivity extends Activity {

    public double latitude;
    public double longitude;
    private TextView latValueLabel,lonValueLabel ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }

        LocationManager locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        LocationListener locationListener = new MyLocationListener();
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
    }

    @Override
    protected void onStart() {
        super.onStart();
        latValueLabel = (TextView)findViewById(R.id.latLabel);
        lonValueLabel = (TextView)findViewById(R.id.lonLabel);
        Button setButton = (Button)findViewById(R.id.set_button);
        setButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {             
                latValueLabel.setText(String.valueOf(latitude));
                lonValueLabel.setText(String.valueOf(longitude));
            }
        });
    }

    private class MyLocationListener implements LocationListener {

        @Override
        public void onLocationChanged(Location location) {
            if(location != null) {
                latitude = location.getLatitude();
                longitude = location.getLongitude();
                latValueLabel.setText(String.valueOf(latitude));
                lonValueLabel.setText(String.valueOf(longitude));
            }
        }

        @Override
        public void onProviderDisabled(String provider) {

        }

        @Override
        public void onProviderEnabled(String provider) {

        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {

        }
    }
}