Question

我想通过点击按钮在tvLatitude和tvLongitude（TextView＆＃39; s）中显示纬度和经度。它不适用于我目前拥有的代码，您可以看到以下代码。问题是当控件到达字符串latitude = Double.toString(loc.getLatitude());时，程序停止运行。有谁可以告诉我为什么loc.getLatitude和loc.getLongitude没有回复？

package mk.bukhari.loctrack;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Build;

public class MainActivity extends ActionBarActivity implements LocationListener {

    TextView tvLat, tvLon;
    Button btnLoc;

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
            tvLat = (TextView) findViewById(R.id.tvLatitude);
            tvLon = (TextView) findViewById(R.id.tvLongitude);
            btnLoc = (Button) findViewById(R.id.btnLocation);

            final LocationManager locman = (LocationManager)
            getSystemService(LOCATION_SERVICE);
            locman.requestLocationUpdates("gps", 0, 0, this);

            btnLoc.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    Log.d("LocTrack", "Button Clicked");
                    Location loc = locman.getLastKnownLocation("gps");
                    onLocationChanged(loc);
                }
            });         
        }
    }
}

    @Override
    public void onLocationChanged(Location loc) {
        Log.d("LocTrack", "Entering onLacationChanged");
        String latitude = Double.toString(loc.getLatitude());
        String longitude = Double.toString(loc.getLongitude());
        Log.d("LocTrack", "Setting txt in tv");
        tvLat.setText(latitude);
        tvLon.setText(longitude);
    }

    @Override
    public void onProviderDisabled(String arg0) {}

    @Override
    public void onProviderEnabled(String arg0) {}

    @Override
    public void onStatusChanged(String arg0, int arg1, Bundle arg2) {}
}

Answer 1

好的，似乎您的位置返回null，请尝试以这种方式更改代码：

@Override
public void onLocationChanged(Location loc) {
    Log.d("LocTrack", "Entering onLacationChanged");

    if(loc != null) { //Add this validation
        String latitude = Double.toString(loc.getLatitude());
        String longitude = Double.toString(loc.getLongitude());
        Log.d("LocTrack", "Setting txt in tv");
        tvLat.setText(latitude);
        tvLon.setText(longitude);
    } else    //If loc is null then inform the user
        Toast.makeText(this, "Unable to find your location, try again", Toast.LENGTH_SHORT).show();
}

Answer 2

好像你使用了错误的提供商。

尝试拨打

locman.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0 , 0, this);

然后在onClick(View v)

中

Location loc = locman.getLastKnownLocation(LocationManager.GPS_PROVIDER);

onLocationChanged（）从未在Android中调用过

2 个答案: