0

我正在制作一个需要在继续之前找到用户的 GPS 位置的应用程序。我通过实现 LocationListener 接口来做到这一点。

public void onLocationChanged(Location loc) {
    // TODO Auto-generated method stub
    if(loc!=null){
        loc.getLatitude();
        loc.getLongitude();
        text = "My current location is: " + "Latitude = " + loc.getLatitude() + "Longitude = " + loc.getLongitude();
        Toast.makeText(getApplicationContext(),text, Toast.LENGTH_SHORT).show();
    }
}

但是我在 getApplicationContext() 方法中得到了 NullPointerException。我也尝试了 MyClass.this，但结果相同。当我在 onCreate 中显示吐司时，吐司工作正常。我查找了与此类似的其他问题，但没有一个解决方案有效。我在 onCreate 中使用 setContentView，如下所示：

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

logcat 显示了这一点：

03-14 14:05:48.396: E/AndroidRuntime(604): FATAL EXCEPTION: main
03-14 14:05:48.396: E/AndroidRuntime(604): java.lang.NullPointerException
03-14 14:05:48.396: E/AndroidRuntime(604):  at emergency.app.MyLocationListener.onLocationChanged(MyLocationListener.java:53)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:227)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.location.LocationManager$ListenerTransport.access$000(LocationManager.java:160)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:176)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.os.Looper.loop(Looper.java:137)
03-14 14:05:48.396: E/AndroidRuntime(604):  at android.app.ActivityThread.main(ActivityThread.java:4340)
03-14 14:05:48.396: E/AndroidRuntime(604):  at java.lang.reflect.Method.invokeNative(Native Method)
03-14 14:05:48.396: E/AndroidRuntime(604):  at java.lang.reflect.Method.invoke(Method.java:511)
03-14 14:05:48.396: E/AndroidRuntime(604):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-14 14:05:48.396: E/AndroidRuntime(604):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-14 14:05:48.396: E/AndroidRuntime(604):  at dalvik.system.NativeStart.main(Native Method)

有人能告诉我如何克服这个吗？我是android的初学者，所以我真的需要帮助！

4

3 回答 3

0

使用当前上下文 (=this)而不是应用程序范围的上下文。

Toast.makeText(this,text, Toast.LENGTH_SHORT).show();
于 2013-03-13T13:24:06.123 回答
0

试试下面的代码

Handler handler = new Handler() {
    public void handleMessage(android.os.Message msg) {
        if (msg.what == 0) {
            Toast.makeText(YourActivity.this, (String) msg.obj,
                    Toast.LENGTH_SHORT).show();
        }
    };
};


public void onLocationChanged(Location loc) {
// TODO Auto-generated method stub
    if(loc!=null){
        loc.getLatitude();
        loc.getLongitude();
        text = "My current location is: " + "Latitude = " + loc.getLatitude() + "Longitude = " + loc.getLongitude();

        Message msg = new Message();
        msg.what=0;
        msg.obj= text;
        handler.sendMessage(msg);
    }
}
于 2013-03-13T13:40:02.253 回答
0

下面的代码在我的手机中工作，并在 Toast 中给我定位点。

public class LocationActivity extends Activity implements LocationListener {

Handler handler = new Handler() {
    public void handleMessage(android.os.Message msg) {
        if (msg.what == 0) {
            Toast.makeText(LocationActivity.this, (String) msg.obj,
                    Toast.LENGTH_SHORT).show();
        }
    };
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    LocationManager locationManager = (LocationManager) this
            .getSystemService(Context.LOCATION_SERVICE);
    locationManager.requestLocationUpdates(
            LocationManager.NETWORK_PROVIDER, 0, 0, this);
}

@Override
public void onLocationChanged(Location location) {
    System.out.println("onLocationChanged :");
    if (location != null) {
        location.getLatitude();
        location.getLongitude();
        String text = "My current location is: " + "Latitude = "
                + location.getLatitude() + "Longitude = "
                + location.getLongitude();
        Message msg = new Message();
        msg.what = 0;
        msg.obj = text;
        handler.sendMessage(msg);
    }
}

@Override
public void onProviderDisabled(String provider) {
}

@Override
public void onProviderEnabled(String provider) {
}

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

}

还在清单文件中添加权限。

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
于 2013-03-14T09:49:45.360 回答