Question

我正在为学校开发一个Android项目。此活动应该获取GPS位置，并能够保存它。然后，用户稍后可以返回应用程序并从当前位置获取到该位置的路线。

对于Android开发者来说还是新手，以下内容仍在进行中。我需要在退出应用程序后保存pinLat和pinLong，以便在应用程序再次打开时可用。

以下是当前的活动：

public class LocationActivity extends Activity implements LocationListener{

// declare variables
float locLat = 0;
float locLong = 0;
float pinLat = 0;
float pinLong = 0;

TextView txtLat;
TextView txtLong;
TextView txtPinLat;
TextView txtPinLong;
LocationManager locationManager;
LocationListener locationListener;
Location location;

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

    // get a handle on the text views
    txtLat = (TextView) findViewById(R.id.txtLat);
    txtLong = (TextView) findViewById(R.id.txtLong);
    txtPinLat = (TextView) findViewById(R.id.txtPinLat);
    txtPinLong = (TextView) findViewById(R.id.txtPinLong);

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

    //Why cant I instantiate the LocationListener?
    locationListener = new LocationListener();
}

public void onLocationChanged(Location location) {
    //if it finds the location
    if (location != null){
    // save the values to float variables
    locLat = (float) location.getLatitude();
    locLong = (float) location.getLongitude();
    // set the text views to the lat and long values
    txtLat.setText(String.valueOf(locLat));
    txtLong.setText(String.valueOf(locLong));
    }
}
//save the current location to be a pin for the map
public void pinLocation(View v) throws IOException {
    // when the button is pressed, save the current location lat and long
    pinLat = locLat;
    pinLong = locLong;

    // set the text views to the lat and long values
    txtPinLat.setText(String.valueOf(pinLat));
    txtPinLong.setText(String.valueOf(pinLong));
}

//launch google maps to navigate to the pin
public void navigate(View v) {
    //Toast.makeText(getApplicationContext(), "Navigate Called!", Toast.LENGTH_LONG).show();
    //build the google maps URL
    String uri = ("geo:"+ pinLat + "," + pinLong);
    //add the lat and long
    String query = pinLat + "," + pinLong;
    //encode the URI
    String encodedQuery = Uri.encode(query);
    //continue building the uri
    uri += "?q=" + encodedQuery;
    //start the intent with the Uri
    Intent navigate = new Intent(Intent.ACTION_VIEW, Uri.parse(uri));
    //start the activity
    startActivity(navigate);
}

//when the app resumes, turn on the GPS locations
public void onResume(){
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,
            5,5, locationListener);
    super.onResume();
}

//on pause, stop the GPS
@Override
public void onPause() {
    locationManager.removeUpdates(locationListener);
    super.onPause();
}


//GENERATED CODE. Need to alert if disabled etc

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

}

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

}

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

}

在onCreate方法中，我在locationListener = new LocationListener（）上得到“无法实例化类型LocationListener”错误;线。我见过其他人在例子中使用了这一行。我错过了什么？

我的AndroidManifest中有权限，布局不应该导致任何问题..

谢谢！

Answer 1

由于您已经implements LocationListener您的活动已经是LocationListener，因此您不必创建新的LocationListener。

删除LocationListener locationListener;

周围的所有实例化

在onResume方法上尝试将请求更新行更改为：

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

onLocationChanged应该触发，你可以从中获取位置。

Answer 2

这更像是一般的Java问题。 LocationListener不是Java类，它是一个接口。简单来说，这意味着没有方法的实现（即onLocationChanged，onProviderEnabled等）。这意味着你必须定义调用这些方法时会发生什么。

如果您熟悉处理Button点击事件，那么您已经知道如何使用匿名内部类编写实现。（AIC就像实现界面＆＃39;即时＃。）。

  LocationListener listener  = new LocationListener() {
      @Override
      public void onLocationChanged(Location location) {
                //TODO -- Barney says what should happen 
                // when the framework invokes onLocationChanged
      }

      //TODO -- Barney implements the other three interface methods

  )}; //Close AIC declaration, implementation and terminate line.

无法实例化类型LocationListener

2 个答案: