java - 从 MainActivity 的 Button Click 中的 Fragment 访问方法

Question

各位，

我正在尝试通过在 MainActivity 中单击按钮向 MapFragment(Fragment) 发送用户当前的纬度和经度。我使用在 MainActivity 中实现的 fragment 的接口(interface)，但是当我尝试从 fragment onButtonClick 访问方法时，我得到一个

at android.app.ActivityThread.main(ActivityThread.java:5221)             at java.lang.reflect.Method.invoke(Native Method)             at java.lang.reflect.Method.invoke(Method.java:372)             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.xtechkid.blah.threadingapplication.MapDemoActivity.setupCurrlocation(com.google.android.gms.maps.model.LatLng)' on a null object reference at com.xtechkid.sudheej.threadingapplication.MainActivity.findLocation(MainActivity.java:67)

我的代码在下面

这是 map fragment

public class MapDemoActivity extends Fragment {
final LatLng MU = new LatLng(40.8874245, 67.0200729);
private GoogleMap mMap; // Might be null if Google Play services APK is not available.
CommInter mCallback;
public interface CommInter {
    public void communicatesWithActivity(double lati,double longi);
}


@Override
public void onAttach(Context context) {
    super.onAttach(context);

    Activity a;

   // if (context instanceof Activity){
        a=(Activity) context;
    //}

    try{
        mCallback = (CommInter) a;
    }catch (ClassCastException e){
        throw new ClassCastException(a.toString());
    }
}
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.activity_main, container, false);

    //setUpMapIfNeeded();

    if (mMap != null) {
        mMap.setMyLocationEnabled(true);
    }

    return view;
}
//This method when called from Main is throwing Exception
public void setupCurrlocation(LatLng MUSEUM) {
    makeText(getContext(), "I am inside the function ", Toast.LENGTH_LONG).show();
    System.out.println("I am inside the function");
    /*CameraPosition cameraPosition = new CameraPosition.Builder()
            .target(MUSEUM)
            .zoom(10)
            .bearing(70)
            .tilt(25)
            .build();
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
*/
    }

}

主要 Activity 的代码

import android.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.content.Intent;
import android.location.LocationManager;
import android.os.Bundle;
import android.provider.Settings;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
import com.google.android.gms.maps.model.LatLng;

public class MainActivity extends AppCompatActivity implements       MapDemoActivity.CommInter  {

private TextView txtLocation;
private String provider;

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

@Override
public void communicatesWithActivity(double lati, double longi) {
    MapDemoActivity mapFrag = (MapDemoActivity)getSupportFragmentManager().findFragmentById(R.id.map);
    final LatLng MUSEU = new LatLng(38.8874245, 77.0200729);
    //final LatLng MUSEU = new LatLng(lati, longi);
    mapFrag.setupCurrlocation(MUSEU);
}

public void findLocation(View v) {
    //final LatLng setLoc =  new LatLng(38.8874245, -77.0200729);
   //// MapDemoActivity fragment;
   // Fragment t = (Fragment)getSupportFragmentManager()findViewById(R.id.map);
   // fragment.setupCurrlocation(v,setLoc);
    txtLocation = (TextView) findViewById(R.id.textViewLocation);
    LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
    boolean isLocEnabled = service.isProviderEnabled(LocationManager.GPS_PROVIDER);
    if (!isLocEnabled) {
        Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
        startActivity(intent);
    }

    GPSTracker gps = new GPSTracker(MainActivity.this);

    // check if GPS enabled
    if(gps.canGetLocation()){

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

        // \n is for new line

        Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
        txtLocation.setText("Lat: " + latitude + "Long: " + longitude);

        //System.out.println(MUS);
        //The PROBLEM IS HERE I DONT KNOW THE FIX 
        communicatesWithActivity(latitude,long);


    }else{
        // can't get location
        // GPS or Network is not enabled
        // Ask user to enable GPS/network in settings
        gps.showSettingsAlert();
    }


    }

}

Answer 1

您没有使用谷歌地图。您需要在调用 setupcurrlocation 的地方进行所有这些导入。

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
// et al...

public void setupCurrlocation(LatLng MUSEUM) {
    GoogleMap googleMap = ((MapFragment) fragmentManager.
                    findFragmentById(R.id.map)).getMap();
    googleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
    Marker marker = googleMap.addMarker(new MarkerOptions().position(latLng).title(null));
    CameraPosition cameraPosition = new CameraPosition.Builder().target(MUSEUM).zoom(10).bearing(70).tilt(25)
                            .build();
    googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

}

基本上，我会在 fragment 所附加的 Activity 中使用此方法。然后您需要管理谷歌地图的可见性。因为它将保留在其他 fragment 之上。
通过控制框架布局的可见性，您可以控制 map 在其框架布局内的可见性。

示例:

// your activity layout here:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    //TO DO/>

    <RelativeLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/myrellayout">

        // ALL THE THINGS IN YOUR ACTIVTY

    </RelativeLayout>

    // THE FRAMELAYOUTS MANAGE YOUR MAP FRAGMENT AND OTHER FRAGMENTS VISIBILITY

    <FrameLayout
        android:id="@+id/firstfrag"
        android:layout_below="@+id/myrellayout"
        android:layout_height="fill_parent"
        android:layout_width="match_parent"
        android:visibility="gone"/>

    <FrameLayout
        android:id="@+id/secondfrag"
        android:layout_below="@+id/myrellayout"
        android:layout_height="fill_parent"
        android:layout_width="match_parent"
        android:visibility="gone"/>

        <fragment
            android:id="@+id/map"
            android:layout_height="match_parent"
            android:layout_width="match_parent"
            android:name="com.google.android.gms.maps.MapFragment"/>
    </FrameLayout>
</RelativeLayout>

https://developers.google.com/maps/documentation/android-api/ https://developers.google.com/maps/documentation/javascript/examples/