Google map display Google Google returns an error when using onTap () - it is assumed that Alertdialog will be displayed

Question

Currently, I have changed the "Google Map View" code (see below), but when the map loads and you click on an item on the map, it returns an error.

I believe this has something to do with the null value for mContext, but I'm not sure I would really appreciate it if anyone could help me with this:

protected boolean onTap(int index) {
OverlayItem item = mOverlays.get(index);
Context mContext = null;
AlertDialog.Builder dialog = new AlertDialog.Builder(mContext);

My card class:

package testing.map;

import java.util.List;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapView;
import com.google.android.maps.Overlay;
import com.google.android.maps.OverlayItem;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Bundle;

public class Mapview extends MapActivity {
    /** Called when the activity is first created. */

protected boolean isRouteDisplayed(){
    return false;
}
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mapview);

        MapView mapView = (MapView) findViewById(R.id.mapview);
        mapView.setBuiltInZoomControls(true);

        List<Overlay> mapOverlays = mapView.getOverlays();
        Drawable drawable = this.getResources().getDrawable(R.drawable.jd_sports_logo);
        HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable);

        //Declared longitude/latitude as doubles as GeoPoint only uses 'int' - converted to microdegrees
        double latitude = 51.545538;
        double longitude = -0.477247;
        GeoPoint point = new GeoPoint((int)(latitude * 1e6), (int)(longitude * 1e6));

        OverlayItem overlayitem = new OverlayItem(point, "Hola, Mundo!", "I'm in Mexico City!");

        itemizedoverlay.addOverlay(overlayitem);
        mapOverlays.add(itemizedoverlay);
    }

    }

My HelloItemizedOverlay class:

package testing.map;

import java.util.ArrayList;
import android.graphics.drawable.Drawable;
import android.app.AlertDialog;
import android.content.Context;
import com.google.android.maps.ItemizedOverlay;
import com.google.android.maps.OverlayItem;

public class HelloItemizedOverlay extends ItemizedOverlay {

    private ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>();

    public HelloItemizedOverlay(Drawable defaultMarker) {
        super(boundCenterBottom(defaultMarker));

    }
    public void addOverlay(OverlayItem overlay) {

        mOverlays.add(overlay);
        populate();
    }
    public HelloItemizedOverlay(Drawable defaultMarker, Context context) {
          super(defaultMarker);
          Context mContext = context;
        }

    @Override
    protected OverlayItem createItem(int i) {
        // TODO Auto-generated method stub
        return mOverlays.get(i);
    }

    @Override
    public int size() {
        // TODO Auto-generated method stub
        return mOverlays.size();
    }

    @Override
    protected boolean onTap(int index) {
      OverlayItem item = mOverlays.get(index);
      Context mContext = null;
      AlertDialog.Builder dialog = new AlertDialog.Builder(mContext);
      dialog.setTitle(item.getTitle());
      dialog.setMessage(item.getSnippet());
      dialog.show();
      return true;
    }

}

Answer 1

There is no context in the main class.

Add this:

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, mContext);
where mContext = this;

instead of this:

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable);

Answer 2

I also found that the HelloGoogleMapstutorial code failed with npe when the marker was clicked.

this ( , MapActivity), .

  HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, this);

:

public HelloItemizedOverlay(Drawable defaultMarker, Context context) {
          super(defaultMarker);
          mContext = context;
    }

Answer 3

Change two places:

1.

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, this);

2.

public HelloItemizedOverlay(Drawable defaultMarker, Context context) {
    super(boundCenterBottom(defaultMarker));
    mContext = context;
}

Answer 4

you can pass such a context, here is the pseudo code:

  HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(this,drawable);