Question

我目前修改了“谷歌地图视图”代码（如下所示），但是当地图加载并且您点击地图上的项目时，它会返回错误。

我认为这与mContext的null值有关，但我不确定，如果有人能帮我解决这个问题，我会非常感激：

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

我的地图课程：

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);
    }

    }

我的HelloItemizedOverlay类：

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

您在主类中缺少上下文。

添加：

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

而不是：

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable);

Answer 2

我还发现当您点按标记时，HelloGoogleMaps教程代码失败了。

如果您传递this（来自扩展MapActivity的实例），则会显示对话框。

  HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, this);

需要构造函数：

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

Answer 3

更改两个地方：

1

HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(drawable, this);

2

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

Answer 4

你可以传递这样的上下文，这里是伪代码：

  HelloItemizedOverlay itemizedoverlay = new HelloItemizedOverlay(this,drawable);

当使用onTap（）时，Android Google Map视图会返回错误 - 应该显示Alertdialog

4 个答案: