试图启动谷歌地图崩溃我的应用程序

Question

在我的Android应用程序，我只是想在用户点击按钮时显示在地图上的位置。但是，当我点击按钮的android模拟器崩溃。

下面是按钮的代码：

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

    Button btn = (Button) findViewById(R.id.btn_map); 
    btn.setOnClickListener(new View.OnClickListener() 
    { 
     public void onClick(View v) 
     { 
      startActivity(new Intent("com337.assignment.whereami.DisplayMap")); 
     } 
    }); 

    Log.d(tag, "In the OnCreate() event"); 
} 

在地图推出的代码是：

public class DisplayMap extends MapActivity 
{ 
MapView mapView; 
MapController mc; 
GeoPoint p; 

private LocationManager lm; 
private LocationListener locationListener; 


protected class MapOverlay extends com.google.android.maps.Overlay 
{ 
    @Override 
    public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) 
    { 
     super.draw(canvas, mapView, shadow); 

     //Convert the GeoPoint to screen Pixels 
     Point screenPts = new Point(); 
     mapView.getProjection().toPixels(p, screenPts); 

     //add the marker 
     Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.pushpin5); 
     canvas.drawBitmap(bmp, screenPts.x, screenPts.y-50, null); 
     return true; 

    } 


} 

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

    mapView = (MapView) findViewById(R.id.mapView); 
    mapView.setBuiltInZoomControls(true); 
    //mapView.setStreetView(true); 
    //mapView.setSatellite(true); 

    //navigate to a point - Belfast 
    mc = mapView.getController(); 
    String coordinates[] = {"54.6000", "5.9167"}; 
    double lat = Double.parseDouble(coordinates[0]); 
    double lng = Double.parseDouble(coordinates[1]); 

    p = new GeoPoint((int) (lat*1E6), (int) (lng*1E6)); 
    mc.animateTo(p); 
    mc.setZoom(13); 

    //add a location marker 
    MapOverlay mapOverlay = new MapOverlay(); 
    List<Overlay> listOfOverlays = mapView.getOverlays(); 
    listOfOverlays.clear(); 
    listOfOverlays.add(mapOverlay); 

    lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
    locationListener = new MyLocationListener(); 

    lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener); 
    //mapView.invalidate(); 
} 

private class MyLocationListener implements LocationListener 
{ 
    public void onLocationChanged(Location loc) 
    { 
     p = new GeoPoint((int)(loc.getLatitude() * 1E6), (int)(loc.getLongitude() * 1E6)); 

     Geocoder geoCoder = new Geocoder(getBaseContext(), Locale.getDefault()); 
     try 
     { 
      List<Address> addresses = geoCoder.getFromLocation(p.getLatitudeE6()/1E6, p.getLongitudeE6()/1E6, 1); 

      String geo = ""; 
      if (addresses.size() > 0) 
      { 
       for (int i=0; i<addresses.get(0).getMaxAddressLineIndex();i++) 
        geo += addresses.get(0).getAddressLine(i) + "\n"; 
      } 
      Toast.makeText(getBaseContext(), geo, Toast.LENGTH_SHORT).show(); 
     } 
     catch (IOException e) 
     { 
      e.printStackTrace(); 
     } 

     mc.animateTo(p); 
     mc.setZoom(18); 
    } 

    public void onProviderDisabled(String provider) 
    { 

    } 

    public void onProviderEnabled(String provider) 
    { 

    } 

    public void onStatusChanged(String provider, int status, Bundle excess) 
    { 

    } 
} 

//create a method so that when the user presses the volume up/down key the map zooms in/out 
public boolean onKeyDown(int keyCode, KeyEvent event) 
{ 
    MapController mc = mapView.getController(); 
    switch(keyCode) 
    { 
    case KeyEvent.KEYCODE_VOLUME_UP:mc.zoomIn(); 
     break; 
    case KeyEvent.KEYCODE_VOLUME_DOWN:mc.zoomOut(); 
     break; 
    } 
    return super.onKeyDown(keyCode, event); 
} 

@Override 
public boolean isRouteDisplayed() 
{ 

    return false; 
} 

} 

坠机更新logcat的信息是：

12-13 16:40:49.231: W/dalvikvm(699): threadid=1: thread exiting with uncaught exception (group=0x40a13300) 
12-13 16:40:49.331: E/AndroidRuntime(699): FATAL EXCEPTION: main 
12-13 16:40:49.331: E/AndroidRuntime(699): java.lang.RuntimeException: Unable to start activity ComponentInfo{com337.assignment.whereami/com337.assignment.whereami.DisplayMap}: java.lang.NullPointerException 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.os.Looper.loop(Looper.java:137) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread.main(ActivityThread.java:4745) 
12-13 16:40:49.331: E/AndroidRuntime(699): at java.lang.reflect.Method.invokeNative(Native Method) 
12-13 16:40:49.331: E/AndroidRuntime(699): at java.lang.reflect.Method.invoke(Method.java:511) 
12-13 16:40:49.331: E/AndroidRuntime(699): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
12-13 16:40:49.331: E/AndroidRuntime(699): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
12-13 16:40:49.331: E/AndroidRuntime(699): at dalvik.system.NativeStart.main(Native Method) 
12-13 16:40:49.331: E/AndroidRuntime(699): Caused by: java.lang.NullPointerException 
12-13 16:40:49.331: E/AndroidRuntime(699): at com337.assignment.whereami.DisplayMap.onCreate(DisplayMap.java:66) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.Activity.performCreate(Activity.java:5008) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
12-13 16:40:49.331: E/AndroidRuntime(699): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
12-13 16:40:49.331: E/AndroidRuntime(699): ... 11 more 

Answer 1

您正在致电

startActivity(new Intent("com337.assignment.whereami.DisplayMap")); 

使用new Intent("com337.assignment.whereami.DisplayMap");意味着您要创建ACTION为“com337.assignment.whereami.DisplayMap”的意图。由于这是您传入的类名，而不是操作，因此不会找到活动。你是不是捕捉ActivityNotFoundException所以你会得到一个崩溃

既然你明显是想推出这个类，你不应该这样做。如果这是你的项目的一部分，你应该使用

startActivity(new Intent(YourActivityName.this, com337.assignment.whereami.DisplayMap.class)); 

或

startActivity(new Intent(getApplicationContext(), com337.assignment.whereami.DisplayMap.class)); 

可以使用意图here

Answer 2

使用上阅读了这个构造函数：

Intent(Context packageContext, Class<?> cls) 

相反，你正在使用

Intent(String action)