api v2 中的 mapview 和 cameraupdate

Posted 2023-04-14

【中文标题】api v2 中的 mapview 和 cameraupdate

【英文标题】：mapview and cameraupdate in api v2

【发布时间】：2012-12-04 00:31:21

【问题描述】：

为什么 CameraUpdateFactory 类在我的项目中不起作用？ 如果执行以下命令，应用程序会崩溃： CameraUpdate pino= CameraUpdateFactory.newLatLng(new LatLng(location.getLatitude(), location.getLongitude())); 如果我删除该行（当然还有下一行），代码会成功启动并显示地图。 我需要 mapView 并且需要使用新的 api v2。 我以这种方式在布局中声明mapView：

        <com.google.android.gms.maps.MapView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:map="http://schemas.android.com/apk/res-auto"

    android:id="@+id/mappa"
    android:layout_
    android:layout_
    android:layout_alignParentBottom="true"
    android:layout_below="@+id/buttonBar"

    map:uiZoomControls="false"
     />

然后在 mainActivity.java 我写了这个：

    public class MainActivity extends FragmentActivity    implements LocationListener, LocationSource  
public static boolean locatingMe=true;
public GoogleMap mappa;
public MapView mapView;
private OnLocationChangedListener onLocationChangedListener;
private LocationManager locationManager;




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

    mapView = (MapView) findViewById(R.id.mappa);
    mapView.onCreate(savedInstanceState);


        locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

    //You may want to pass a different provider in as the first arg here
    //depending on the location accuracy that you desire
    //see LocationManager.getBestProvider()
    Criteria locationCriteria = new Criteria();
    locationCriteria.setAccuracy(Criteria.NO_REQUIREMENT);
    locationManager.requestLocationUpdates(locationManager.getBestProvider(locationCriteria, true), 1L, 2F, this);

    if (mappa == null) 
        mappa=mapView.getMap();
        //This is how you register the LocationSource
        mappa.setLocationSource(this);
        mappa.getUiSettings().setMyLocationButtonEnabled(false);
        mappa.setMyLocationEnabled(true);
    



@Override
public void onPause()

    if(locationManager != null)
    
        locationManager.removeUpdates(this);
    
    mapView.onPause();
    super.onPause();


@Override
public void onResume()

      checkGooglePlayServicesAvailability();
      checkGps();
      mapView.onResume();
      super.onResume();

@Override
protected void onDestroy() 
    mapView.onDestroy();
    super.onDestroy();


@Override
public void onLowMemory() 
    super.onLowMemory();
    mapView.onLowMemory();


@Override
public void activate(OnLocationChangedListener listener) 

    onLocationChangedListener = listener;


@Override
public void deactivate() 

    onLocationChangedListener = null;


@Override
public void onLocationChanged(Location location) 

    if( onLocationChangedListener != null )
    
        onLocationChangedListener.onLocationChanged( location );

        //Move the camera to the user's location once it's available!
        //only if locatingMe is true
        if (locatingMe) 
            if (mappa!=null)
                CameraUpdate pino= CameraUpdateFactory.newLatLng(new LatLng(location.getLatitude(), location.getLongitude()));
                        mappa.animateCamera(pino);

            

        

    


@Override
public void onProviderDisabled(String provider) 

    // TODO Auto-generated method stub
    Toast.makeText(this, "provider disabled", Toast.LENGTH_SHORT).show();


@Override
public void onProviderEnabled(String provider) 

    // TODO Auto-generated method stub
    Toast.makeText(this, "provider enabled", Toast.LENGTH_SHORT).show();


@Override
public void onStatusChanged(String provider, int status, Bundle extras) 

    // TODO Auto-generated method stub
    Toast.makeText(this, "status changed", Toast.LENGTH_SHORT).show();

LogCat 中的错误如下：

 Caused by: java.lang.NullPointerException: CameraUpdateFactory is not initialized.

【参考方案1】：

我通过在“onCreate”上添加以下几行来解决问题：

 try 
     MapsInitializer.initialize(this);
  catch (GooglePlayServicesNotAvailableException e) 
     e.printStackTrace();
 

原因是 CameraUpdateFactory 需要被初始化（即使从文档看来使用 mapview 它应该被自动初始化）

我什至将“public class MainActivity extends FragmentActivity”替换为“public class MainActivity extends Activity”。但我认为这最后一件事是不需要的..

【讨论】：

我也是！非常感谢！

if (MapsInitializer.initialize(ctx) != ConnectionResult.SUCCESS) // 处理错误

【参考方案2】：

如果我使用：

try 
 MapsInitializer.initialize(this);
 catch (GooglePlayServicesNotAvailableException e) 
 e.printStackTrace();

异常给我这个错误：

Unreachable catch block for GooglePlayServicesNotAvailableException.

try 语句体永远不会抛出此异常。

我只用过：

MapsInitializer.initialize(this);

:)