的Android getApplicationContext NullPointerException异常

Question

我试图通过保存应用程序上下文的位置，所以我做了以下内容：

对myApp类：

进口android.app.Application;

import com.google.android.maps.GeoPoint;

public class myApp extends Application { 

    private GeoPoint Tunis = new GeoPoint(microdegrees(36.827589),microdegrees(10.171165)); 
    private GeoPoint myLocation=Tunis; 

    public GeoPoint getMyLocation(){ 
    return myLocation; 
    } 
    public void setMyLocation(GeoPoint s){ 
    myLocation = s; 
    } 
    private int microdegrees(double value){ 
    return (int)(value*1000000); 
    } 

} 

我的清单：

<application android:icon="@drawable/icon" android:label="@string/app_name" android:name=".myApp"> 
     <uses-library android:name="com.google.android.maps"/> 
     <activity android:name=".Main" 
        android:label="@string/app_name"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 
       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 

    </application> 

，在我的主要活动我这样做：

myApp appState = ((myApp)getApplicationContext()); 

，这将导致一个NullPointerException当我启动应用程序:(可以请你告诉我为什么会发生这种异常？我认为在myApp类中，我将MyLocation初始化为现有的GeoPoint？

个谢谢，

Answer 1

我的打扰对不起，我解决了这个由： 1添加构造函数来对myApp：

public class myApp extends Application { 

    public GeoPoint Tunis = new GeoPoint(microdegrees(36.827589),microdegrees(10.171165)); 
    public GeoPoint myLocation; 

    public myApp(){ 
     super(); 
     myLocation=Tunis; 
    } 
    public GeoPoint getMyLocation(){ 
    return myLocation; 
    } 
    public void setMyLocation(GeoPoint s){ 
    myLocation = s; 
    } 
    private int microdegrees(double value){ 
     return (int)(value*1000000); 
    } 
} 

2-声明在我的主要活动如下中的onCreate无效

appState = ((myApp)getApplicationContext()); 

这样的：

public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
     GeoPoint Tunis = new GeoPoint(microdegrees(36.827589),microdegrees(10.171165)); 
     MyMap=(MapView)findViewById(R.id.MyGMap); 
     MyMap.setBuiltInZoomControls(true); 
     MyController=MyMap.getController(); 
     MyController.setZoom(12); 
     MyController.setCenter(Tunis); 
     appState = ((myApp)getApplicationContext()); 

感谢