错误与空指针

Question

我得到空例外错误，我需要一些帮助来弄明白，我试图更新我的清单和它看起来不错，但仍然得到错误

这里是logcat的

03-09 16:00:53.803: E/JSON(540): {"tag":"login","success":1,"error":0,"uid":"513b5349d86546.88432881","user":{"name":"p","email":"p","created_at":"2013-03-09 23:20:41","updated_at":null}} 
03-09 16:00:54.863: E/AndroidRuntime(540): FATAL EXCEPTION: main 
03-09 16:00:54.863: E/AndroidRuntime(540): java.lang.RuntimeException: Unable to start activity  ComponentInfo{com.mohammed.watzIslam/com.mohammed.watzIslam.maincontentview}: java.lang.NullPointerException 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.os.Handler.dispatchMessage(Handler.java:99) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.os.Looper.loop(Looper.java:123) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread.main(ActivityThread.java:4627) 
03-09 16:00:54.863: E/AndroidRuntime(540): at java.lang.reflect.Method.invokeNative(Native Method) 
03-09 16:00:54.863: E/AndroidRuntime(540): at java.lang.reflect.Method.invoke(Method.java:521) 
03-09 16:00:54.863: E/AndroidRuntime(540): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
03-09 16:00:54.863: E/AndroidRuntime(540): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
03-09 16:00:54.863: E/AndroidRuntime(540): at dalvik.system.NativeStart.main(Native Method) 
03-09 16:00:54.863: E/AndroidRuntime(540): Caused by: java.lang.NullPointerException 
03-09 16:00:54.863: E/AndroidRuntime(540): at com.mohammed.watzIslam.maincontentview.onCreate(maincontentview.java:28) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
03-09 16:00:54.863: E/AndroidRuntime(540): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
03-09 16:00:54.863: E/AndroidRuntime(540): ... 11 more 

，这是不能发动

import android.app.Activity; 
import android.content.ActivityNotFoundException; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 

public class maincontentview extends Activity { 

public void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 

    String[] contentarray = getResources().getStringArray(R.array.contnarr); 
    this.setListAdapter(new ArrayAdapter<String>(this, R.layout.maincontentview, R.id.label1, contentarray)); 




ListView lv = getListView(); 

// listening to single list item on click 
lv.setOnItemClickListener(new OnItemClickListener() { 
    public void onItemClick(AdapterView<?> parent, View view, 
     int position, long id) { 
     // start different activities 
     switch(position){ 
     case 0: 
     Intent txt = new Intent(view.getContext(),TextA.class); 

      try{ 
      startActivity(txt); 
      } catch(ActivityNotFoundException e) { 
      e.printStackTrace(); 
      } 
      break; 
     case 1: 
     Intent video = new Intent(view.getContext(),Videos.class); 
      try{ 
      startActivity(video); 
      }catch(ActivityNotFoundException e){ 
      e.printStackTrace(); 
      } 
      break; 

     default: break; 

     }   



} 
}); 
} 

    private ListView getListView() { 
    // TODO Auto-generated method stub 
    return null; 
    } 

    private void setListAdapter(ArrayAdapter<String> arrayAdapter) { 
    // TODO Auto-generated method stub 

    } 

} 

终于首席清单

0我的Java文件

Answer 1

您正在将课程从Activity扩展到现在仍在使用getListView()。

getListView（）仅在使用时使用ListActivity。对于普通的Activity，您需要使用setContentView（View）来生成布局。

看到你的代码，我想你应该使用一个ListActivity。

public class maincontentview extends ListActivity