我在BaseAdapter中出错

Question

我在我的简单应用程序中出现错误，我不知道为什么。我得到那个应用程序运行一次，但现在它只是崩溃。它不显示任何语法错误，并且一切编译都没有问题。下面的代码：

Main.java

public class Main extends ListActivity { 

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


    final List<CustomListItem> items = new ArrayList<>(3); 

    items.add(new CustomListItem (1, "Item 1", getResources().getDrawable(R.drawable.ic_launcher))); 
    items.add(new CustomListItem (2, "Item 2", getResources().getDrawable(R.drawable.ic_launcher))); 
    items.add(new CustomListItem (3, "Item 3", getResources().getDrawable(R.drawable.ic_launcher))); 


    ListAdapter adapter = new MyListItemAdapter(items, this); 
    ListView lv = getListView(); 
    lv.setAdapter(adapter); 
    lv.setTextFilterEnabled(true); 


    lv.setOnItemClickListener(new OnItemClickListener() { 
     public void onItemClick(AdapterView<?> parent, View view, 
           int position, long id) { 


      final CustomListItem item = items.get(position); 
      final int menuIndex = item.getIndex(); 
      switch (menuIndex) { 
       case 1: 
        break; 
       case 2: 
        break; 
       case 3: 
        break; 
       default: 
        break; 
      } 
     } 
    }); 
} 

MyListItemAdapter.java

公共类MyListItemAdapter延伸BaseAdapter {

private List<CustomListItem> items; 
private Context context; 
private int numItems = 0; 

public MyListItemAdapter(final List<CustomListItem> items, Context context) { 
    this.items = items; 
    this.context = context; 
    this.numItems = items.size(); 
} 

public int getCount() { 
    return numItems; 
} 

public CustomListItem getItem(int position) { 
    return items.get(position); 
} 

public long getItemId(int position) { 
    return 0; 
} 

public View getView(int position, View convertView, ViewGroup parent) { 

    final CustomListItem item = items.get(position); 

    final RelativeLayout itemLayout = (RelativeLayout) LayoutInflater.from(context).inflate(R.layout.list_item, parent, false); 

    ImageView imgIcon = (ImageView) itemLayout.findViewById(R.id.image); 
    imgIcon.setImageDrawable(item.getPicture()); 


    TextView txtLabel = (TextView) itemLayout.findViewById(R.id.txtLabel); 
    txtLabel.setText(item.getLabel()); 

    return itemLayout; 
} 

CustomListItem.java

公共类CustomListItem {

private int mIndex; 
private String mLabel; 
private Drawable mPicture; 
public CustomListItem(final int index, final String label, final Drawable pic) { 
    mIndex = index; 
    mLabel = label; 
    mPicture = pic; 
} 

public int getIndex() { 
    return mIndex; 
} 

public String getLabel() { 
    return mLabel; 
} 

public Drawable getPicture() { 
    return mPicture; 
} 

}

logcat的

14806-14806/com.robigroza.baseadaptertest E/AndroidRuntime﹕ FATAL EXCEPTION: main 
java.lang.NullPointerException at com.robigroza.baseadaptertest.MyListItemAdapter.getView(MyListItemAdapter.java:46) 
     at android.widget.AbsListView.obtainView(AbsListView.java:2465) 
     at android.widget.ListView.measureHeightOfChildren(ListView.java:1250) 
     at android.widget.ListView.onMeasure(ListView.java:1162) 
     at android.view.View.measure(View.java:15371) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4876) 
     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396) 
     at android.widget.LinearLayout.measureVertical(LinearLayout.java:681) 
     at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
     at android.view.View.measure(View.java:15371) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4876) 
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
     at android.view.View.measure(View.java:15371) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4876) 
     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396) 
     at android.widget.LinearLayout.measureVertical(LinearLayout.java:681) 
     at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
     at android.view.View.measure(View.java:15371) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4876) 
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2423) 
     at android.view.View.measure(View.java:15371) 
     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2011) 
     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1250) 
     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1425) 
     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1143) 
     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4674) 
     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) 
     at android.view.Choreographer.doCallbacks(Choreographer.java:555) 
     at android.view.Choreographer.doFrame(Choreographer.java:525) 
     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) 
     at android.os.Handler.handleCallback(Handler.java:615) 
     at android.os.Handler.dispatchMessage(Handler.java:92) 
     at android.os.Looper.loop(Looper.java:137) 
     at android.app.ActivityThread.main(ActivityThread.java:4960) 
     at java.lang.reflect.Method.invokeNative(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:511) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805) 
     at dalvik.system.NativeStart.main(Native Method) 

Answer 1

由于getView需要返回查看试试这个：

public View getView(int position, View convertView, ViewGroup parent) { 

    View rootView = convertView; 
    if(rootView == null){ 


     LayoutInflater inflater = (LayoutInflater)LayoutInflater.from(context); 
     rootView = inflater.inflate(R.layout.list_item, parent, false); 

     final CustomListItem item = items.get(position); 

    } 

    if(item != null){ 
     ImageView imgIcon = (ImageView) rootView.findViewById(R.id.image); 
     imgIcon.setImageDrawable(item.getPicture()); 


     TextView txtLabel = (TextView) rootView.findViewById(R.id.txtLabel); 
     txtLabel.setText(item.getLabel()); 
    } 


    return rootView; 
} 

试试这个希望它帮助！

Answer 2

如果是在getView大概的要素之一的（在线路46）不会在此布局存在。