Question

我的简单应用内部出错，我不知道为什么。我让那个应用程序运行一次，但现在它只是崩溃了。它没有显示任何语法错误，一切都编译没有问题。这是代码：

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扩展了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

如果它在getView中，则此布局中可能不存在其中一个元素（第46行的元素）。

Answer 2

由于getView需要返回一个View，请尝试：

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;
}

试试这个希望它有帮助!!!

我在BaseAdapter中遇到错误

2 个答案: