Question

我正在创建ListView，每行包含两个元素（一个用于打开第二行以删除行）。我在主要活动中创建了我自定义的ListView，如下所示：

ArrayList<String> names = Devices.getInstance().getNameList();

final StableArrayAdapter adapter = new StableArrayAdapter(this,listViewResourceId,names);
final ListView listview = (ListView) findViewById(R.id.listView1);
listview.setAdapter(adapter);

我自己的ArrayAdapter：

private class StableArrayAdapter extends ArrayAdapter<String> {

    HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();
    private final Activity mContext;

    public StableArrayAdapter(Activity context, int textViewResourceId, List<String> objects) {
      super(context, textViewResourceId, objects);
      mContext = context;
      for (int i = 0; i < objects.size(); ++i) {
        mIdMap.put(objects.get(i), i);
      }
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
      View view = null;
      if (convertView == null) {
        LayoutInflater inflator = mContext.getLayoutInflater();
        view = inflator.inflate(R.layout.row, null);
        final ViewHolder viewHolder = new ViewHolder();
        viewHolder.text = (TextView) view.findViewById(R.id.label);
        viewHolder.text.setText(getItem(position));
        viewHolder.button = (ImageButton) view.findViewById(R.id.del);
        viewHolder.button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO dodanie zapytania o usuniecie
                StableArrayAdapter.this.mIdMap.remove(getItem(position));
                StableArrayAdapter.this.notifyDataSetChanged();
                //((BaseAdapter) ((ListView)findViewById(R.id.listView1)).getAdapter()).notifyDataSetChanged(); 
            }

        });
        view.setTag(viewHolder);
      }

      return view;
    }

    @Override
    public long getItemId(int position) {
      String item = getItem(position);
      return mIdMap.get(item);
    }

    @Override
    public boolean hasStableIds() {
      return true;
    }

  }

问题是，当我尝试使用删除按钮删除行时（其上面的单击侦听器在上面），在notifyDataSetChanged（）行上有 NullPointerException。

我尝试制作非匿名类（对于OnClickListener），或者将本地字段从OnCreate切换到类字段但没有任何效果 - 我想我做了一些愚蠢的事情但是现在我是盲目的，看不到任何东西在这段代码中。

先谢谢你的帮助!!!

堆栈跟踪：

07-02 10:24:26.604: E/AndroidRuntime(2109): FATAL EXCEPTION: main 07-02 10:24:26.604: E/AndroidRuntime(2109): java.lang.NullPointerException 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.AbsListView.obtainView(AbsListView.java:2253) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.ListView.makeAndAddView(ListView.java:1769) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.ListView.fillSpecific(ListView.java:1318) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.ListView.layoutChildren(ListView.java:1600) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.AbsListView.onLayout(AbsListView.java:2102) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1649) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1507) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.LinearLayout.onLayout(LinearLayout.java:1420) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.FrameLayout.onLayout(FrameLayout.java:448) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.FrameLayout.onLayout(FrameLayout.java:448) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.FrameLayout.onLayout(FrameLayout.java:448) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.widget.FrameLayout.onLayout(FrameLayout.java:448) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.View.layout(View.java:13754) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewGroup.layout(ViewGroup.java:4362) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1866) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1687) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.Choreographer.doCallbacks(Choreographer.java:555) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.Choreographer.doFrame(Choreographer.java:525) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.os.Handler.handleCallback(Handler.java:615) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.os.Handler.dispatchMessage(Handler.java:92) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.os.Looper.loop(Looper.java:137) 07-02 10:24:26.604: E/AndroidRuntime(2109): at android.app.ActivityThread.main(ActivityThread.java:4745) 07-02 10:24:26.604: E/AndroidRuntime(2109): at java.lang.reflect.Method.invokeNative(Native Method) 07-02 10:24:26.604: E/AndroidRuntime(2109): at java.lang.reflect.Method.invoke(Method.java:511) 07-02 10:24:26.604: E/AndroidRuntime(2109): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 07-02 10:24:26.604: E/AndroidRuntime(2109): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 07-02 10:24:26.604: E/AndroidRuntime(2109): at dalvik.system.NativeStart.main(Native Method)

Answer 1

你正在if (convertView == null) {}区内做所有事情。仅用于向持有者充气和存储视图。设置文本并单击此块外部的侦听器，以便它们应用于每个视图，重新循环或不重新循环。

示例：

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

    //--init if not re-cycled--
    if (convertView == null) {
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.row, parent, false);
        convertView.setTag(new ViewHolder(
                (TextView) convertView.findViewById(R.id.label),
                (ImageButton) convertView.findViewById(R.id.del)
        ));
    }

    //--data to set--
    String item = getItem(position);

    View.OnClickListener listener = new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            StableArrayAdapter.this.mIdMap.remove(getItem(position));
            StableArrayAdapter.this.notifyDataSetChanged();
        }
    };

    //--set data--
    ViewHolder holder = (ViewHolder) convertView.getTag();
    holder.text.setText(item);
    holder.button.setOnClickListener(listener);
    return convertView;
}

private static class ViewHolder{
    public final TextView text;
    public final Button button;

    private ViewHolder(TextView text, Button button) {
        this.text = text;
        this.button = button;
    }
}

Answer 2

试试这个，

@Override
    public View getView(final int position, View convertView, ViewGroup parent) {
//      View view = null;         remove this line
      if (convertView == null) {
        LayoutInflater inflator = mContext.getLayoutInflater();
        view = inflator.inflate(R.layout.row, null);
      }
    final ViewHolder viewHolder = new ViewHolder();
    viewHolder.text = (TextView) convertView.findViewById(R.id.label);
    viewHolder.text.setText(getItem(position));
    viewHolder.button = (ImageButton) convertView.findViewById(R.id.del);
    viewHolder.button.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO dodanie zapytania o usuniecie
            StableArrayAdapter.this.mIdMap.remove(getItem(position));
            StableArrayAdapter.this.notifyDataSetChanged();
            //((BaseAdapter) ((ListView)findViewById(R.id.listView1)).getAdapter()).notifyDataSetChanged(); 
        }

    });
    view.setTag(viewHolder);
  }

  return view;
}

Answer 3

问题当然是愚蠢的，我试图通过从容器中删除它来删除行，而没有正确通知这个整个类StableArrayAdapter，而不是这个（在OnClickListener中）：

StableArrayAdapter.this.mIdMap.remove(getItem(position));

我应该用这个：

StableArrayAdapter.this.remove(getItem(position));

notifyDataSetChanged（）导致NullPointerException

3 个答案: