Android - 从 ArrayList 中删除项目

Question

我有一个包含 6 个值的 ArrayList。当我单击一个按钮时，我删除了其中一个值，然后将一个新值添加到 ArrayList。一切正常，但是当我到达 ArrayList 中的最后一个原始项目并尝试删除它时，应用程序崩溃了。这是一个例子，

我的 ArrayList 包含这些变量 "1", "2", "3","4", "5", "6" 当我按下按钮时，ArrayList 的第一项被删除，然后又添加了一项。所以，它看起来像这样，"2", "3","4", "5", "6", "New Value" 我一直这样做，直到我到达 ArrayList 中的最后一个原始项目。看起来像这样，"6", "New Value","New Value", "New Value", "New Value", "New Value" 当我点击按钮删除项目"6" 应用程序崩溃。

这是我的 ArrayList 代码，

String[] values = new String[] { "1", "2", "3",
                "4", "5", "6" };  
        final ArrayList<String> list = new ArrayList<String>();
        for (int i = 0; i < values.length; ++i) {
          list.add(values[i]);
        }
        final StableArrayAdapter adapter = new StableArrayAdapter(this,
            R.layout.main_activity_list_item, list);
        listview.setAdapter(adapter);

这是我用来删除和添加新 ArrayList 项的代码，

Button.setOnTouchListener(new OnTouchListener(){

            public boolean onTouch(View v, MotionEvent event) {
                switch(event.getAction())
                {
                case MotionEvent.ACTION_DOWN :

                    break;
                case MotionEvent.ACTION_UP :
                    list.add("New Value");
                    list.remove(0);
                    adapter.notifyDataSetChanged();
                    break;
                }
                return false;
            }

        });

这是 StableArrayAdapter，

private class StableArrayAdapter extends ArrayAdapter<String> {

        HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();

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

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

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

      }

这是 CatLog，

03-04 00:28:01.586: E/AndroidRuntime(17775): java.lang.NullPointerException
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.example.LoginActivity$StableArrayAdapter.getItemId(LoginActivity.java:183)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.widget.AdapterView.rememberSyncState(AdapterView.java:1169)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.widget.AdapterView$AdapterDataSetObserver.onChanged(AdapterView.java:798)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.widget.AbsListView$AdapterDataSetObserver.onChanged(AbsListView.java:5630)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.database.DataSetObservable.notifyChanged(DataSetObservable.java:35)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.widget.BaseAdapter.notifyDataSetChanged(BaseAdapter.java:50)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.widget.ArrayAdapter.notifyDataSetChanged(ArrayAdapter.java:286)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.example.LoginActivity$2.onTouch(LoginActivity.java:157)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.View.dispatchTouchEvent(View.java:5574)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1965)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1734)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1965)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1734)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1965)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1734)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1965)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1734)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:1965)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1734)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1982)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1441)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.app.Activity.dispatchTouchEvent(Activity.java:2421)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1930)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.View.dispatchPointerEvent(View.java:5759)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:2970)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2529)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewRootImpl.processInputEvents(ViewRootImpl.java:869)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2538)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.os.Looper.loop(Looper.java:154)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at android.app.ActivityThread.main(ActivityThread.java:4945)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at java.lang.reflect.Method.invokeNative(Native Method)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at java.lang.reflect.Method.invoke(Method.java:511)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-04 00:28:01.586: E/AndroidRuntime(17775):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

你的代码是..

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

你会做出这样的改变..

    @Override
    public long getItemId(int position) {       
      return position;
    }

get item id 意味着它将返回一个位置这就是你将要做的一切使用这样的自定义适配器它会对你有用....

public class CustomAdapter extends ArrayAdapter<String> {

public ArrayList<String> mlist;
public Context context;
public LayoutInflater inflater;

public CustomAdapter(Context context, int resource, ArrayList<String> mlist) {
    super(context, resource);
    this.mlist = mlist;
    this.context = context;
    inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getPosition(Sample item) {
    return super.getPosition(item);
}

@Override
public Sample getItem(int position) {
    return mlist.get(position);
}

@Override
public int getCount() {
    return mlist.size();
}

@Override
public long getItemId(int position) {
    return super.getItemId(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    convertView = inflater.inflate(R.layout.listitem, null);
    TextView text1 = (TextView) convertView.findViewById(R.id.item1);       
    text1.setText(mlist.get(position).getListitem1());      
    return convertView;
}

}

Answer 2

您还需要将getItem 中的StableArrayAdapter 适配器覆盖为：

@Override
public String getItem(int position) {
    return objects.get(position);
}

因为默认getItem方法返回null

编辑：

在 Map 中添加元素是 i 的预增量，而不是 Post as：

  for (int i = 0; i < objects.size(); i++) {
    mIdMap.put(objects.get(i), i);
  }