关于从ListView中检索视图的困惑

Question

我试图在安卓应用程序中创建一个简单的ListView，并更改视图的背景颜色。

我只需覆盖已定义的ArrayAdapter类的getView()方法并在其中更改它，就成功了。

ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,
         android.R.layout.simple_list_item_1, Categories) {
  @Override
  public View getView(int pos, View v, ViewGroup vg) {
    View view = super.getView(pos, v, vg);

    switch (pos) {
      case 0:
        view.setBackgroundColor(Color.RED);
        break;
      case 1:
        view.setBackgroundColor(Color.BLUE);
        break;
      default:
        break;
    }

    return view;
  }
};

但是，如果我删除switch-statement并在此函数外部使用它并返回视图，则颜色不会更新。我的意思是这样的：(lv是我的ListView)

lv.setAdapter(arrayAdapter);
for (int i=0; i<2; ++i) {
  View V = (View) lv.getAdapter().getView(i, null, lv);

  switch (i) {
    case 0:
      V.setBackgroundColor(Color.RED);
      break;
    case 1:
      V.setBackgroundColor(Color.BLUE);
      break;
    default:
      break;
  }
}

它确实会返回一个对视图的引用，那么为什么它不是这样工作的呢？

Answer 1

无论何时你改变了什么，都可以打电话给：

ArrayAdapter.notifyDataSetChanged();

无论如何，这不是很好的英式方式，但我猜每个解决方案都是一个解决方案¯_(ツ)_/

Answer 2

我建议你使用RecyclerView而不是ListView。有一次，我创建了一个彩色列表。在这里，我只是复制我的代码。

public class MyListAdapter extends RecyclerView.Adapter<MyListAdapter.ViewHolder>{
    private final ArrayList<String> dataSet;

    class ViewHolder extends RecyclerView.ViewHolder {
        final TextView mTextView;
        final CardView cardView;
        ViewHolder(View v) {
            super(v);
            mTextView = (TextView) v.findViewById(R.id.info_text);
            cardView = (CardView) v.findViewById(R.id.item_container);
        }
    }

    public MyListAdapter(ArrayList<String> myDataset) {
        dataSet = myDataset;
    }

    @Override
    public MyListAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_card, parent, false);
        return new ViewHolder(view);
    }


    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.mTextView.setText(dataSet.get(position));
        switch (position%11){
            case 0: holder.cardView.setCardBackgroundColor(0xFFB71C1C);
                break;
            case 1: holder.cardView.setCardBackgroundColor(0xFF880E4F);
                break;
            case 2: holder.cardView.setCardBackgroundColor(0xFF4A148C);
                break;
            case 3: holder.cardView.setCardBackgroundColor(0xFF311B92);
                break;
            case 4: holder.cardView.setCardBackgroundColor(0xFF1A237E);
                break;
            case 5: holder.cardView.setCardBackgroundColor(0xFF01579B);
                break;
            case 6: holder.cardView.setCardBackgroundColor(0xFF004D40);
                break;
            case 7: holder.cardView.setCardBackgroundColor(0xFF1B5E20);
                break;
            case 8: holder.cardView.setCardBackgroundColor(0xFF33691E);
                break;
            case 9: holder.cardView.setCardBackgroundColor(0xFF827717);
                break;
            case 10: holder.cardView.setCardBackgroundColor(0xFFE65100);
                break;
            default: holder.cardView.setCardBackgroundColor(0xFFBF360C);
        }
    }

    @Override
    public int getItemCount() {
        return dataSet.size();
    }
}

Answer 3

您应该使用interface:在YourAdapter.class中定义一个接口：

    public interface OnColorEvent{
     void change(View v,int position)
 }

在YourAdapter.class中设置监听器：

private OnColorEvent e;
public void setOnColorEvent(OnColorEvent e)
{
this.e=e;
}

在您的getView()方法中：

    @Override
      public View getView(int pos, View v, ViewGroup vg) {
        View view = super.getView(pos, v, vg);
    if(null!=e)
    {
    e.change(v,pos);
    }
    }
In YourActivity.class:
listview.setOnColorEvent(new OnColorEvent{
@Overide
public void change(View v,int position)
{
switch (position) {
    case 0:
      V.setBackgroundColor(Color.RED);
      break;
    case 1:
      V.setBackgroundColor(Color.BLUE);
      break;
    default:
      break;
  }
}
});