Android基础--ListView的复用机制

RecycleBin 机制

RecycleBin 缓存机制如图：

RecycleBin 代码实现：其实就是BaseAdapter中的getView方法的第二个参数convertView复用代码如下：这是两种样式的item的复用

@Override
    public View getView(int position, View convertView, ViewGroup viewGroup) {
        LayoutInflater inflater = LayoutInflater.from(viewGroup.getContext());
        if (getItemViewType(position) == ViewType.TEXT){
            if (convertView == null){
                convertView = inflater.inflate(R.layout.text_message_item,viewGroup,false);
            }
            TextView textView = convertView.findViewById(R.id.message_content);
            TextMessage textMessage = (TextMessage)messageList.get(position);
            textView.setText(textMessage.getText());
        }else {
            if (convertView == null){
                convertView = inflater.inflate(R.layout.image_message_item,viewGroup,false);
            }
            ImageView imageView = convertView.findViewById(R.id.image_head);
            ImageMessage imageMessage = (ImageMessage)messageList.get(position);
            imageView.setImageResource(imageMessage.getImage());
        }
        return convertView;
    }

ViewHolder机制

如上面代码中每次都会去findViewById这项操作，findViewById其实是很耗时的一个操作，ViewHolder机制就是把findViewById的结果缓存起来，例子中有两ViewHolder : ViewHolderText 与 ViewHolderImage对应两种item

public class MyBaseAdapter extends BaseAdapter {

    private static final int ViewTypeCount = 2;
    private interface ViewType {
        int TEXT = 0;
        int IMAGE = 1;
    }


    private List