Java 泛型应用之打造 Android 万能 ViewHolder - 超简洁写法

在ListView的Adapter中的getView()方法中的繁琐写法

@Override  
public View getView(int position, View convertView, ViewGroup parent) {  
    ViewHolder viewHolder = null;
    if (convertView == null) {  
        convertView = LayoutInflater.from(context)  
          .inflate(R.layout.item, parent, false);  
          viewHolder = new ViewHolder();
          viewHolder.name = (TextView) convertView.findViewById(R.id.name);
           convertView.setTag(viewHolder);
    }else{
            viewHolder = (ViewHolder) convertView.getTag();
        }

  viewHolder.name.setText("sss"); 

    return convertView;  
}  
private static class ViewHolder
    {
        TextView name;
    }

先了解一下SparseArray

SparseArray(稀疏数组).他是Android内部特有的api,标准的jdk是没有这个类的.在Android内部用来替代HashMap这种形式,使用SparseArray更加节省内存空间的使用,SparseArray也是以key和value对数据进行保存的.使用的时候只需要指定value的类型即可.并且key不需要封装成对象类型.

最后经过优化和简化后的代码

/**
 * Created by yuandl on 2016-10-13.
 */

import android.util.SparseArray;
import android.view.View;

/**
 * 万能的ViewHolder
 *
 * @author
 */
public class CommonViewHolder {
    /**
     * @param view 所有缓存View的根View
     * @param id   缓存View的唯一标识
     * @return
     */
    public static  T get(View view, int id) {

        SparseArray viewHolder = (SparseArray) view.getTag();
        
        if (viewHolder == null) {
            viewHolder = new SparseArray();
            view.setTag(viewHolder);
        }
        View chidlView = viewHolder.get(id);
        if (chidlView == null) {
            
            chidlView = view.findViewById(id);
            viewHolder.put(id, chidlView);
        }
        return (T) chidlView;
    }
}

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

    if (convertView == null) {  
        convertView = LayoutInflater.from(context)  
          .inflate(R.layout.item, parent, false);  
    }  

    TextView name= ViewHolder.get(convertView, R.id.name);  

    name.setText("sss");  

    return convertView;  
}