Java 泛型应用之打造 Android 中 ListView 和 GridView 万能适配器【CommonAdapter】-- 超简洁写法

在android中使用最多的就是ListView，GridView，用到这两个控件那么肯定要用到适配器，那就是定义一个类继承BaseAdapter，让后覆写它里面的getCount(),getView()等方法，下面来写一个demo。

1.我们来实现一个普通的ListView的Demo

• 主布局文件:activity_main.xml

• ListView的item布局:item.xml

• ListView的适配器代码:MyAdapter.java

  
      /**
       * * Created by yuandl on 2016-10-14.
       * *listView的适配器
       */
  
      public class MyAdapter extends BaseAdapter {
          private Context context;
          private List datas;
  
          public MyAdapter(Context context, List datas) {
              this.context = context;
              this.datas = datas;
          }
  
          @Override
          public int getCount() {
              return datas == null ? 0 : datas.size();
          }
  
          @Override
          public String getItem(int position) {
              return datas.get(position);
          }
  
          @Override
          public long getItemId(int position) {
              return position;
          }
  
          @Override
          public View getView(int position, View convertView, ViewGroup parent) {
              ViewHolder viewHolder;
              if (convertView == null) {
                  convertView = LayoutInflater.from(context).inflate(R.layout.item, null);
                  viewHolder = new ViewHolder();
                  viewHolder.textView = (TextView) convertView.findViewById(R.id.textView);
                  convertView.setTag(viewHolder);
              } else {
                  viewHolder = (ViewHolder) convertView.getTag();
              }
              String name = datas.get(position);
              viewHolder.textView.setText(name);
              return convertView;
          }
  
          private class ViewHolder {
              public TextView textView;
          }
      }
  

• 使用：MainActivity.java

    public class MainActivity extends Activity {
        private WebView webView;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            myAdapterTest();

        }

        /**
         * 普通适配器的方法
         */
        private void myAdapterTest() {
            setContentView(R.layout.activity_main);
            ListView listView= (ListView) findViewById(R.id.listview);
            List datas=new ArrayList<>();
            datas.add("普通适配器测试1");
            datas.add("普通适配器测试2");
            datas.add("普通适配器测试3");
            datas.add("普通适配器测试4");
            listView.setAdapter(new MyAdapter(context,datas));
        }
  }

• 看效果图

  

2.打造万能适配器第一步，万能ViewHolder–CommonViewHolder

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

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

3.打造万能适配器的最后封装–CommonAdapter

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;

import java.util.List;

/**
 * Created by yuandl on 2016-10-13.
 * 万能适配器
 */

public abstract class CommonAdapter extends BaseAdapter {
    private Context context;
    private List datas;
    private int layoutId;

    public CommonAdapter(Context context, List datas, int layoutId) {
        this.context = context;
        this.datas = datas;
        this.layoutId = layoutId;
    }

    @Override
    public int getCount() {
        return datas == null ? 0 : datas.size();
    }

    @Override
    public T getItem(int position) {
        return datas.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(layoutId, null);
        }
        T t = getItem(position);
        convertView(convertView, t);
        return convertView;
    }

    /**
     * 需要去实现的对item中的view的设置操作
     * @param item
     * @param t
     */
    protected abstract void convertView(View item, T t);

}

4.万能适配器CommonAdapter的超简洁用法

     public class MainActivity extends Activity {
        private WebView webView;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            myAdapterTest();

        }

         /**
     * 万能适配器的方法
     */
    private void commonAdapterTest() {
        setContentView(R.layout.activity_main);
        ListView listView= (ListView) findViewById(R.id.listview);
        List datas=new ArrayList<>();
        datas.add("万能适配器测试1");
        datas.add("万能适配器测试2");
        datas.add("万能适配器测试3");
        datas.add("万能适配器测试4");
        listView.setAdapter(new CommonAdapter(context,datas,R.layout.item) {

            @Override
            protected void convertView(View item, String s) {
                TextView textView=  CommonViewHolder.get(item,R.id.textView);
                textView.setText(s);
            }
        });
    }

  }

• 运行效果