Android之ListView的Adapter的复用

小鱼儿 2022-08-18 15:16 262阅读 0赞

在Android开发中一个项目需要在很多地方使用的ListView。既然使用了ListView则不可避免的使用了Adapter，重复写逻辑几乎相同的Adapter也是一件枯燥的事，下面来研究如何复用Adapter.  
使用了ListView的两个地方(模拟代码):

一.//第一个ListView
    listView.setAdapter(new MyAdapter());
     class MyAdapter extends BaseAdapter{
        
        //arrayList是设置给ListView数据的集合
           @Override
           public int getCount() {
               return arrayList.size();
           }
    
           @Override
           public Object getItem(int i) {
               return arrayList.get(i);
           }
    
           @Override
           public long getItemId(int i) {
               return i;
           }
    
           @Override
           public View getView(int i, View view, ViewGroup viewGroup) {
              ViewHolder  viewHolder =null;
               if(view == null){
                   view = View.inflate(ThemeFragment.this.getActivity(), R.layout.theme_adapt_item,null);
                   viewHolder = new ViewHolder();
                   viewHolder.icon = (ImageView) view.findViewById(R.id.theme_iv);
                   viewHolder.textView = (TextView) view.findViewById(R.id.theme_text);
                   view.setTag(viewHolder);
               }else{
                   viewHolder = (ViewHolder) view.getTag();
               }
               //给ViewHolder设置值，即给ListView的各个组件设置值
               BitmapHelper.getBitmapUtils().display(viewHolder.icon, GlobalUrl.ICON_URL+theme.themeInfos.get(i).url);
               viewHolder.textView.setText(theme.themeInfos.get(i).des);
               return view;
           }
       }
       //为了优化ListView不可避免的使用了ViewHolder来复用
        static class ViewHolder{
        
           ImageView  icon;
           TextView   textView;
        }

二.//第二个ListView
    
    listView.setAdapter(new MyAdapter());
     class MyAdapter extends BaseAdapter{
        
        //arrayList是设置给ListView数据的集合
           @Override
           public int getCount() {
               return arrayList.size();
           }
    
           @Override
           public Object getItem(int i) {
               return arrayList.get(i);
           }
    
           @Override
           public long getItemId(int i) {
               return i;
           }
    
           @Override
           public View getView(int i, View view, ViewGroup viewGroup) {
              ViewHolder  viewHolder =null;
               if(view == null){
                   view = View.inflate(HomeFragment.this.getActivity(), R.layout.home_adapt_item, null);
                   viewHolder = new ViewHolder();
               viewHolder.item_icon = (ImageView) view.findViewById(R.id.item_icon);
               viewHolder.app_name = (TextView) view.findViewById(R.id.item_title);
               viewHolder.app_size = (TextView) view.findViewById(R.id.item_size);
               viewHolder.app_introduce = (TextView) view.findViewById(R.id.item_bottom);
                   view.setTag(viewHolder);
               }else{
                   viewHolder = (ViewHolder) view.getTag();
               }
               //给ViewHolder设置值，即给ListView的各个组件设置值
          BitmapHelper.getBitmapUtils().display(this.item_icon, GlobalUrl.ICON_URL + detailAppInfos.iconUrl);
               this.app_name.setText(detailAppInfos.name);
               this.app_size.setText(detailAppInfos.size);
               this.app_introduce.setText(detailAppInfos.des);
               return view;
           }
       }
       //为了优化ListView不可避免的使用了ViewHolder来复用
        static class ViewHolder{
        
           ImageView item_icon;
           TextView app_name;
           TextView app_size;
           TextView app_introduce;
        }

如上两段代码是在开发过程中经常使用到的，现在对Adapter进行抽取封装:  
1.首先Adapter的前三个方法:getCount(),getItem(),getItemId()是完全一样的，通过一个ArrayList来完成。我们抽取的Adapter让子类注入一个ArrayList进来:

public class DefaultAdapter<T> extends BaseAdapter {
        private List<T> listData;
        public DefaultAdapter(List<T> list){
             this.listData = list;
        }
        @Override
        public int getCount() {
            return listData.size();
        }
    
        @Override
        public Object getItem(int i) {
            return listData.get(i);
        }
    
        @Override
        public long getItemId(int i) {
            return i;
        }
    
        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            return null;
        }
    }

2.此时Adapter中的getView()显示的很臃肿，为了getView()方法的简介，将getView()方法与为了复用的ViewHolder进行进一步修改(针对第二个ListView):

Adapter:

class MyAdapter extends DefaultAdapter<HomeInfos.DetailAppInfos>{
        
    
    
            public MyAdapter(List<HomeInfos.DetailAppInfos> list) {
                super(list);
            }
    
            @Override
            public View getView(int i, View view, ViewGroup viewGroup) {
                ViewHolder viewHolder = null;
                if(view==null){
                //所有的初始化view的方法全部放在ViewHolder的构造方法中
                    viewHolder = new ViewHolder();
                }else{
                    viewHolder = (ViewHolder) view.getTag();
                }
                //设置数据的方法也放在viewHolder中，而设置的具体数据(集合中的数据)注入进去
                viewHolder.setDetailInfos(homeInfos.list.get(i));
                return viewHolder.getView();
            }
        }

ViewHolder:

static class ViewHolder{
           ImageView item_icon;
           TextView app_name;
           TextView app_size;
           TextView app_introduce;
           //显示的每个条目的View
           private   View view;
           private  BitmapUtils bitmapUtils;
           //集合中的数据，设置给每个ListView条目的
           private HomeInfos.DetailAppInfos detailAppInfos;
           //注入的方法
           public void setDetailInfos(HomeInfos.DetailAppInfos detailAppInfos) {
               this.detailAppInfos = detailAppInfos;
              //注入成功后,刷新view。刷新view即是把集合中的数据设置给viewHolder
               refreshView();
           }
    
           public ViewHolder(){
               bitmapUtils = BitmapHelper.getBitmapUtils();
               view = View.inflate(UiUtil.getContext(), R.layout.home_adapt_item, null);
               this.item_icon = (ImageView) view.findViewById(R.id.item_icon);
               this.app_name = (TextView) view.findViewById(R.id.item_title);
               this.app_size = (TextView) view.findViewById(R.id.item_size);
               this.app_introduce = (TextView) view.findViewById(R.id.item_bottom);
               view.setTag(this);
           }
    
           public View getView() {
               return view;
           }
           //集合中的数据设置给viewHolder
           public void refreshView(){
               BitmapHelper.getBitmapUtils().display(this.item_icon, GlobalUrl.ICON_URL + detailAppInfos.iconUrl);
               this.app_name.setText(detailAppInfos.name);
               this.item_rating.setRating((float) detailAppInfos.stars);
               this.app_size.setText(detailAppInfos.size);
               this.app_introduce.setText(detailAppInfos.des);
    
           }
    
        }

3.将两个ListView都做如上操作之后会发现，getView变得极其相似了，那么我们可以把它提取到分类中:  
此时就会发现一个问题，每个ListView的ViewHolder都不一样，所以我们把ViewHolder与进一部的进行抽象(针对第二个ListView):  
BaseViewHolder：

public abstract class BaseViewHolder<T> {
    
        private View view;
        private BitmapUtils bitmapUtils;
        private T detailInfos;
    
        public void setDetailInfos(T detailInfos) {
            this.detailInfos = detailInfos;
            refreshView(detailInfos);
        }
    
        public BaseViewHolder(){
            bitmapUtils = BitmapHelper.getBitmapUtils();
            view = initView();
            view.setTag(this);
        }
       public abstract View   initView();
    
        public View getView() {
            return view;
        }
        public abstract void refreshView(T detailInfos);
    
    }

经过抽取之后:每个ViewHolder只需要实现两个抽象方法

static class ViewHolder extends BaseViewHolder<HomeInfos.DetailAppInfos>{
           ImageView item_icon;
           TextView app_name;
           RatingBar item_rating;
           TextView app_size;
           TextView app_introduce;
    
           @Override
           public View initView() {
               View   view = View.inflate(UiUtil.getContext(), R.layout.home_adapt_item, null);
               this.item_icon = (ImageView) view.findViewById(R.id.item_icon);
               this.app_name = (TextView) view.findViewById(R.id.item_title);
               this.item_rating = (RatingBar) view.findViewById(R.id.item_rating);
               this.app_size = (TextView) view.findViewById(R.id.item_size);
               this.app_introduce = (TextView) view.findViewById(R.id.item_bottom);
               return  view;
           }
           @Override
           public void refreshView(HomeInfos.DetailAppInfos detailAppInfos){
               BitmapHelper.getBitmapUtils().display(this.item_icon, GlobalUrl.ICON_URL + detailAppInfos.iconUrl);
               this.app_name.setText(detailAppInfos.name);
               this.item_rating.setRating((float) detailAppInfos.stars);
               this.app_size.setText(detailAppInfos.size);
               this.app_introduce.setText(detailAppInfos.des);
    
           }
    
        }

4.此时，把getView()提取到抽象中:  
对于每个ViewHolder也有了BaseViewHolder,但在getView()中生成具体的ViewHodler时不知道生成哪一个，所以可以定义一个获取子类ViewHolder的抽象方法，让子类返回一个自身的ViewHolder的实现(这儿类似与DAO设计模式中BaseServiceImpl声明一个抽象方法，让子类返回自身Dao的实现因为BaseServiceImpl不知道使用哪个Dao来完成，只能丢给子类来处理).

最终的代码(针对第二个ListView):

class MyAdapter extends DefaultAdapter<HomeInfos.DetailAppInfos>{
        
    
    
            public MyAdapter(List<HomeInfos.DetailAppInfos> list) {
                super(list);
            }
    
            @Override
            protected BaseViewHolder getViewHolder() {
                return new ViewHolder();
            }
    
    
        }
       static class ViewHolder extends BaseViewHolder<HomeInfos.DetailAppInfos>{
        
           ImageView item_icon;
           TextView app_name;
           TextView app_size;
           TextView app_introduce;
    
           @Override
           public View initView() {
               View   view = View.inflate(UiUtil.getContext(), R.layout.home_adapt_item, null);
               this.item_icon = (ImageView) view.findViewById(R.id.item_icon);
               this.app_name = (TextView) view.findViewById(R.id.item_title);
               this.app_size = (TextView) view.findViewById(R.id.item_size);
               this.app_introduce = (TextView) view.findViewById(R.id.item_bottom);
               return  view;
           }
           @Override
           public void refreshView(HomeInfos.DetailAppInfos detailAppInfos){
               BitmapHelper.getBitmapUtils().display(this.item_icon, GlobalUrl.ICON_URL + detailAppInfos.iconUrl);
               this.app_name.setText(detailAppInfos.name);
               this.app_size.setText(detailAppInfos.size);
               this.app_introduce.setText(detailAppInfos.des);
    
           }
    
        }

抽象的两个类Adapter和ViewHolder:

public abstract class DefaultAdapter<T> extends BaseAdapter {
        private List<T> listData;
        public DefaultAdapter(List<T> list){
             this.listData = list;
        }
        @Override
        public int getCount() {
            return listData.size();
        }
    
        @Override
        public Object getItem(int i) {
            return listData.get(i);
        }
    
        @Override
        public long getItemId(int i) {
            return i;
        }
    
        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            BaseViewHolder viewHolder =null;
            if(view == null){
    
                viewHolder = getViewHolder();
    
            }else{
                viewHolder = (BaseViewHolder) view.getTag();
            }
            viewHolder.setDetailInfos(listData.get(i));
            return viewHolder.getView();
        }
        protected  abstract BaseViewHolder getViewHolder();
    }

这样就完成了ListView设置Adapter的抽象，以后需要使用Adapter的地方直接让Adapter继承DefaultAdapter。让ViewHolder实现BaseViewHolder，然后分别实现父类定义的抽象方法(Adapter实现返回自己ViewHolder的方法，ViewHolder实现生成每个条目的View方法和给这个View设置数据的方法)即可。