xamarin android 打造ListView万能适配器

来源：互联网发布：东汉末年知乎编辑：程序博客网时间：2024/06/05 08:08

早些时候接触xamarin android 的列表，写了很多ListView的Adapter，建一个ListView就写一个Adapter,每一个Adapter里面还有去写一个ViewHolder的类来优化，自从看了hongyang博客的listview万能适配器的文章，学习良多，所以就写篇关于xamarin android ListView通用适配器的文章。

本章主要分为以下三点：

打造通用的ViewHolder优化ListView性能
使用泛型Adapter适应不同布局的ListView
C#委托和Java匿名内部类的比较

打造通用的ViewHolder优化ListView性能

  public  class ViewHolder:Java.Lang.Object    {        private  SparseArray<View>  Views;         View ConvertView;        private Context context ;         int mPosition;        private ViewHolder(Context _context,ViewGroup  parent ,int itemLayoutId,int position)        {            this.mPosition = position;            Views = new SparseArray<View>();            ConvertView =  LayoutInflater.From(_context).Inflate(itemLayoutId,null);            ConvertView.Tag = this;        }        public static ViewHolder Get(Context context , View convertView,ViewGroup  parent ,int itemLayoutId,int position)        {            if (convertView == null)            {                return new ViewHolder(context, parent, itemLayoutId, position);            }            else            {                ViewHolder holder = (ViewHolder)convertView.Tag;                holder.mPosition = position;                return holder;            }        }        public T GetView<T>(int viewId) where T :View        {            View view = Views.Get(viewId);            if (view == null)            {                view = ConvertView.FindViewById<T>(viewId);                Views.Put(viewId,view);            }            return (T)view;        }        public View GetConvertView()        {            return ConvertView;        }        /// <summary>        /// 给TextView 设置文本        /// </summary>        /// <param name="viewId"></param>        /// <param name="text"></param>        /// <returns></returns>        public ViewHolder SetText(int viewId ,string  text)        {            TextView view = GetView<TextView>(viewId);            view.Text = text;            return this;        }        /// <summary>        /// 给ImageView 设置图片        /// </summary>        public ViewHolder SetImageBitMap(int viewId , Bitmap bm)        {            ImageView view = GetView<ImageView>(viewId);            view.SetImageBitmap(bm);            return this;        }    }

稍微解释一下：
ViewHolder的构造方法中初始化变量，并将ListView的布局view的Tag设置成viewholder的实例
Get方法使用单例模式初始化ViewHolder
GetView泛型方法获取ListView布局中的空间
SetText、SetImageBitMap给一些常用的控件复值

使用泛型Adapter适应不同布局的ListView

CommonAdapter是一个泛型的基类，一些重复的重写方法都在这个基类，然后我们写一个子类继承这个CommonAdapter，就简化了很多代码

 public abstract class CommonAdapter<T> :BaseAdapter    {        Context mContext;         List<T> mData;         int mItemLayoutId;        public CommonAdapter(Context context, List<T> data, int itemLayoutId):base()        {            this.mContext = context;            mData = data;            mItemLayoutId = itemLayoutId;        }        public override int Count        {            get            {                return mData.Count;            }        }        public override  Java.Lang.Object GetItem(int position)        {            return null;        }        public override long GetItemId(int position)        {            return position;        }        public override View GetView(int position, View convertView, ViewGroup parent)        {            var item = mData[position];            ViewHolder viewHolder = ViewHolder.Get(mContext, convertView, parent, mItemLayoutId, position);            convert(viewHolder,mData[position]);            System.Diagnostics.Debug.Write(position);            return viewHolder.GetConvertView();        }        public abstract void convert(ViewHolder helper, T item);        public ViewHolder GetViewHolder(int position, View convertView, ViewGroup parent)        {            return ViewHolder.Get(mContext, convertView, parent, mItemLayoutId, position);        }    }

写一个newsAdapter继承CommonAdapter，只需要将赋值的代码写在重写方法convert里面极客，这样就简化了很多的代码

    public class NewsAdapter<T> : CommonAdapter<T>    {        public NewsAdapter(Context context, List<T> data, int resId) : base(context, data, resId)        {        }        public override void convert(ViewHolder helper, T item)        {            NewsViewModel model = (NewsViewModel)Convert.ChangeType(item, typeof(NewsViewModel));            helper.SetText(Resource.Id.tv_news_title, model.Title);            helper.SetText(Resource.Id.tv_news_id, model.NewsID.ToString());            helper.SetText(Resource.Id.tv_news_desc, model.Desc);        }    }

C#委托和Java匿名内部类的比较

看来上面的例子，虽然简化了很多代码，但是每个ListView还是得新建一个Adapter，看来hongyang大神的博客在java中用匿名内部类实现一个Adapter万能通用，但是c#中没有匿名内部内的概念，这就尴尬了。。。。。
c#中虽然没有这种概念，但语言是相通的，但是委托可以实现。万能通用的adapter代码如下：

    public class Common1Adapter<T> : BaseAdapter    {        Context mContext;        List<T> mData;        int mItemLayoutId;        public delegate View GetViewEvent(int position, View convertView, ViewGroup parent, T item, ViewHolder viewHolder);        public event GetViewEvent OnGetView;        public Common1Adapter(Context context, List<T> data, int itemLayoutId) : base()        {            this.mContext = context;            mData = data;            mItemLayoutId = itemLayoutId;        }        public override int Count        {            get            {                return mData.Count;            }        }        public override Java.Lang.Object GetItem(int position)        {            return null;        }        public override long GetItemId(int position)        {            return position;        }        public override View GetView(int position, View convertView, ViewGroup parent)        {            var item = mData[position];            ViewHolder viewHolder = ViewHolder.Get(mContext, convertView, parent, mItemLayoutId, position);            if (OnGetView != null)                return this.OnGetView(position,convertView,parent,item,viewHolder);            return convertView;        }    }}

在使用时，只需要在Activity中注册OnGetView 事件，这样多个ListView的Adapter就只需要一个通用的Adapter就行了

   View OnGetView(int position,View  convertView,ViewGroup parent,NewsViewModel model,ViewHolder viewHolder)        {            viewHolder.SetText(Resource.Id.tv_news_title, model.Title);            viewHolder.SetText(Resource.Id.tv_news_id, model.NewsID.ToString());            viewHolder.SetText(Resource.Id.tv_news_desc, model.Desc);            return viewHolder.GetConvertView();        }   List<NewsViewModel> list_news = new List<Adaptes.NewsViewModel>() {                new Adaptes.NewsViewModel () { NewsID =1,Title="测试标题124578cdascdas",Desc ="测acdsdas试内内容10c2da4s内容10c2da4s内容10c2da4s容10c2da4sc5das4cdas"},                new Adaptes.NewsViewModel () { NewsID =2,Title="cascascda24578cdascdas",Desc ="测dasc试内容10c2da4s内容10c2da4s内容10c2da4s内容10c2da4sc5das4cdas"},            };            Common1Adapter<NewsViewModel> adapter = new Adaptes.Common1Adapter<Adaptes.NewsViewModel>(this, list_news, Resource.Layout.item_listview_news);            adapter.OnGetView += OnGetView;            lv_news.Adapter = adapter;

作者：张林
标题：xamarin android 打造ListView万能适配器
原文地址：http://blog.csdn.net/kebi007/article/details/77101947
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