详解xamarin Android 实现ListView万能适配器
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
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;以上就是Android listview 万能适配器的实例，如有疑问请留言或者到本站社区交流讨论，感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！
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