詳解xamarin Android 實現ListView萬能適配器
早些時候接觸xamarin Android 的列表，寫了很多ListView的Adapter，建一個ListView就寫一個Adapter,每一個Adapter里面還有去寫一個ViewHolder的類來優化，自從看了hongyang博客的listview萬能適配器的文章，學習良多，所以就寫篇關于xamarin android ListView通用適配器的文章。
本章主要分為以下三點：
打造通用的ViewHolder優化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> /// 給TextView 設置文本 /// </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> /// 給ImageView 設置圖片 /// </summary> public ViewHolder SetImageBitMap(int viewId , Bitmap bm) { ImageView view = GetView<ImageView>(viewId); view.SetImageBitmap(bm); return this; } }稍微解釋一下：
ViewHolder的構造方法中初始化變量，并將ListView的布局view的Tag設置成viewholder的實例
Get方法使用單例模式初始化ViewHolder
GetView泛型方法獲取ListView布局中的空間
SetText、SetImageBitMap給一些常用的控件復值
使用泛型Adapter適應不同布局的ListView
CommonAdapter是一個泛型的基類，一些重復的重寫方法都在這個基類，然后我們寫一個子類繼承這個CommonAdapter，就簡化了很多代碼
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); } }寫一個newsAdapter繼承CommonAdapter，只需要將賦值的代碼寫在重寫方法convert里面極客，這樣就簡化了很多的代碼
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匿名內部類的比較
看來上面的例子，雖然簡化了很多代碼，但是每個ListView還是得新建一個Adapter，看來hongyang大神的博客在java中用匿名內部類實現一個Adapter萬能通用，但是c#中沒有匿名內部內的概念，這就尷尬了。。。。。
c#中雖然沒有這種概念，但語言是相通的，但是委托可以實現。萬能通用的adapter代碼如下：
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; } }}在使用時，只需要在Activity中注冊OnGetView 事件，這樣多個ListView的Adapter就只需要一個通用的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="測試標題124578cdascdas",Desc ="測acdsdas試內內容10c2da4s內容10c2da4s內容10c2da4s容10c2da4sc5das4cdas"}, new Adaptes.NewsViewModel () { NewsID =2,Title="cascascda24578cdascdas",Desc ="測dasc試內容10c2da4s內容10c2da4s內容10c2da4s內容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 萬能適配器的實例，如有疑問請留言或者到本站社區交流討論，感謝閱讀，希望能幫助到大家，謝謝大家對本站的支持！
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