小编给大家分享一下xamarin Android如何实现ListView万能适配器，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
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 Views;
View ConvertView;
private Context context ;
int mPosition;
private ViewHolder(Context _context,ViewGroup parent ,int itemLayoutId,int position)
{
this.mPosition = position;
Views = new SparseArray();
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(int viewId) where T :View
{
View view = Views.Get(viewId);
if (view == null)
{
view = ConvertView.FindViewById(viewId);
Views.Put(viewId,view);
}
return (T)view;
}
public View GetConvertView()
{
return ConvertView;
}
///
/// 给TextView 设置文本
///
///
///
/// (viewId);
view.Text = text;
return this;
}
///
/// 给ImageView 设置图片
///
public ViewHolder SetImageBitMap(int viewId , Bitmap bm)
{
ImageView view = GetView(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:BaseAdapter { Context mContext; List mData; int mItemLayoutId; public CommonAdapter(Context context, List 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: CommonAdapter { public NewsAdapter(Context context, List 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: BaseAdapter { Context mContext; List 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 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 list_news = new List() {
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 adapter = new Adaptes.Common1Adapter(this, list_news, Resource.Layout.item_listview_news);
adapter.OnGetView += OnGetView;
lv_news.Adapter = adapter; 以上是“xamarin Android如何实现ListView万能适配器”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注创新互联行业资讯频道！