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 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;
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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