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
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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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