动态加载用户控件至DataList并为用户控件赋值实例演示

为了实现这个演示，insus.net使用通用的新闻例子，它类别(目录)以及文章。在一个页面，显示所有类别，每个目录下显示最新几条新闻。

效果如下：
目录是用datalist控件显示，而文章标题列表是一个用户控件显示，这个用户控件将动态被加入至datalist。

view code
<asp:repeater id="repeater1" runat="server" onitemdatabound="repeater1_itemdatabound">
<headertemplate>
<table cellpadding="5" cellspacing="0" width="100%">
</headertemplate>
<itemtemplate>
<tr style="height: 30px; line-height: 10px;">
<td>
$
</td>
<td>
<asp:hyperlink id="hyperlink1" runat="server" navigateurl='<%# "~/articleview.aspx?id=" & eval("article_nbr")%>' tooltip='<%# eval("subject")%>' target="_blank"></asp:hyperlink>
</td>
<td>
<%# objinsusdatetimeutility.getdatetime(eval("publicdate"), "yyyy-mm-dd")%>
</td>
</tr>
</itemtemplate>
<footertemplate>
</table>
</footertemplate>
</asp:repeater>

view code
view code
imports system.data
imports insus.net
partial class ascxcontrols_articlelist
inherits system.web.ui.usercontrol
implements isetvalue '继承接口
dim objarticle as new article()
protected objinsusdatetimeutility as new insusdatetimeutility()
private _datasource as object
private _subjectlength as integer = 20
public writeonly property subjectlength() as integer
set(byval value as integer)
_subjectlength = value
end set
end property
protected sub page_load(byval sender as object, byval e as eventargs) handles me.load
data_binding()
end sub
'绑定数据至repeater控件
private sub data_binding()
me.repeater1.datasource = _datasource
me.repeater1.databind()
end sub
protected sub repeater1_itemdatabound(byval sender as object, byval e as repeateritemeventargs)
dim objdrv as datarowview = directcast(e.item.dataitem, datarowview)
if e.item.itemtype = listitemtype.alternatingitem orelse e.item.itemtype = listitemtype.item then
if e.item.findcontrol("hyperlink1") isnot nothing then
dim linksubject as hyperlink = directcast(e.item.findcontrol("hyperlink1"), hyperlink)
if objdrv("subject").length > _subjectlength then
linksubject.text = objdrv("subject").substring(0, _subjectlength) & "..."
else
linksubject.text = objdrv("subject").tostring()
end if
end if
end if
end sub
'实现接口
public sub setvalue(str as object) implements isetvalue.setvalue
me._datasource = str
end sub
end class

上面用户控件中，有一个接口：

isetvalue
using system;
using system.collections.generic;
using system.linq;
using system.text;
namespace insus.net
{
public interface isetvalue
{
void setvalue(object obj);
}
}

显示目录：

view code
<asp:datalist id="datalistcatalog" runat="server" repeatcolumns="2" repeatdirection="horizontal" datakeyfield="catalog_nbr" onitemdatabound="datalistcatalog_itemdatabound">
<itemtemplate>
<div style="padding:2px; height:25px; background-color:#cbfb25; font-weight:bold; line-height:25px;">
<%# eval("catalogname")%>
</div>
<asp:placeholder id="placeholderarticlelist" runat="server"></asp:placeholder>
</itemtemplate>
</asp:datalist>

从数据库获取数据并绑定至目录的datalist控件。

view code
imports insus.net
partial class index
inherits system.web.ui.page
dim objcatalog as new catalog()
dim objarticle as new article()
protected sub page_load(sender as object, e as eventargs) handles me.load
if not ispostback then
data_binding()
end if
end sub
private sub data_binding()
objcatalog.isactive = true
me.datalistcatalog.datasource = objcatalog.getbyisactive()
me.datalistcatalog.databind()
end sub
end class

下面是重点，就是onitemdatabound事件，在这个事件中，需要找到asp:placeholder控件，这个容器将用来加载用户控件。

protected sub datalistcatalog_itemdatabound(sender as object, e as datalistitemeventargs)
if e.item.itemtype = listitemtype.item orelse e.item.itemtype = listitemtype.alternatingitem then
'判断asp:placeholder是否存在
if e.item.findcontrol("placeholderarticlelist") isnot nothing then
dim ctllaceholder as placeholder = directcast(e.item.findcontrol("placeholderarticlelist"), placeholder)
'动态加载用户控件，并转换为接口。
dim objuc as isetvalue = directcast(loadcontrol("~/ascxcontrols/articlelist.ascx"), isetvalue)
'找到datalist控件的目录主键
objarticle.catalog_nbr = me.datalistcatalog.datakeys(e.item.itemindex)
objarticle.top = 2
'为用户控件赋值。
objuc.setvalue(objarticle.getarticaltopbycatalog())
'加载用户控件。
ctllaceholder.controls.add(objuc)
end if
end if
end sub