ASP.NET ViewState 初探 (2) 轉自msdn
2024-07-10 12:58:32
供稿：網友
請看下面的示例：要在 web 頁上顯示一個項目列表，而每個用戶需要不同的列表排序。項目列表是靜態的，因此可以將這些頁面綁定到相同的緩存數據集，而排序順序只是用戶特定的 ui 狀態的一小部分。viewstate 非常適合于存儲這種類型的值。代碼如下：
[visual basic]
<%@ import namespace="system.data" %>
<html>
<head>
<title>用于頁面 ui 狀態值的 viewstate/title>
</head>
<body>
<form runat="server">
<h3>
在 viewstate 中存儲非控件狀態
</h3>
<p>
此示例將一列靜態數據的當前排序順序存儲在 viewstate 中。<br>
單擊列標題中的鏈接，可按該字段排序數據。<br>
再次單擊該鏈接，將按相反順序排序。
<br><br><br>
<asp:datagrid id="datagrid1" runat="server"
onsortcommand="sortgrid" borderstyle="none" borderwidth="1px"
bordercolor="#cccccc" backcolor="white" cellpadding="5" allowsorting="true">
<headerstyle font-bold="true" forecolor="white"
backcolor="#006699">
</headerstyle>
</asp:datagrid>
</p>
</form>
</body>
</html>
<script runat="server">
' 在 viewstate 中跟蹤 sortfield 屬性
property sortfield() as string
get
dim o as object = viewstate("sortfield")
if o is nothing then
return string.empty
end if
return cstr(o)
end get
set(value as string)
if value = sortfield then
' 與當前排序文件相同，切換排序方向
sortascending = not sortascending
end if
viewstate("sortfield") = value
end set
end property
' 在 viewstate 中跟蹤 sortascending 屬性
property sortascending() as boolean
get
dim o as object = viewstate("sortascending")
if o is nothing then
return true
end if
return cbool(o)
end get
set(value as boolean)
viewstate("sortascending") = value
end set
end property
private sub page_load(sender as object, e as eventargs) handles mybase.load
if not page.ispostback then
bindgrid()
end if
end sub
sub bindgrid()
' 獲取數據
dim ds as new dataset()
ds.readxml(server.mappath("testdata.xml"))
dim dv as new dataview(ds.tables(0))
' 應用排序過濾器和方向
dv.sort = sortfield
if not sortascending then
dv.sort += " desc"
end if
' 綁定網格
datagrid1.datasource = dv
datagrid1.databind()
end sub
private sub sortgrid(sender as object, e as datagridsortcommandeventargs)
datagrid1.currentpageindex = 0
sortfield = e.sortexpression
bindgrid()
end sub
</script>
[c#]
<%@ page language="c#" %>
<%@ import namespace="system.data" %>
<html>
<head>
<title>用于頁面 ui 狀態值的 viewstate</title>
</head>
<body>
<form runat="server">
<h3>
在 viewstate 中存儲非控件狀態
</h3>
<p>
此示例將一列靜態數據的當前排序順序存儲在 viewstate 中。<br>
單擊列標題中的鏈接，可按該字段排序數據。<br>
再次單擊該鏈接，將按相反順序排序。
<br><br><br>
<asp:datagrid id="datagrid1" runat="server" onsortcommand="sortgrid"
borderstyle="none" borderwidth="1px" bordercolor="#cccccc"
backcolor="white" cellpadding="5" allowsorting="true">
<headerstyle font-bold="true" forecolor="white" backcolor="#006699">
</headerstyle>
</asp:datagrid>
</p>
</form>
</body>
</html>
<script runat="server">
// 在 viewstate 中跟蹤 sortfield 屬性
string sortfield {
get {
object o = viewstate["sortfield"];
if (o == null) {
return string.empty;
}
return (string)o;
}
set {
if (value == sortfield) {
// 與當前排序文件相同，切換排序方向
sortascending = !sortascending;
}
viewstate["sortfield"] = value;
}
}
// 在 viewstate 中跟蹤 sortascending 屬性
bool sortascending {
get {
object o = viewstate["sortascending"];
if (o == null) {
return true;
}
return (bool)o;
}
set {
viewstate["sortascending"] = value;
}
}
void page_load(object sender, eventargs e) {
if (!page.ispostback) {
bindgrid();
}
}
void bindgrid() {
// 獲取數據
dataset ds = new dataset();
ds.readxml(server.mappath("testdata.xml"));
dataview dv = new dataview(ds.tables[0]);
// 應用排序過濾器和方向
dv.sort = sortfield;
if (!sortascending) {
dv.sort += " desc";
}
// 綁定網格
datagrid1.datasource = dv;
datagrid1.databind();
}
void sortgrid(object sender, datagridsortcommandeventargs e) {
datagrid1.currentpageindex = 0;
sortfield = e.sortexpression;
bindgrid();
}
</script>
下面是上述兩個代碼段中引用的 testdata.xml 的代碼：
<?xml version="1.0" standalone="yes"?>
<newdataset>
<table>
<pub_id>0736</pub_id>
<pub_name>new moon books</pub_name>
<city>boston</city>
<state>ma</state>
<country>usa</country>
</table>
<table>
<pub_id>0877</pub_id>
<pub_name>binnet & hardley</pub_name>
<city>washington</city>
<state>dc</state>
<country>usa</country>
</table>
<table>
<pub_id>1389</pub_id>
<pub_name>algodata infosystems</pub_name>
<city>berkeley</city>
<state>ca</state>
<country>usa</country>
</table>
<table>
<pub_id>1622</pub_id>
<pub_name>five lakes publishing</pub_name>
<city>chicago</city>
<state>il</state>
<country>usa</country>
</table>
<table>
<pub_id>1756</pub_id>
<pub_name>ramona publishers</pub_name>
<city>dallas</city>
<state>tx</state>
<country>usa</country>
</table>
<table>
<pub_id>9901</pub_id>
<pub_name>ggg&g</pub_name>
<city>muenchen</city>
<country>germany</country>
</table>
<table>
<pub_id>9952</pub_id>
<pub_name>scootney books</pub_name>
<city>new york</city>
<state>ny</state>
<country>usa</country>
</table>
<table>
<pub_id>9999</pub_id>
<pub_name>lucerne publishing</pub_name>
<city>paris</city>
<country>france</country>
</table>
</newdataset>
