ObjectDataSourceDisposingEventArgs.ObjectInstance 属性
定义
重要
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获取一个对象，该对象表示 ObjectDataSource 控件用来执行数据操作的业务对象。
public:
property System::Object ^ ObjectInstance { System::Object ^ get(); };public object ObjectInstance { get; }member this.ObjectInstance : objPublic ReadOnly Property ObjectInstance As Object属性值
ObjectDataSource 用来执行数据操作的业务对象；否则，如果将 null 传递给 ObjectDataSourceEventArgs，则为 null。
示例
下面的代码示例演示如何将 ObjectDataSource 控件与业务对象和控件配合使用 GridView 来显示信息。 你可能使用非常昂贵的业务对象， () 为网页执行的每个数据操作创建的时间或资源。 使用昂贵对象的一种方法可能是创建一次它的实例，然后缓存它以供后续操作，而不是为每个数据操作创建和销毁它。 此示例演示了此模式。 可以处理 ObjectCreating 事件以先检查对象的缓存，然后创建一个实例，前提是尚未缓存一个实例。 然后，处理 ObjectDisposing 事件以缓存业务对象以供将来使用，而不是销毁它。 在此示例中， CancelEventArgs.Cancel 类的 ObjectDataSourceDisposingEventArgs 属性设置为 true，以指示 ObjectDataSource 不对实例调用 Dispose 。
<%@ Import namespace="Samples.AspNet.CS" %>
<%@ Page language="c#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
// Instead of creating and destroying the business object each time, the
// business object is cached in the ASP.NET Cache.
private void GetEmployeeLogic(object sender, ObjectDataSourceEventArgs e)
{
// First check to see if an instance of this object already exists in the Cache.
EmployeeLogic cachedLogic;
cachedLogic = Cache["ExpensiveEmployeeLogicObject"] as EmployeeLogic;
if (null == cachedLogic) {
cachedLogic = new EmployeeLogic();
}
e.ObjectInstance = cachedLogic;
}
private void ReturnEmployeeLogic(object sender, ObjectDataSourceDisposingEventArgs e)
{
// Get the instance of the business object that the ObjectDataSource is working with.
EmployeeLogic cachedLogic = e.ObjectInstance as EmployeeLogic;
// Test to determine whether the object already exists in the cache.
EmployeeLogic temp = Cache["ExpensiveEmployeeLogicObject"] as EmployeeLogic;
if (null == temp) {
// If it does not yet exist in the Cache, add it.
Cache.Insert("ExpensiveEmployeeLogicObject", cachedLogic);
}
// Cancel the event, so that the object will
// not be Disposed if it implements IDisposable.
e.Cancel = true;
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>ObjectDataSource - C# Example</title>
</head>
<body>
<form id="Form1" method="post" runat="server">
<asp:gridview
id="GridView1"
runat="server"
datasourceid="ObjectDataSource1">
</asp:gridview>
<asp:objectdatasource
id="ObjectDataSource1"
runat="server"
selectmethod="GetCreateTime"
typename="Samples.AspNet.CS.EmployeeLogic"
onobjectcreating="GetEmployeeLogic"
onobjectdisposing="ReturnEmployeeLogic" >
</asp:objectdatasource>
</form>
</body>
</html>
<%@ Import namespace="Samples.AspNet.VB" %>
<%@ Page language="vb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
' Instead of creating and destroying the business object each time, the
' business object is cached in the ASP.NET Cache.
Sub GetEmployeeLogic(sender As Object, e As ObjectDataSourceEventArgs)
' First check to see if an instance of this object already exists in the Cache.
Dim cachedLogic As EmployeeLogic
cachedLogic = CType( Cache("ExpensiveEmployeeLogicObject"), EmployeeLogic)
If (cachedLogic Is Nothing) Then
cachedLogic = New EmployeeLogic
End If
e.ObjectInstance = cachedLogic
End Sub ' GetEmployeeLogic
Sub ReturnEmployeeLogic(sender As Object, e As ObjectDataSourceDisposingEventArgs)
' Get the instance of the business object that the ObjectDataSource is working with.
Dim cachedLogic As EmployeeLogic
cachedLogic = CType( e.ObjectInstance, EmployeeLogic)
' Test to determine whether the object already exists in the cache.
Dim temp As EmployeeLogic
temp = CType( Cache("ExpensiveEmployeeLogicObject"), EmployeeLogic)
If (temp Is Nothing) Then
' If it does not yet exist in the Cache, add it.
Cache.Insert("ExpensiveEmployeeLogicObject", cachedLogic)
End If
' Cancel the event, so that the object will
' not be Disposed if it implements IDisposable.
e.Cancel = True
End Sub ' ReturnEmployeeLogic
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>ObjectDataSource - VB Example</title>
</head>
<body>
<form id="Form1" method="post" runat="server">
<asp:gridview
id="GridView1"
runat="server"
datasourceid="ObjectDataSource1">
</asp:gridview>
<asp:objectdatasource
id="ObjectDataSource1"
runat="server"
selectmethod="GetCreateTime"
typename="Samples.AspNet.VB.EmployeeLogic"
onobjectcreating="GetEmployeeLogic"
onobjectdisposing="ReturnEmployeeLogic" >
</asp:objectdatasource>
</form>
</body>
</html>
注解
如果 (SelectMethod、 UpdateMethod、 DeleteMethod和 InsertMethod) 的数据操作方法是实例方法，则会在执行方法之前创建业务对象的实例。 通过将 对象保存在事件处理程序中的 属性ObjectDisposing中ObjectInstance，可以防止为每个调用创建业务对象。 在后续 ObjectCreating 事件中，可以从 属性中检索业务对象 ObjectInstance 。
