通过

ObjectDataSourceDisposingEventArgs.ObjectInstance 属性

  • 参考

定义

命名空间:
System.Web.UI.WebControls
程序集:
System.Web.dll

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 : obj
Public ReadOnly Property ObjectInstance As Object

属性值

Object

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 。

适用于

另请参阅