Defines a control inside a UpdatePanel control as a postback control.
Assembly: System.Web.Extensions (in System.Web.Extensions.dll)
Thetype exposes the following members.
|Equals(Object)||Determines whether the specified object is equal to the current object. (Inherited from Object.)|
|Finalize||Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)|
|FindTargetControl||Searches for the control specified in the ControlID property. (Inherited from UpdatePanelControlTrigger.)|
|GetHashCode||Serves as a hash function for a particular type. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|HasTriggered||Returns a value that indicates whether the trigger was activated. (Overrides UpdatePanelTrigger.HasTriggered.)|
|Initialize||Initializes the object. (Overrides UpdatePanelTrigger.Initialize.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|ToString||Returns a string that represents the current object. (Overrides Object.ToString.)|
Use the control to enable controls inside an UpdatePanel to cause a postback instead of performing an asynchronous postback.
Use the RegisterPostBackControl method of the ScriptManager control to programmatically register a postback control. You can then call the Update method of the UpdatePanel control when the trigger control performs a postback.
Programmatically adding controls is not supported.
If a control is set as both a and AsyncPostBackTrigger control, an exception is thrown.
The following example shows how to declaratively define a control for an UpdatePanel control. In the panel, a FileUpload control enables users to upload a file. Users must first check whether the file to upload exists. The Button control that calls the event handler to check the file name causes an asynchronous postback. However, the Button control that uploads the file is registered as a , because files cannot be uploaded asynchronously.
<%@ 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"> Private saveDir As String = "Uploads\\" Protected Sub UploadButton_Click(ByVal sender As Object, ByVal e As EventArgs) If (FileUpload1.HasFile AndAlso FileUpload1.FileBytes.Length < 10000 AndAlso _ Not (CheckForFileName())) Then Dim savePath As String = Request.PhysicalApplicationPath & saveDir & _ Server.HtmlEncode(FileName.Text) 'Remove comment from the next line to upload file. 'FileUpload1.SaveAs(savePath) UploadStatusLabel.Text = "The file was processed successfully." Else UploadStatusLabel.Text = "You did not specify a file to upload, or a file name, or the file was too large. Please try again." End If End Sub Protected Sub CheckButton_Click(ByVal sender As Object, ByVal e As EventArgs) If (FileName.Text.Length > 0) Then Dim s As String If (CheckForFileName()) Then s = "exists already." Else s = "does not exist." End If UploadStatusLabel.Text = "The file name choosen " & s Else UploadStatusLabel.Text = "Specify a file name to check." End If End Sub Private Function CheckForFileName() As Boolean Dim fi As New System.IO.FileInfo(Request.PhysicalApplicationPath & _ saveDir & Server.HtmlEncode(FileName.Text)) Return fi.Exists End Function </script> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title>PostBackTrigger Example</title> </head> <body> <form id="form1" runat="server"> <div> <asp:ScriptManager ID="ScriptManager1" runat="server" /> The upload button is defined as a PostBackTrigger.<br/> <asp:UpdatePanel ID="UpdatePanel1" UpdateMode="Conditional" runat="server"> <ContentTemplate> <fieldset> <legend>FileUpload in an UpdatePanel</legend> First, enter a file name to upload your file to: <asp:TextBox ID="FileName" runat="server" /> <asp:Button ID="CheckButton" Text="Check" runat="server" OnClick="CheckButton_Click" /> <br /> Then, browse and find the file to upload: <asp:FileUpload id="FileUpload1" runat="server"> </asp:FileUpload> <br /> <asp:Button id="UploadButton" Text="Upload file" OnClick="UploadButton_Click" runat="server"> </asp:Button> <br /> <asp:Label id="UploadStatusLabel" runat="server" style="color:red;"> </asp:Label> </fieldset> </ContentTemplate> <Triggers> <asp:PostBackTrigger ControlID="UploadButton" /> </Triggers> </asp:UpdatePanel> </div> </form> </body> </html>