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PostBackTrigger Class

  • Reference

Definition

Namespace:
System.Web.UI
Assembly:
System.Web.Extensions.dll

Defines a control inside a UpdatePanel control as a postback control.

C# 
public class PostBackTrigger : System.Web.UI.UpdatePanelControlTrigger
Inheritance
Object
UpdatePanelTrigger
UpdatePanelControlTrigger
PostBackTrigger

Examples

The following example shows how to declaratively define a PostBackTrigger 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 PostBackTrigger, because files cannot be uploaded asynchronously.

ASP.NET (C#) 
<%@ 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">

    private string saveDir = @"Uploads\";
    
    protected void UploadButton_Click(object sender, EventArgs e)
    {
        if (FileUpload1.HasFile && FileUpload1.FileBytes.Length < 10000 &&
            !CheckForFileName())
        {
            string savePath = 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.";
        }
    }

    protected void CheckButton_Click(object sender, EventArgs e)
    {
        if (FileName.Text.Length > 0)
        {
            string s = CheckForFileName() ? "exists already." : "does not exist.";
            UploadStatusLabel.Text = "The file name choosen " + s;
        }
        else
        {
            UploadStatusLabel.Text = "Specify a file name to check.";
        }
    }
    private Boolean CheckForFileName()
    {
        System.IO.FileInfo fi = new System.IO.FileInfo(Request.PhysicalApplicationPath + 
            saveDir + Server.HtmlEncode(FileName.Text));
            return fi.Exists;
    }

</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>

Remarks

Use the PostBackTrigger 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.

Not

Programmatically adding PostBackTrigger controls is not supported.

If a control is set as both a PostBackTrigger and AsyncPostBackTrigger control, an exception is thrown.

Constructors

PostBackTrigger()

Initializes a new instance of the PostBackTrigger class.

Properties

ControlID

Gets or sets the name of the control that is an PostBackTrigger control for an UpdatePanel control.
Owner

Gets a reference to the UpdatePanel control that the UpdatePanelTrigger targets.

(Inherited from UpdatePanelTrigger)

Methods

Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
FindTargetControl(Boolean)

Searches for the control specified in the ControlID property.

(Inherited from UpdatePanelControlTrigger)
GetHashCode()

Serves as the default hash function.

(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.
Initialize()

Initializes the PostBackTrigger object.
MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
ToString()

Returns a string that represents the current PostBackTrigger object.

Applies to

Ürün Sürümler
.NET Framework 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1

See also