YouTip

## ASP.NET LinkButton PostBackUrl Property The `PostBackUrl` property of the `LinkButton` control is a powerful feature in ASP.NET Web Forms. It allows developers to perform **cross-page posting**, redirecting the user and submitting the form data to a different target page instead of posting back to the same page. --- ## Definition and Usage By default, when a user clicks a `LinkButton` control, the page posts back to itself (self-postback). The `PostBackUrl` property gets or sets the URL of the target page to which you want to post the form data when the `LinkButton` control is clicked. This is highly useful for multi-step wizards, search result redirection, or passing form inputs directly to another processing page. --- ## Syntax ```xml ``` ### Property Values | Value | Description | | :--- | :--- | | `string` | A string representing the URL of the target page for the postback. The default is an empty string (`""`), which causes the page to post back to itself. | --- ## Code Example The following example demonstrates how to set the `PostBackUrl` property of a `LinkButton` control to submit user input to a target page named `TargetPage.aspx`. ### Source Page (`SourcePage.aspx`) ```xml <%@ Page Language="C#" %>

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``` ### Target Page (`TargetPage.aspx.cs`) To retrieve the values submitted from the source page, you can use the `PreviousPage` property in the code-behind of the target page: ```csharp using System; using System.Web.UI; using System.Web.UI.WebControls; public partial class TargetPage : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { // Check if the page was loaded via a cross-page postback if (PreviousPage != null && PreviousPage.IsCrossPagePostBack) { // Find the TextBox control from the source page TextBox txtName = (TextBox)PreviousPage.FindControl("TextBox1"); if (txtName != null) { Response.Write("Hello, " + Server.HtmlEncode(txtName.Text) + "! Welcome to the target page."); } } else { Response.Write("This page was not accessed via a cross-page postback."); } } } ``` --- ## Key Considerations & Best Practices 1. **Cross-Page Postback Detection**: Always check `PreviousPage != null` and `PreviousPage.IsCrossPagePostBack` in the target page before attempting to access controls from the source page to prevent `NullReferenceException` errors. 2. **Control Access**: Use `PreviousPage.FindControl("ControlID")` to access controls from the source page. If you want strongly-typed access to the source page's properties, add the `@PreviousPageType` directive to the target `.aspx` page: ```xml <%@ PreviousPageType VirtualPath="~/SourcePage.aspx" %> ``` 3. **Validation**: If the source page contains ASP.NET validation controls (like `RequiredFieldValidator`), the cross-page postback will only occur if the source page validation passes (unless `CausesValidation="false"` is set on the `LinkButton`). 4. **Client-Side Behavior**: Under the hood, ASP.NET injects client-side JavaScript (`WebForm_DoPostBackWithOptions`) to modify the form's action attribute dynamically before submission when a `PostBackUrl` is specified. Ensure JavaScript is enabled in the client browser for this feature to work correctly.