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How to: Pass Values Between ASP.NET Web Pages

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If your application redirects (navigates) from one ASP.NET Web page to another, you will frequently want to pass information from the source page to the target page. For example, you might have a page where users can select items to purchase. When users submit the page, you want to call another page that can process the information that the user has entered.

You can pass information between pages in various ways, some of which depend on how the redirection occurs. Options include the following:

  • Use a query string, which appends information onto the URL of the target page. You can use a query string when using a HyperLink control to build navigation into a page or when you are programmatically redirecting to another page using the Redirect method.

    Passing values in a query string works even if the pages are not in the same Web application; it also works if you want to pass information to a page that is not an ASP.NET Web page. If the target page is an ASP.NET Web page, you can read the value of the query string out of the QueryString property of the HttpRequest object.

    NoteNote

    Never pass sensitive data using a query string, because the information is visible to users and can easily be modified, thus representing a potential security risk.

  • Use session state to store information that is then accessible to all ASP.NET Web pages in the current application. However, this takes server memory, and the information is stored until the session expires, which can be more overhead than you want for simply passing information to the next page. For details, see ASP.NET State Management Overview.

  • On the target page, read control values and public property values directly out of the source page. This strategy works in two situations: when the source page cross-posts to the target page (for more information, see How to: Post ASP.NET Web Pages to a Different Page), and when you call the Transfer method to transfer execution from the source to the target page on the server. The strategy of reading values directly from the source page is described in this topic.

Getting Public Property Values from the Source Page

If you are designing the source page specifically for sharing information with target pages, and both pages are ASP.NET Web pages, in the source page you can add public properties that expose information you want to share between pages. You can then read the values of the properties in the target pages.

NoteNote

You can read source page properties in the target page only if both pages are in the same Web application.

To get public property values from the source page

  1. On the source page, create one or more public properties.

    The following code example shows a property named CurrentCity that exposes the value of a TextBox control named textCity.

    Public ReadOnly Property CurrentCity() As String
    Get
        Return textCity.Text
    End Get
End Property

    public String CurrentCity
{
    get
    {
        return textCity.Text;
    }
}
    NoteNote

    Properties on the source page that are created primarily to expose values for cross-page posting are usually read-only properties. Although the source page can contain public read/write properties, setting a source page property from the target page property generally has no purpose, because the value will not be persisted.

  2. On the target page, add an @ PreviousPageType page directive that points to the source page.

    The following code example shows a PreviousPageType directive that references a source page named SourcePage.aspx.

    <%@ PreviousPageType VirtualPath="~/SourcePage.aspx" %>

    The PreviousPageType directive causes the page's PreviousPage property to be typed to the source page class.

  3. In target page code, use strongly typed members of the PreviousPage property to read the source code properties.

    The following code example reads the value of the CurrentCity property that is defined in the source page.

    Label1.Text = PreviousPage.CurrentCity

    Label1.Text = PreviousPage.CurrentCity;

Getting Control Information from the Source Page in the Same Application

If the source and target pages are both ASP.NET Web pages and in the same Web application, you can read the values of controls on the source page while in the target page. You might use this strategy if the source page does not expose public properties containing the information you need.

To get the values of controls from the source page in the same application

  • On the target page, get a reference to the source page by using the target page's PreviousPage property, and then call the FindControl method to get a reference to the control you want.

    The following code example gets the value of the source page's TextBox1 control and displays it in the control named Label1:

    If Not Page.PreviousPage Is Nothing Then
    Dim SourceTextBox As TextBox
    SourceTextBox = CType(PreviousPage.FindControl("TextBox1"), _
        TextBox)
    If Not SourceTextBox Is Nothing Then
        Label1.Text = SourceTextBox.Text
    End If
End If

    if (Page.PreviousPage != null)
{
    TextBox SourceTextBox = 
        (TextBox)Page.PreviousPage.FindControl("TextBox1");
    if (SourceTextBox != null)
    {
        Label1.Text = SourceTextBox.Text;
    }
}
    NoteNote

    The FindControl method finds controls in the current naming container. If the control you are looking for is inside another control (typically, inside a template), you must first get a reference to the container, and then search the container to find the control that you want to get.

Getting Post Information from the Source Page in Another Application

If the source and target pages are not in the same Web application, you can read the posted values of the source page in the target page. This technique also works if the target page is an ASP.NET Web page but the source page is not. Note that you can get only the post values; you cannot read the values of arbitrary controls on the page.

To get the values of controls from the source page in another application

  • On the target page, read the Form collection, which returns a dictionary of name/value pairs, one pair for each posted value.

    The following code example displays the ID and value of every posted control in the source page and displays the posted values in a label named Label1.

    NoteNote

    Post information from an ASP.NET Web pages includes the values of hidden fields, such as __VIEWSTATE, __EVENTTARGET, and __EVENTARGUMENT, which are used for internal processing in the page. The following code example excludes the values of posted fields that are named with a leading double underscore (__).

    		 
    Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
        Handles Me.Load
    Dim displayValues As New StringBuilder()
    Dim postedValues As NameValueCollection = Request.Form
    Dim nextKey As String
    For i As Integer = 0 To postedValues.AllKeys.Length - 1
        nextKey = postedValues.AllKeys(i)
        If nextKey.Substring(0, 2) <> "__" Then
            displayValues.Append("<br>")
            displayValues.Append(nextKey)
            displayValues.Append(" = ")
            displayValues.Append(postedValues(i))
        End If
    Next
    Label1.Text = displayValues.ToString()
End Sub

    void Page_Load(object sender, EventArgs e)
{
    System.Text.StringBuilder displayValues = 
        new System.Text.StringBuilder();
    System.Collections.Specialized.NameValueCollection 
        postedValues = Request.Form;
    String nextKey;
    for(int i = 0; i < postedValues.AllKeys.Length - 1; i++)
    {
        nextKey = postedValues.AllKeys[i];
        if(nextKey.Substring(0, 2) != "__")
        {
            displayValues.Append("<br>");
            displayValues.Append(nextKey);
            displayValues.Append(" = ");
            displayValues.Append(postedValues[i]);
        }
    }
   Label1.Text = displayValues.ToString();
}

See Also

Tasks

How to: Determine How ASP.NET Web Pages Were Invoked

Concepts

Cross-Page Posting in ASP.NET Web Pages
ASP.NET State Management Overview