Pass master page control values on content page on page_load

I have a dropdowlist on master page and I want to pass the selected value on content pages when a content page loads. My problem is that the value passes only when I change value on the dropdownlist. So when a page load I have to reselect from dropdownlist to capture the value of the dropdown. If I am browsing the content pages the selected value doesnt pass on page load.
My master page code .net:

<asp:DropDownList ID="ddlcategories" 
        runat="server" DataSourceID="SqlDataSourcecategories" DataTextField="CategoryName" 
        DataValueField="CategoryID" AutoPostBack="True" 
        onselectedindexchanged="ddlcategories_SelectedIndexChanged"></asp:DropDownList>

Master page cs:

protected void Page_Load(object sender, EventArgs e)
{
 if (!IsPostBack)
 {    
      ddlcategories.DataBind();
      ddlcategories.Items.Insert(0, "Uncategorized");
      ddlcategories.Items[0].Value = "0";
      ddlcategories.SelectedValue = Convert.ToString(Session["lblCategoryID"]);
  }
}
protected void ddlcategories_SelectedIndexChanged(object sender, EventArgs e)
{
    Session["lblCategoryID"] = Convert.ToInt32(ddlcategories.SelectedValue);
}

Content page cs:

protected void Page_Load(object sender, EventArgs e)
{                
    Label10.Text = Convert.ToString(((DropDownList)Master.FindControl("ddlcategories")).SelectedValue);                 
}

Answers:

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Method 1

Try this solution:

Master page:

<asp:DropDownList ID="ddlcategories" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddlcategories_SelectedIndexChanged">
    <asp:ListItem>One</asp:ListItem>
    <asp:ListItem>Two</asp:ListItem>
</asp:DropDownList>

Master page CS:

public string SelectedValue
{
    get
    {
        return ddlcategories.SelectedValue;
    }
    set
    {
        ddlcategories.SelectedValue= value;
    }
}

protected void ddlcategories_SelectedIndexChanged(object sender, EventArgs e)
{
    SelectedValue = ddlcategories.SelectedValue;
}

Content Page markup:

<%@ MasterType VirtualPath="~/Site1.Master" %>

<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>

Content page CS.

protected void Page_PreRender(object sender, EventArgs e)
{
    Label1.Text = Master.SelectedValue;
}

Note: Values are just to demonstrate, you can use the actual data source values in drop down.

Method 2

Your issue is as the “ContentPage load” occurs before the “MasterPage load” you don’t have access to the dropdownlist items.

to solve this issue you can Bind your drobdownlist first in the master page , but not in the “MasterPage load” , you can Bind it in “MasterPage Init” event which occurs before the “ContentPage Init” and “MasterPage Load” events .

    protected void Page_Init(object sender, EventArgs e)
{  
      ddlcategories.DataBind();
      ddlcategories.Items.Insert(0, "Uncategorized");
      ddlcategories.Items[0].Value = "0";
      ddlcategories.SelectedValue = Convert.ToString(Session["lblCategoryID"]);
}

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0