Set TextBox Text to special value from Mater Page class

Question

So I have Web Forms project in Visual Studio with Master page. It the Add.aspx I have:

<div class="form-group">
    <asp:textBox runat="server" ID="surname" CssClass="textbox"></asp:textBox>
    <label for="surname">Surname</label>
</div>

I want to set text in this TextBox from Master Page. In Add.aspx.cs I have:

protected void Page_Load(object sender, EventArgs e)
{
}
public void SetSurname(String value)
{
    this.surname.Text = value;
}

And at Site.Master.cs I am trying to call SetSurname to set it to special value:

protected void Page_Load(object sender, EventArgs e)
{
    Add AddForm = new Add();
    AddForm.SetSurname("Test");
}

But I am getting error: Object reference does not point to an instance of an object pointing to this.surname.Text = value;. Am I wrong somewhere? Mabye I should use some functions like Page_Afterload or etc.

Answer 1

If i understant correctly, the TextBox surename exists only in Add.aspx. If so, you won't be able to call the method SetSurname() from anywhere else except inside of Add.aspx, because there is no guarantee the the Control surename exists in the current showing page. Also, the line Add AddForm = new Add(); is meaningless, unless you use it somewhere else in the code. If you want to use SetSurname(), you should do that from the Page_Load() of Add.aspx.

If I got the wohle thing wrong please notify me.