System.NullReferenceException - access iframe by Id

Question

User-909867351 posted

Hi I want to access one iframe ane put his src to a youtube video. Here is my code:

 protected void Mostra_Filme(object sender, EventArgs e)
    {
        ImageButton btn = sender as ImageButton;
        //Get the listviewitem from button
        RepeaterItem item = (RepeaterItem)(sender as Control).NamingContainer;
        //Find the label control
        Label filme = (Label)item.FindControl("video");
        HtmlControl frame1 = (HtmlControl)this.FindControl("Iframe1");
        frame1.Attributes["src"] = "https://www.youtube.com/watch?v=w1-LoH0iKWU";
        ScriptManager.RegisterStartupScript(this, this.GetType(), "Pop", "openModal();", true);
    }

and aspx file

<div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
        <div class="modal-dialog modal-lg" role="document">
            <div class="modal-content">
                <div class="modal-header">
                    <h5 class="modal-title" id="exampleModalLabel">Filme Promocional</h5>
                    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                        <span aria-hidden="true">&times;</span>
                    </button>
                </div>
                <div class="modal-body">
                    <div class="row justify-content-center">
                        <div class="col-md-10 ">
                            <iframe  width="560" height="315"  id="Iframe1"  frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
                        </div>                                               
                    </div>                                              
                </div>            
      <div class="modal-footer">        
          <asp:Button ID="Button2" CssClass="btn btn-primary" runat="server" Text="Confirmar"  />
          <br />                  
      </div>
    </div>
  </div>
</div>

Why do I get this error?

Thank you