Doubt about Containsignorecase in a textbox

Question

The problem is in the following description :

CS1061 error

"string" does not contain a definition for "Containsignorecase" and was not can find no method of extension "Containsignorecase" that accept a first "string" argument (there is a usage directive or missing Assembly reference?)

I created an Extension there at the beginning in a public Static, but it didn’t help.. What else can I do?

Error happens in [Step 2.1]

namespace MyMethod 
{
    public static class MyExtensions 
    {
        public static bool ContainsIgnoreCase(this string source, string search)
        {

           return source.IndexOf(search, StringComparison.CurrentCultureIgnoreCase) >= 0;

        }   
    }    
}

Use

private void txtBuscarJogo_TextChanged(object sender, EventArgs 
{
    var controles = _todosBotoes.Where(btnArcheAge => (btnArcheAge.Tag as String ??    btnArcheAge.Text).ContainsIgnoreCase(txtBuscarJogo.Text)).ToArray();
    //Passo 2.2
    mainPanel.Controls.Clear();
    //Passo 2.3
    mainPanel.Controls.AddRange(controles);
}

Answer 1

All that remains is to include the namespace in the class of Form. In fact, the name of namespace is not good, try to put something more descriptive, as MyExtensionsMethods.

// Outros using
using MyMethod;

namespace SeuNamespace
{
    public partial class Form1 { }
}