[عيد مبارك]

كود :

Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim txt As TextBox = FindControls(Me, "TextBox1").FirstOrDefault
        If txt IsNot Nothing Then
            txt.Text = "123"
        End If
    End Sub


    Private Function FindControls(ByVal c As Control, ByVal n As String) As IEnumerable(Of Control)
        Dim cs = c.Controls.Cast(Of Control)()
        Return cs.SelectMany(Function(ctrl) FindControls(ctrl, n)).Concat(cs).Where(Function(x) x.Name.Equals(n))
    End Function


End Class