查找当前页面或窗口中某类型控件并赋值

WinForm

foreach (Control control in this.Controls) {
    if (control is TextBox) {
        (control as TextBox).Text = "Hello World.";
    }
}

ASP.NET

foreach (Control control in this.FindControl("form1").Controls) {
    if (control is TextBox) {
        (control as TextBox).Text = "Hello world.";
    }
}