TextBox不会触发Invalidated事件

Question

为什么TextBox在插入符号出现和消失以及文本被更改时不会引发无效事件？

class Form1
{
    TextBox t = new TextBox();

    public Form1()
    {
        t.Invalidated += delegate(object sender,InvalidatedEventArgs e)
        {
            //this event doesn't be fired,why ?
        };
    }
}