C#如何让textBox中显示一些内容，然后鼠标单击进去之后自动清空？

public class TextBoxUi:TextBox { private const uint ECM_FIRST = 0x1500; private const uint EM_SETCUEBANNER = ECM_FIRST + 1; [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)] static extern IntP