WindowsForm实现TextBox占位符Placeholder提示功能

public class ZhmTextBox: TextBox
{
 private const int EM_SETCUEBANNER = 0x1501;

 [DllImport("user32.dll", CharSet = CharSet.Auto)]
 private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)]string lParam);

 private string placeholder = string.Empty;
 public string Placeholder
 {
 get { return placeholder; }
 set
 {
  placeholder = value;
  SendMessage(Handle, EM_SETCUEBANNER, 0, Placeholder);
 }
 }
}

private void Form1_Load(object sender, EventArgs e)
{
 textBox1.Text = "此处是一些提示内容...";
 textBox1.LostFocus += TextBox1_LostFocus;
 textBox1.GotFocus += TextBox1_GotFocus;
}

private void TextBox1_GotFocus(object sender, EventArgs e)
{
 textBox1.Text = "";
}

private void TextBox1_LostFocus(object sender, EventArgs e)
{
 if (string.IsNullOrWhiteSpace(textBox1.Text))
 textBox1.Text = "此处是一些提示内容...";
}