C#笔记（5）textbox的hint属性

新建类

    public static class Win32Utility
    {

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

        [DllImport("user32.dll")]
        private static extern bool SendMessage(IntPtr hwnd, int msg, int wParam, StringBuilder lParam);

        [DllImport("user32.dll")]
        private static extern bool GetComboBoxInfo(IntPtr hwnd, ref COMBOBOXINFO pcbi);

        [StructLayout(LayoutKind.Sequential)]
        private struct COMBOBOXINFO
        {
            public int cbSize;
            public RECT rcItem;
            public RECT rcButton;
            public IntPtr stateButton;
            public IntPtr hwndCombo;
            public IntPtr hwndItem;
            public IntPtr hwndList;
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        private const int EM_SETCUEBANNER = 0x1501;
        private const int EM_GETCUEBANNER = 0x1502;

        public static void SetCueText(Control control, string text)
        {
            if (control is ComboBox)
            {
                COMBOBOXINFO info = GetComboBoxInfo(control);
                SendMessage(info.hwndItem, EM_SETCUEBANNER, 0, text);
            }
            else
            {
                SendMessage(control.Handle, EM_SETCUEBANNER, 0, text);
            }
        }

        private static COMBOBOXINFO GetComboBoxInfo(Control control)
        {
            COMBOBOXINFO info = new COMBOBOXINFO();
            //a combobox is made up of three controls, a button, a list and textbox; 
            //we want the textbox 
            info.cbSize = Marshal.SizeOf(info);
            GetComboBoxInfo(control.Handle, ref info);
            return info;
        }

        public static string GetCueText(Control control)
        {
            StringBuilder builder = new StringBuilder();
            if (control is ComboBox)
            {
                COMBOBOXINFO info = new COMBOBOXINFO();
                //a combobox is made up of two controls, a list and textbox; 
                //we want the textbox 
                info.cbSize = Marshal.SizeOf(info);
                GetComboBoxInfo(control.Handle, ref info);
                SendMessage(info.hwndItem, EM_GETCUEBANNER, 0, builder);
            }
            else
            {
                SendMessage(control.Handle, EM_GETCUEBANNER, 0, builder);
            }
            return builder.ToString();
        }

    }

2.使用

Win32Utility.SetCueText(textBox_username, "用户名");
Win32Utility.SetCueText(textBox_password, "密码");