如何在C＃winforms中将背景图像放置到DateTimePicker？

Question

I am trying to create some user controls.

And also trying to notify that the control must be selected or written with user input.

So, my idea is to draw image on the right-top corner of the control.

I have successfully done with TextBox control.

But for the DateTimePicker control, I have no idea where to start with.

Here is my code below:

public partial class DateTimePicker : System.Windows.Forms.DateTimePicker
{
    public DateTimePicker()
    {
        InitializeComponent();

    }

    protected override void OnLayout(LayoutEventArgs levent)
    {
        base.OnLayout(levent);


        Bitmap bmp  = new Bitmap(Assembly.GetExecutingAssembly().GetManifestResourceStream("MyControls.Resources.Images.required01.gif"));
        this.Parent.CreateGraphics().DrawImage(bmp, 10, 10);
    }
}

this.Parent.CreateGraphics() does not draw any image on the form.

Answer 1

Joshua,

The DateTimePicker control has some restrictions when it comes to custom painting, so you will probably have to go under the hood and override the Window Procedure of the control.

The following implementation uses an "off label" way of using the WM_PAINT message to draw on the control after the default painting has been done. Note that we usually don't call GetDC() or its equivalent Graphics.FromHwnd() when processing the WM_PAINT message, but in this case we don't want to override any part of the original painting. We merely want to draw our bitmap after it finishes its processing by the base procedure.

public partial class UserControl1 : System.Windows.Forms.DateTimePicker
{
    private Bitmap bmp = null;
    public UserControl1()
    {
        InitializeComponent();
        bmp = new Bitmap(5, 5);
        bmp.SetPixel(2, 2, Color.Red); //Placeholder, Load the bitmap here
    }
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == 0xf) //WM_PAINT message
        {
            Graphics g = Graphics.FromHwnd(m.HWnd);
            g.DrawImage(bmp, ClientRectangle.Width - 8, 3);
            g.Dispose();
        }
    }
}