Question

I have a user control with custom painting. Constructor sets styles correctly, from what I can tell. Basic code:

public partial class LineChart2 : UserControl
{
    public LineChart2()
    {
        InitializeComponent();

        //Set control styles to eliminate flicker on redraw and to redraw on resize
        this.SetStyle(
            ControlStyles.ResizeRedraw |
            ControlStyles.UserPaint |
            ControlStyles.AllPaintingInWmPaint |
            ControlStyles.DoubleBuffer,
            true);

        SetDefaultValues();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
    // breakpoint set here for verification
        Paint~misc stuff(e.Graphics);

        base.OnPaint(e);
    }

    private void UpdateGraph()
    {
    // this is called when the data that the control depends on changes
        ~update stuff();

        this.Invalidate();
        //this.Refresh();
    }
}

The control is contained within a Panel on a standard WinForm.

I’ve tried both Invalidate and Refresh.

When using Invalidate(), the control will redraw properly as long as the form it is contained in has focus. Drawing is smooth. When I switch focus to another form, drawing ceases even though the events are still firing, and this.Invalidate() is still being called. The form is still fully visible on screen.

When using Refresh(), the control will redraw regardless of whether the form has focus, but the drawing constantly flickers, as if bypassing the double-buffering mechanism.

So how do I get the Invalidate message to properly invoke the OnPaint method regardless of focus?

Answer 1

Documentation says:

Calling the Invalidate method does not
force a synchronous paint; to force a
synchronous paint, call the Update
method after calling the Invalidate
method.

Have you tried calling Update after Invalidate?