Paint event of panel not called when shrinking Form from right to left?

问题

I have a Form which has got a parent panel and it had got a child panel where I am drawing items using the drawing mechanism it works good as expected, but when I shrink my form from right to left it doesn't call child panels paint event while if I shrink a little from left to right and again spread it then it calls the paint event, how should I fix it? Below is my code.

  private void canvas_Paint(object sender, PaintEventArgs e)
        {
            drawString(e);
            this.Invalidate();
            //this.Refresh();
            //this.Update();


        }

        private void drawString(PaintEventArgs e)
        {

            System.Drawing.Drawing2D.LinearGradientBrush myBrush = new System.Drawing.Drawing2D.LinearGradientBrush(ClientRectangle, Color.Red, Color.Yellow, System.Drawing.Drawing2D.LinearGradientMode.Horizontal);
            cBasketItemHelper objHelper = new cBasketItemHelper() { CanvasWidth = this.canvas.Width, CanvasHeight = this.canvas.Height, X = 3, Y = 3 };
            objHelper.myBrush = myBrush;
            objHelper.currOrder = Program.currOrder;
            objHelper.g = e.Graphics;//this.canvas.();//this.canvas.Graphics;
            objHelper.DrawBasketItems();
            e.Dispose();
        }

回答1:

The Panel class was designed to be just a container for other controls, it is not expected to do any painting of its own beyond drawing the background. Somewhat heavy-handedly it optimizes the painting, a resize only paints the parts that were revealed, not the entire client area.

You however want OnPaint to always run when the size changes, even when you make it smaller. Derive your own class from Panel and set the ResizeRedraw property to true in the constructor:

class Canvas {
    public Canvas() {
        this.ResizeRedraw = true;
        this.DoubleBuffered = true;   // extra goodie
    }
}

Build. Drop the new Canvas control from the top of the toolbox, replacing your existing panel control. If you don't need the scrolling support that Panel provides then using a PictureBox gets you both without needing to derive.

来源：https://stackoverflow.com/questions/18717733/paint-event-of-panel-not-called-when-shrinking-form-from-right-to-left

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