[Solved] How to retain previous graphics in paint event?

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The simplest way is for you to create an ordered collection of objects (a List<> for example) which you would redraw each time that the OnPaint event is called.

Something like:

    // Your painting class. Only contains X and Y but could easily be expanded
    // to contain color and size info as well as drawing object type.
    class MyPaintingObject
    {
        public int X { get; set; }
        public int Y { get; set; }
    }

    // The class-level collection of painting objects to repaint with each invalidate call
    private List<MyPaintingObject> _paintingObjects = new List<MyPaintingObject>();

    // The UI which adds a new drawing object and calls invalidate
    private void button1_Click(object sender, EventArgs e)
    {
        // Hardcoded values 10 & 15 - replace with user-entered data
        _paintingObjects.Add(new MyPaintingObject{X=10, Y=15});
        panel1.Invalidate();
    }

    private void panel1_Paint(object sender, PaintEventArgs e)
    {
        // loop through List<> and paint each object
        foreach (var mpo in _paintingObjects)
            e.Graphics.FillEllipse(Brushes.Red, mpo.X, mpo.Y, 20, 20);
    }

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solved How to retain previous graphics in paint event?