Question

我正在使用

e.Graphics.FillEllipse(Brushes.Red, ph1.X,ph1.Y, 20, 20);

在panel1_Paint事件中

绘制椭圆。点ph1值来自textbox_KeyPress。

我还在textbox_KeyPress事件中添加了panel1.Invalidate();以强制重绘panel1。它正在做的是清除panel1然后添加新图形。

我真正希望它做的是添加新图形而不清除以前的图形。

是否有方法？

Answer 1

最简单的方法是创建一个有序的对象集合（例如List＆lt;＆gt;），每次调用OnPaint事件时都会重绘它。

类似的东西：

    // 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);
    }

如何在paint事件中保留以前的图形？

1 个答案: