如何在绘制事件中保留以前的图形? [英] How to retain previous graphics in paint event?

问题描述

我正在使用

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

在panel1_Paint 事件中绘制一个椭圆.点 ph1 值来自 textbox_KeyPress.

in the panel1_Paint event to draw an ellipse. The point ph1 value comes from textbox_KeyPress.

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

I also added panel1.Invalidate(); in the textbox_KeyPress event to force redraw on panel1. What it is doing is clearing panel1 then add the new graphics.

我真正想让它做的是在不清除以前的图形的情况下添加新图形.

有什么方法吗?

推荐答案

最简单的方法是创建一个有序的对象集合(例如 List<>)，每次调用 OnPaint 事件时都会重绘这些对象.

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.

类似于:

    // 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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