使用CreateGraphics()交换窗口时，行会被擦除 [英] line get erased when window is swaped using CreateGraphics()

问题描述

大家好

我是CreateGraphics主题的新手.我有一个简单的图形"应用程序，在该应用程序中，我通过在窗口的2个不同点上单击鼠标来绘制一条线.这条线画在窗户上.但是我的问题是，当我切换到另一个窗口时，n会回到我的项目中，该窗口将被清除.我之前绘制的线条将不存在
因此，如果您有任何建议，请告诉我.我的代码就是这样

Hello every one

i m new to CreateGraphics topic . i have a simple Graphics application where i draw a line by mouse clicked at 2 different points over the window . the line is drawn over the window . But my problem is when i switch over to other window n come back to my project the window is cleared . My previous drawn lines will be not there
so if u have any suggestion kindly let me know it . My codes are like this

public Form1()
        {
            InitializeComponent();
        }
        Point[] pts;
        int pointcount = 0;
        private void Form1_MouseClick(object sender, MouseEventArgs e)
        {
            if (pointcount == 0)
                pts = new Point[2];

            if (e.Button == MouseButtons.Left)
            {
                if (pointcount != 2)
                {
                    pts[pointcount].X = e.X;
                    pts[pointcount].Y = e.Y;
                    ++pointcount;
                }
                else
                    pointcount = 0;

                if (pointcount == 2)
                {
                    ghx.DrawCurve(Pens.Black, pts);
                    pointcount = 0;
                }


            }
        }
        Graphics ghx;
        private void Form1_Load(object sender, EventArgs e)
        {
            ghx = CreateGraphics();
        }

推荐答案

您必须能够在绘制事件中重绘图形.因此，通常，您会将行存储在容器中(还有正在进行中的行的信息).

OnPaint [

You have to be able to redraw your Graphics in paint event. Thus typically, you would store your lines in a container (and also information for the line in progress).

OnPaint[^]

当然可以！ Form不保存图形.这是有充分理由的.表单在每次部分无效时都会呈现，这种情况发生在表单的一部分被其他窗口遮罩并随后显示时.
您需要处理事件Form.Paint或重写其方法Form.OnPaint.例如，将此代码放在表单的构造函数中:

Of course! The Form does not hold graphics; and this is done so for a good reason. The form is rendered every time part of it is invalidated, which happens when a part of form is shown when it was masked by some other window and later shown.

You need to handle the event Form.Paint or override its method Form.OnPaint. For example, place this code in your form''s constructor:

this.Paint += (sender, eventArgs) => {
   Graphics graphics = eventArgs.Graphics;
   //use this instance of Graphics to render the scene
};

根据经验，不应创建System.Drawing.Graphics的实例，而应使用事件参数parameter中传递给您的实例.

现在，要更改渲染的图形(动画，任何形式的交互行为，例如在游戏或绘图应用程序中)，请根据某些数据结构设置渲染方法(如上图所示，作为匿名方法)；并使该数据结构成为您表单的一个或多个字段.当您更改数据时，渲染将更改；但是如何触发重新绘制?您需要触发将消息WM_PAINT发送到表单.

这是通过调用Form.Invalidate(继承自Control.Invalidate)来完成的.您可以使用带有参数(Rectangle或Region)的Invalidate来提高性能，以使场景的仅一部分无效.

—SA

As a rule of thumb, you should not create an instance of System.Drawing.Graphics, use the one passed to you in event arguments parameter.

Now, to change the rendered graphics (animation, any kind of interactive behavior such as in gaming or drawing application) make the rendering method (shown as anonymous method above) depending on some data structure; and make this data structure a field(s) of your form. When you change data, the rendering will change; but how to trigger re-drawing? You need to trigger sending the message WM_PAINT to the form.

This is done by calling Form.Invalidate (inherited from Control.Invalidate. You can improve performance using Invalidate with parameters (Rectangle or Region) to invalidate just some part of the scene.

—SA

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