利用GDI+在窗体上绘制线条,移动窗体到边缘后线条被擦除一部分,这个的解释是?

Question

GDI窗体重绘

Answer 1

你自己画的东西要放到OnPaint事件中，这样在重绘时才不会丢失，设置image后，picturebox在的onpaint中会自动DrawImage(this.image, rect); 源码如下，看最后面那几句代码protected override void OnPaint(PaintEventArgs pe)
{
    if (this.pictureBoxState[0x20])
    {
        try
        {
            if (this.WaitOnLoad)
            {
                this.Load();
            }
            else
            {
                this.LoadAsync();
            }
        }
        catch (Exception exception)
        {
            if (ClientUtils.IsCriticalException(exception))
            {
                throw;
            }
            this.image = this.ErrorImage;
        }
    }
    if (this.image != null)
    {
        this.Animate();
        ImageAnimator.UpdateFrames();
        Rectangle rect = (this.imageInstallationType == ImageInstallationType.ErrorOrInitial) ? this.ImageRectangleFromSizeMode(PictureBoxSizeMode.CenterImage) : this.ImageRectangle;
        pe.Graphics.DrawImage(this.image, rect);
    }
    base.OnPaint(pe);
} 

Answer 2

基本上就是你自己画线不一定都在系统重绘ui之后执行。放在onpaint里是一个办法，还有个简单办法把你画好的image作为backgroundimage赋值给窗体……那么系统就会把你画的内容作为窗体的一部分自动重绘了