为什么当两个自定义控件都添加了计时器时，设计器会变慢

Question

我有一个用于长时间进程的自定义控件。此控件具有围绕一个点旋转的圆。为了做到这一点，我使用的定时器是在设计时和运行时工作。当一个控件被添加到表单中时，没有问题。但其中两个是添加到形式中的，设计师放慢了速度。为什么会出现此问题，我该如何解决？

我的代码来自这个项目：

 public class SpinningCircles : Control
{
    bool fullTransparency = true;
    int increment = 1;
    int radius = 4;
    int n = 8;
    int next = 0;
    int k = 0;
    Timer timer;
    public SpinningCircles()
    {
        timer = new Timer();
        timer.Tick += timer_Tick;
        timer.Enabled = true;
        SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.ResizeRedraw | ControlStyles.UserPaint | ControlStyles.SupportsTransparentBackColor, true);
        BackColor = Color.Transparent;
    }
    void timer_Tick(object sender, EventArgs e)
    {
        Invalidate();
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        if (fullTransparency)
        {
            Transparencer.MakeTransparent(this, e.Graphics);
        }
        e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
        int length = Math.Min(Width, Height);
        PointF center = new PointF(length / 2, length / 2);
        int bigRadius = length / 2 - radius - (n - 1) * increment;
        float unitAngle = 360 / n;
        next++;
        next = next >= n ? 0 : next;
        int a = 0;
        for (int i = next; i < next + n; i++)
        {
            int factor = i % n;
            float c1X = center.X + (float)(bigRadius * Math.Cos(unitAngle * factor * Math.PI / 180));
            float c1Y = center.Y + (float)(bigRadius * Math.Sin(unitAngle * factor * Math.PI / 180));
            int currRad = radius + a * increment;
            PointF c1 = new PointF(c1X - currRad, c1Y - currRad);
            e.Graphics.FillEllipse(Brushes.Black, c1.X, c1.Y, 2 * currRad, 2 * currRad);
            using (Pen pen = new Pen(Color.White, 2))
                e.Graphics.DrawEllipse(pen, c1.X, c1.Y, 2 * currRad, 2 * currRad);
            a++;
        }
    }
    protected override void OnVisibleChanged(EventArgs e)
    {
        timer.Enabled = Visible;
        base.OnVisibleChanged(e);
    }
    public bool FullTransparent
    {
        get
        {
            return fullTransparency;
        }
        set
        {
            fullTransparency = value;
        }
    }
}
public class Transparencer
{
    public static void MakeTransparent(Control cont, Graphics g)
    {
        if (cont.Parent != null)
        {
            Bitmap behind = new Bitmap(cont.Parent.Width, cont.Parent.Height);
            foreach (Control c in cont.Parent.Controls)
                if (c.Bounds.IntersectsWith(c.Bounds) & c != cont)
                    c.DrawToBitmap(behind, c.Bounds);
            g.DrawImage(behind, -cont.Left, -cont.Top);
            behind.Dispose();
        }
    }
}

Answer 1

为什么会出现此问题，我该如何解决？

这个问题与设计时间和计时器没有任何共同之处，而是MakeTransparent方法的错误实现。

首先，条件中有一个明显的错误

c.Bounds.IntersectsWith(c.Bounds)

此错误的影响是它为除调用者之外的每个控件调用c.DrawToBitmap。但是DrawToBitmap触发OnPaint，所以当另一个控件也是SpinningCircles时，它也会执行同样的操作，所以它会命中当前调用方，最终导致无限的OnPaint循环。

使用预期修复条件

c.Bounds.IntersectsWith(cont.Bounds)

将在两个自定义控件不重叠时尽快解决此问题。

整个实施是不正确的。一开始不应该这样做，但一旦这样做了，它至少应该只为与调用者相交且ZOrder较低的控件调用DrawToBitmap。类似这样的东西：

public static void MakeTransparent(Control control, Graphics g)
{
    var parent = control.Parent;
    if (parent == null) return;
    var bounds = control.Bounds;
    var siblings = parent.Controls;
    int index = siblings.IndexOf(control);
    Bitmap behind = null;
    for (int i = siblings.Count - 1; i > index; i--)
    {
        var c = siblings[i];
        if (!c.Bounds.IntersectsWith(bounds)) continue;
        if (behind == null)
            behind = new Bitmap(control.Parent.ClientSize.Width, control.Parent.ClientSize.Height);
        c.DrawToBitmap(behind, c.Bounds);
    }
    if (behind == null) return;
    g.DrawImage(behind, control.ClientRectangle, bounds, GraphicsUnit.Pixel);
    behind.Dispose();
}