在遍历子控件时避免无限循环

Question

我正在编写一个简单的扩展方法来对控件及其所有子控件执行操作，我想知道我是否必须担心两次遇到同一个控件。

安全：

public static void Traverse(this Control control, Action<Control> action)
{
    Traverse(control, action, new HashSet<control>());
}

private static void Traverse(this Control control, Action<Control> action, HashSet<Control> handled)
{
    handled.Add(control);
    foreach (Control child in control.Controls)
        if (!handled.Contains(child))
            Traverse(child, action, handled);
    action.Invoke(control);
}

可能不安全：

public static void Traverse(this Control control, Action<Control> action)
{
    foreach (Control child in control.Controls)
        Traverse(child, action, handled);
    action.Invoke(control);
}

散列集是保证这段代码安全所必需的吗？每个控件只需要调用一次动作，不能进入死循环。是不是父子控件的结构这样我就不用担心了？

用法：

this.Traverse(o => o.SuspendLayout());

// Do lots of UI changes

this.Traverse(o => o.ResumeLayout());

---

执行此操作的（可能）综合方法：

public static class ControlExtensions
{
    public static void Traverse(this Control control, Action<Control> action)
    {
        Traverse(control, action, TraversalMethod.DepthFirst);
    }

    public static void Traverse(this Control control, Action<Control> action, TraversalMethod method)
    {
        switch (method)
        {
            case TraversalMethod.DepthFirst:
                TraverseDepth(control, action);
                break;
            case TraversalMethod.BreadthFirst:
                TraverseBreadth(control, action);
                break;
            case TraversalMethod.ReversedDepthFirst:
                TraverseDepthReversed(control, action);
                break;
            case TraversalMethod.ReversedBreadthFirst:
                TraverseBreadthReversed(control, action);
                break;
        }
    }

    private static void TraverseDepth(Control control, Action<Control> action)
    {
        Stack<Control> controls = new Stack<Control>();
        Queue<Control> queue = new Queue<Control>();

        controls.Push(control);
        while (controls.Count != 0)
        {
            control = controls.Pop();
            foreach (Control child in control.Controls)
                controls.Push(child);
            queue.Enqueue(control);
        }
        while (queue.Count != 0)
            action.Invoke(queue.Dequeue());
    }

    private static void TraverseBreadth(Control control, Action<Control> action)
    {
        Queue<Control> controls = new Queue<Control>();
        Queue<Control> queue = new Queue<Control>();

        controls.Enqueue(control);
        while (controls.Count != 0)
        {
            control = controls.Dequeue();
            foreach (Control child in control.Controls)
                controls.Enqueue(child);
            queue.Enqueue(control);
        }
        while (queue.Count != 0)
            action.Invoke(queue.Dequeue());
    }

    private static void TraverseDepthReversed(Control control, Action<Control> action)
    {
        Stack<Control> controls = new Stack<Control>();
        Stack<Control> stack = new Stack<Control>();

        controls.Push(control);
        while (controls.Count != 0)
        {
            control = controls.Pop();
            foreach (Control child in control.Controls)
                controls.Push(child);
            stack.Push(control);
        }
        while (stack.Count != 0)
            action.Invoke(stack.Pop());
    }

    private static void TraverseBreadthReversed(Control control, Action<Control> action)
    {
        Queue<Control> controls = new Queue<Control>();
        Stack<Control> stack = new Stack<Control>();

        controls.Enqueue(control);
        while (controls.Count != 0)
        {
            control = controls.Dequeue();
            foreach (Control child in control.Controls)
                controls.Enqueue(child);
            stack.Push(control);
        }
        while (stack.Count != 0)
            action.Invoke(stack.Pop());
    }
}

Answer 1

每个孩子都有一个父母，因此无需担心。

Answer 2

控件实际上只能有一个父级。实际上没有理由跟踪“已处理”，因为您只会在控件上执行您的方法一次。

现在，如果您使用的框架允许控件有多个父级（我不知道有任何 .NET 框架允许这样做），那么这可能是必需的。但是，如果您使用的是 Windows 窗体（看起来就是这样）或 WPF，您可以将其简化为：

private static void Traverse(this Control control, Action<Control> action)
{
    foreach (Control child in control.Controls)
        Traverse(child, action);
    action(control);
}

Answer 3

你需要使用递归

public sub DoStuffToControlAndChildren(TargetControl as Control)

    'Insert code to do stuff to TargetControl here

     if TargetControl.Controls.count = 0 then
         return
     end if 

     For each ChildControl in TargetControl.Controls
        DoStuffToControlAndChildren(ChildControl)
     next

end sub