How to loop through all controls in a Windows Forms form or how to find if a particular control is a container control?

Question

I will tell my requirement. I need to have a keydown event for each control in the Windows Forms form. It's better to do so rather than manually doing it for all controls if what I have to do for all keydown events is the same.

So I could basically do this:

foreach (Control c in this.Controls)
    c.KeyDown+= new KeyEventHandler(c_KeyDown);

But here, the foreach doesn't loop inside those controls which reside inside a groupBox or a tabControl. I mean if the form (this) contains a groupBox or some other container control, then I can get a keydown event for that particular container control. And the foreach doesn't loop through controls that reside inside that container control.

Question 1: How do I get a keydown event for "all" the controls in a form?

If the above puzzle is solved, then my problem is over.

This is what I can otherwise do:

Mainly pseudo code

foreach (Control c in this.Controls)
{
     c.KeyDown += new KeyEventHandler(c_KeyDown);

     if (c is Container control)
           FunctionWhichGeneratesKeyDownForAllItsChildControls(c)
}

I know I will have to go through FunctionWhichGeneratesKeyDownForAllItsChildControls(c) many times over to get keydown for all controls if there are groupboxes inside a groupbox or so. I can do it. My question is,

Question 2: How do I check if c is a container control?

Answer 1

A simple recursive function should do it.

private void AddEvent(Control parentCtrl)
{
  foreach (Control c in parentCtrl.Controls)
  {
    c.KeyDown += new KeyEventHandler(c_KeyDown);
    AddEvent(c);
  }
}

Answer 2

This is the same as Magnus' correct answer but a little more fleshed out. Note that this adds the handler to every control, including labels and container controls. Those controls do not appear to raise the event, but you may want to add logic to only add the handler to controls that accept user input.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        RegisterKeyDownHandlers(this);
    }

    private void RegisterKeyDownHandlers(Control control)
    {
        foreach (Control ctl in control.Controls)
        {
            ctl.KeyDown += KeyDownFired;
            RegisterKeyDownHandlers(ctl);
        }
    }

    private void KeyDownFired(object sender, EventArgs e)
    {
        MessageBox.Show("KeyDown fired for " + sender);
    }
}

Answer 3

Here are some non-recursive options for traversing the control collection. My particular implementation is doing interface validation, but could be adapted to your purpose.

Why even mess with a non-recursive solution you say? Well I got a stack overflow error when debugging one day, so I looked at replacing it with a loop (which is considerably more difficult). As it turns out that error was a fluke and has never happened again

    //recursive
    //This is the simplest implementation, but the most memory hungry
    private IEnumerable<DataObjects.Error> CheckErrors(Control.ControlCollection controls, ErrorProvider errorProvider)
    {
        var errors = new List<DataObjects.Error>();
        foreach (var control in controls.Cast<System.Windows.Forms.Control>())
        {
            //insert your own business logic in here
            var error = errorProvider.GetError(control);
            if (!string.IsNullOrEmpty(error))
            {
                errors.Add(new DataObjects.Error(error, DataObjects.ErrorLevel.Validation));
            }
            //recursive call
            errors.AddRange(CheckErrors(control.Controls, errorProvider));
            //insert your own business logic in here
        }
        return errors;
    }

    //Breadth first - Does NOT require child node to have knowledge of parent
    //Read through the controls at a given level and then blindly delve 
    //deeper until you reach the end of the rainbow
    //order(max-tree-level-size) memory usage?
    //tree-level-size, as in the # of nodes at a given depth
    private IEnumerable<DataObjects.Error> CheckErrors_NonRecursive_NeverLookBack(Control control, ErrorProvider errorProvider)
    {
        var currentControls = control.Controls.Cast<Control>();
        var errors = new List<DataObjects.Error>();

        while (currentControls.Count() > 0)
        {
            foreach (var currentControl in currentControls)
            {
                //insert your own business logic in here
                var error = errorProvider.GetError(currentControl);
                if (!string.IsNullOrEmpty(error))
                {
                    errors.Add(new DataObjects.Error(error, DataObjects.ErrorLevel.Validation));
                }
                //insert your own business logic in here
            }
            //replace currentControls with ALL of the nodes at a given depth
            currentControls = currentControls.SelectMany(x => x.Controls.Cast<Control>());
        }

        return errors;
    }

    //Depth first - Does NOT require child to have knowledge of parent
    //Approximate recursion by keeping a stack of controls, instead of a call stack.
    //Traverse the stack as you would have with recursion
    //order(tree-branch-size) memory usage? tree-branch-size as in the number of nodes 
    //that it takes to get from the root to the bottom of a given branch
    private IEnumerable<DataObjects.Error> CheckErrors_NonRecursive(Control.ControlCollection controls, ErrorProvider errorProvider)
    {
        var controlStack = new Stack<Control.ControlCollection>();
        var controlIndicies = new Stack<int>();
        var errors = new List<DataObjects.Error>();

        controlStack.Push(controls);
        controlIndicies.Push(0);

        while(controlStack.Count() > 0)
        {
            while(controlIndicies.First() < controlStack.First().Count)
            {
                var controlIndex = controlIndicies.Pop();
                var currentControl = controlStack.First()[controlIndex];
                //insert your own business logic in here
                var error = errorProvider.GetError(currentControl);
                if (!string.IsNullOrEmpty(error))
                {
                    errors.Add(new DataObjects.Error(error, DataObjects.ErrorLevel.Validation));
                }
                //insert your own business logic in here

                //update the fact that we've processed one more control
                controlIndicies.Push(controlIndex + 1);
                if(currentControl.Controls.Count > 0)
                {
                    //traverse deeper
                    controlStack.Push(currentControl.Controls);
                    controlIndicies.Push(0);
                }
                //else allow loop to continue uninterrupted, to allow siblings to be processed
            }
            //all siblings have been traversed, now we need to go back up the stack
            controlStack.Pop();
            controlIndicies.Pop();
        }

        return errors;
    }

    //Depth first - DOES require child to have knowledge of parent.
    //Approximate recursion by keeping track of where you are in the control 
    //tree and use the .Parent() and .Controls() methods to traverse the tree.
    //order(depth(tree)) memory usage? 
    //Best of the bunch as far as I can (in memory usage that is)
    private IEnumerable<DataObjects.Error> CheckErrors_NonRecursiveIndicesOnly(Control control, ErrorProvider errorProvider)
    {
        var errors = new List<DataObjects.Error>();
        var controlIndicies = new Stack<int>();
        var controlCount = new Stack<int>();
        Control currentControl = control;
        var currentControls = currentControl.Controls;

        controlCount.Push(currentControls.Count);
        controlIndicies.Push(0);
        while (controlCount.Count() > 0)
        {
            while (controlIndicies.First() < controlCount.First())
            {
                var controlIndex = controlIndicies.Pop();
                currentControl = currentControls[controlIndex];
                //insert your own business logic in here
                var error = errorProvider.GetError(currentControl);
                if (!string.IsNullOrEmpty(error))
                {
                    errors.Add(new DataObjects.Error(error, DataObjects.ErrorLevel.Validation));
                }
                //insert your own business logic in here

                //update the fact that we've processed one more control
                controlIndicies.Push(controlIndex + 1);
                if (currentControl.Controls.Count > 0)
                {
                    //traverse deeper
                    currentControls = currentControl.Controls;
                    controlCount.Push(currentControl.Controls.Count);
                    controlIndicies.Push(0);
                }
                else
                {
                    //allow loop to continue uninterrupted, to allow siblings to be processed
                }
            }
            //all siblings have been traversed, now we need to go back up the stack
            controlCount.Pop();
            controlIndicies.Pop();

            //need to check our position in the stack... once we get back to the top there is no parent of parent.
            if (controlCount.Count() > 0)
            {
                currentControls = currentControl.Parent.Parent.Controls;
            }
            //do nothing, believe it or not once you've gotten to this level you have traversed the entire stack
        }

        return errors;
    }

Answer 4

The answer to question 2 is to use the GetType() method of the control you are checking.