How to handle Keydown event in Form level after All Child controls handled it?

Question

I have a form with two controls A and B , A has a key-down event and i show a message box when 'S' is pressed on A control. And i want to show another message when 'S' is pressed in any other control.

how can I do this ?

Simply what I want is : I should be able to handle a Key-down event after all child controls. and I should be able to know whether the Event is handle in a child control in Form-level Key-down.

I tried enabling Key-preview but when Key-preview is enabled Form-level event get's fired before child control events. I want child controls first, Then Form level one

I want form level Event to be fired after focused control's key down event is fired. and I want to check in Form-level event whether the event is handled in focused controls key-down event.

What methods can I use for this ?

Please enlighten me.

Answer 1

you can do the following

here a sample code

1. Add new project call it EventSample
2. Add a UserControl call it AControl
3. Add a UserControl call it BControl
4. make the AControl BackColor Blue and BControl Red in order to distinguish from the form

//Form1 code

namespace EventSample
{
    public delegate void AfterChildEventHandler(Control control,Keys key);
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            aControl1.OnChildFireEvent += OnChildFireEvent;
            bControl1.OnChildFireEvent += OnChildFireEvent;
        }

        void OnChildFireEvent(Control control, Keys key)
        {
            MessageBox.Show("Form fired event from " + control.GetType().Name);
        }
    }
}

//AControl code

namespace EventSample
{
    public partial class AControl : UserControl
    {
        public event AfterChildEventHandler OnChildFireEvent;
        public AControl()
        {
            InitializeComponent();
        }

        private void AControl_KeyDown(object sender, KeyEventArgs e)
        {
            MessageBox.Show("A Control fired Key down");
            if (OnChildFireEvent != null)
                OnChildFireEvent(this, e.KeyCode);
        }
    }
}

//BControl code

public partial class BControl : UserControl
    {
        public event AfterChildEventHandler OnChildFireEvent;
        public BControl()
        {
            InitializeComponent();
        }

        private void BControl_KeyDown(object sender, KeyEventArgs e)
        {
            MessageBox.Show("B Control fired Key down");
            if (OnChildFireEvent != null)
                OnChildFireEvent(this, e.KeyCode);
        }
    }

EDITED

another solution you can make it with less code

1. define a static event
2. handle this event inside the form

3. let each control to invoke this event

   namespace EventSample {

   public delegate void AfterChildEventHandler(Control control, Keys key);
   
   public class GlobalEvent
   {
       public static event AfterChildEventHandler OnChildEventFire;
   
       public static void Invoke(Control control, Keys key)
       {
           if (OnChildEventFire != null)
               OnChildEventFire(control, key);
       }
   }
   

   }

changes in the A Control

namespace EventSample
{
    public partial class AControl : UserControl
    {
        public AControl()
        {
            InitializeComponent();
        }

        private void AControl_KeyDown(object sender, KeyEventArgs e)
        {
            MessageBox.Show("A Control fired Key down");
            GlobalEvent.Invoke(this, e.KeyCode);
        }
    }
}

changes in the B Control

namespace EventSample
{
    public partial class BControl : UserControl
    {
        public BControl()
        {
            InitializeComponent();
        }

        private void BControl_KeyDown(object sender, KeyEventArgs e)
        {
            MessageBox.Show("B Control fired Key down");
            GlobalEvent.Invoke(this, e.KeyCode);
        }
    }
}

Build the sample and run and try to press any key on A or B then you will find that A will fire then the form

hope it will help you