How to find previous active control c#

Question

i am developing keyboard control, very simple embedded on a form. using sendkey class to perform char entry. to make this functional is required to know previous selected control.

Answer 1

Something like the following should do the trick:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace DragDropTest
{
    public partial class LostFocusTestForm : Form
    {
        private Control _lastControl;

        public LostFocusTestForm()
        {
            InitializeComponent();

            TrapLostFocusOnChildControls(this.Controls);
        }
        private void finalTextBox_Enter(object sender, EventArgs e)
        {
            MessageBox.Show("From " + _lastControl.Name + " to " + this.ActiveControl.Name);
        }

        private void AllLostFocus(object sender, EventArgs e)
        {
            _lastControl = (Control)sender;
        }

        private void TrapLostFocusOnChildControls(Control.ControlCollection controls)
        {
            foreach (Control control in controls)
            {
                control.LostFocus += new EventHandler(AllLostFocus);

                Control.ControlCollection childControls = control.Controls;
                if (childControls != null)
                    TrapLostFocusOnChildControls(childControls);
            }
        }
    }
}

Answer 2

Expanding on David's answer. This is how you can use the Enter event and a variable to store the last control:

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        Control lastControlEntered = null;

        public Form1()
        {
            InitializeComponent();

            foreach (Control c in Controls)
                if (!(c is Button)) c.Enter += new EventHandler(c_Enter);
        }

        void c_Enter(object sender, EventArgs e)
        {
            if (sender is Control)
                lastControlEntered = (Control)sender;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            label1.Text = lastControlEntered == null ? "No last control" : lastControlEntered.Name;
        }
    }
}

To run this code, add a few textboxes and other control to a Form in Visual Studio, and add a button and a label and attach the button's click handler to button1_Click. When you press the button, the last control you were in before pressing the button is displayed in the label. Edit this code to suit your needs.