Switching to another application (previously active) on button click in .net

Question

Hi I want to do something like on screen keyboard. I want user to click a button on inactive application and then key press will be sent to active application while keeping active application active. I wrote the code for hover event of the button in inactive application and it is working. But what I want is to do it in click event. It is not working because inactive application becomes active. The code is below for hover event. Thank you.

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private void button1_MouseHover(object sender, EventArgs e)
{
    SendKeys.Send("{TAB}");
}

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Answer 1

Finally I could figure out a way to do it. Refer the code below.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Diagnostics;
using System.Timers;
using tmr = System.Timers;
using System.Threading;

namespace KeyPressTest
{
    public partial class Form1 : Form
    {
        [DllImport("user32.dll")]
        static extern int GetForegroundWindow();

        [DllImport("user32")]
        private static extern UInt32 GetWindowThreadProcessId(Int32 hWnd, out Int32 lpdwProcessId);

        [DllImport("user32.dll")]
        static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        [System.Runtime.InteropServices.DllImport("user32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);

        tmr.Timer tm = new tmr.Timer();
        Int32 hwnd = 0;

        private Int32 GetWindowProcessID(Int32 hwnd)
        {
            Int32 pid = 1;
            GetWindowThreadProcessId(hwnd, out pid);
            return pid;
        }     

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            tm.Elapsed += Timer_Elapsed;
            tm.Interval = 100;
            tm.Start();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            SetForegroundWindow((IntPtr)hwnd);
            Thread.Sleep(40);
            SendKeys.Send("{TAB}");
        }       

        private void Timer_Elapsed(object sender, System.EventArgs args)
        {
            if (this.InvokeRequired)
            {
                this.Invoke(new MethodInvoker(delegate
                {
                    if (this.Handle.ToInt32() != GetForegroundWindow())
                    {
                        hwnd = GetForegroundWindow();
                    }
                }));
            }
            else
            {
                if (this.Handle.ToInt32() != GetForegroundWindow())
                {
                    hwnd = GetForegroundWindow();
                }
            }
            if (hwnd == 0)
            {
                return;
            }
            string appProcessName = "";
            string appExePath = "";
            string appExeName = "";
            try
            {
                appProcessName = Process.GetProcessById(GetWindowProcessID(hwnd)).ProcessName;
                appExePath = Process.GetProcessById(GetWindowProcessID(hwnd)).MainModule.FileName;
                appExeName = appExePath.Substring(appExePath.LastIndexOf(@"\") + 1);
            }
            catch (Exception ex)
            {
            }
            if (textBox1.InvokeRequired)
            {
                textBox1.Invoke(new MethodInvoker(delegate
                {
                    textBox1.Text = appProcessName + " | " + appExePath + " | " + appExeName;
                }));
            }
            else
            {
                textBox1.Text = appProcessName + " | " + appExePath + " | " + appExeName;
            }
        }
    }
}