SendKeys alternative that works on Citrix

Question

I recently developed a virtual keyboard application for a customer. The program is working fine with almost all programs, but certain commands like {ENTER} or <

Answer 1

Try to utilize API call wia P-Invoke signature (Content edited: this is now working example - I'm sending character 'a' to the textBox, on the click of a button) :

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;
using System.Runtime.InteropServices;

namespace Test2
{
    public partial class Form1 : Form
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct KEYBOARD_INPUT
        {
            public const uint Type = 1;
            public ushort wVk;
            public ushort wScan;
            public uint dwFlags;
            public uint time;
            public IntPtr dwExtraInfo;
        }  

        [StructLayout(LayoutKind.Sequential)]
        struct MOUSEINPUT
        {
             public int dx;
             public int dy;
             public uint mouseData;
             public uint dwFlags;
             public uint time;
             public IntPtr dwExtraInfo;
        };

        [StructLayout(LayoutKind.Explicit)]
        struct KEYBDINPUT 
        {
            [FieldOffset(0)]
            public ushort wVk;
            [FieldOffset(2)]
            public ushort wScan;
            [FieldOffset(4)]
            public uint dwFlags;
            [FieldOffset(8)]
            public uint time;
            [FieldOffset(12)]
            public IntPtr dwExtraInfo;
        };

        [StructLayout(LayoutKind.Sequential)]
        struct HARDWAREINPUT
        {
             public uint uMsg;
             public ushort wParamL;
             public ushort wParamH;
        };

        [StructLayout(LayoutKind.Explicit)]
        struct INPUT 
        {
             [FieldOffset(0)]
             public int type;
             [FieldOffset(4)]
             public MOUSEINPUT mi;
             [FieldOffset(4)]
             public KEYBDINPUT ki;
             [FieldOffset(4)]
             public HARDWAREINPUT hi;
        };
        [DllImport("user32.dll", SetLastError = true)]
        static extern uint SendInput(uint nInputs, IntPtr pInput, int cbSize);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Focus();
            INPUT Input = new INPUT();

            Input.type = 1;
            Input.ki.wVk = 0x41;  //ASCII for letter 'A'
            Input.ki.dwFlags = 0;  //Key is pressed down
            Input.ki.dwExtraInfo = IntPtr.Zero;
            IntPtr pInput;
            pInput = Marshal.AllocHGlobal(Marshal.SizeOf(Input));

            Marshal.StructureToPtr(Input, pInput, false);
            SendInput(1, pInput, Marshal.SizeOf(Input));
            Input.ki.dwFlags = 2;  //Key is released on the keyboard

            Marshal.StructureToPtr(Input, pInput, false);
            SendInput(1, pInput, Marshal.SizeOf(Input));
        }
    }
}