C# Signature:

[DllImport("user32.dll")]

private static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

VB Signature:

Declare Function SendMessage Lib "coredll.dll" (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As IntPtr

Notes:

If you are searching for a way to send keys to an application, you can use System.Windows.Forms.SendKeys.Send(keys) after bringing the window to the top via the SetForegroundWindow API.

Tips & Tricks:

Sample Code:

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

    private void button1_Click(object sender, EventArgs e)
    {
    //Down
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYDOWN, (int)User32.VK.VK_DOWN, 0);
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYUP, (int)User32.VK.VK_DOWN, 0);
    }

    private void button2_Click(object sender, EventArgs e)
    {
    //Up
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYDOWN, (int)User32.VK.VK_UP, 0);
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYUP, (int)User32.VK.VK_UP, 0);
    }

    //Left ... Right...
    }

    class User32
    {
    [System.Runtime.InteropServices.DllImport("coredll.dll")]
    public static extern int SendMessage(IntPtr hWnd, WM Msg, int wParam, int lParam);

    public enum VK : int
    private void button2_Click(object sender, EventArgs e)
    {
    VK_DOWN = 0x28,
    VK_UP = 0x26,
    VK_LEFT = 0x25,
    VK_RIGHT = 0x27
    }
    //Up
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYDOWN, (int)User32.VK.VK_UP, 0);
    User32.SendMessage(listView1.Handle, User32.WM.WM_KEYUP, (int)User32.VK.VK_UP, 0);

    public enum WM
    {
    WM_KEYUP = 0x0101,
    WM_KEYDOWN = 0x0100
    }
    }
    //Left ... Right...

    }

    private void Form1_Load(object sender, EventArgs e)
    {

    }
    }

    class User32
    {
    [System.Runtime.InteropServices.DllImport("coredll.dll")]
    public static extern int SendMessage(IntPtr hWnd, WM Msg, int wParam, int lParam);

    public enum VK : int
    {
    VK_DOWN = 0x28,
    VK_UP = 0x26,
    VK_LEFT = 0x25,
    VK_RIGHT = 0x27
    }

    public enum WM
    {
    WM_KEYUP = 0x0101,
    WM_KEYDOWN = 0x0100
    }
    }

Alternative Managed API:

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