C# Signature::

[DllImport("shell32.dll", CharSet = CharSet.Auto)]
static extern bool ShellExecuteEx(ref SHELLEXECUTEINFO lpExecInfo);

VB.NET Signature:

<DllImport("Shell32", CharSet:=CharSet.Auto, SetLastError:=True)> _
Public Function ShellExecuteEx(ByRef lpExecInfo As SHELLEXECUTEINFO) As Boolean
End Function

User-Defined Types:

(VB.NET)

Public Structure SHELLEXECUTEINFO
    Public cbSize As Integer
    Public fMask As Integer
    Public hwnd As IntPtr
    <MarshalAs(UnmanagedType.LPStr)> Public lpVerb As String
    <MarshalAs(UnmanagedType.LPStr)> Public lpFile As String
    <MarshalAs(UnmanagedType.LPStr)> Public lpParameters As String
    <MarshalAs(UnmanagedType.LPStr)> Public lpDirectory As String
    Dim nShow As Integer
    Dim hInstApp As IntPtr
    Dim lpIDList As IntPtr
    <MarshalAs(UnmanagedType.LPStr)> Public lpClass As String
    Public hkeyClass As IntPtr
    Public dwHotKey As Integer
    Public hIcon As IntPtr
    Public hProcess As IntPtr
End Structure

(C#)

    [StructLayout(LayoutKind.Sequential)]
    public struct SHELLEXECUTEINFO
    {
        public int cbSize;
        public uint fMask;
        public IntPtr hwnd;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpVerb;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpFile;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpParameters;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpDirectory;
        public int nShow;
        public IntPtr hInstApp;
        public IntPtr lpIDList;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpClass;
        public IntPtr hkeyClass;
        public uint dwHotKey;
        public IntPtr hIcon;
        public IntPtr hProcess;
    }

Notes:

Check the SW constants at to see what value to pass in the nShow member. Typically you'll pass SW_SHOW.

Be careful with the string structure fields: UnmanagedType.LPTStr will be marshalled as unicode string so only the first character will be recognized by the function. Use UnmanagedType.LPStr instead. [Tested on Win7]

lpVerb member can be used for a varity of actions like "properties", "find", "openas", "print"..etc depending on the file type you're dealing with.Actions available for a specific file type are stored in registry, setting lpVerb to null results in the default action of that file type to be executed.

The MSDN suggests that the various string members of SHELLEXECUTEINFO are all LPCTSTRs. Don't believe it: the truth is in the headers - in this case ShellAPI.h, which declares them all as LPCSTR i.e. they're always ANSI not Unicode.

Tips & Tricks:

(C#)

using System.Runtime.InteropServices;

(VB.NET)

Imports System.Runtime.InteropServices

Sample Code:

VB.NET

Demonstrates how to open an HTML file in the browser:

Dim info As SHELLEXECUTEINFO
info.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(info)
info.lpVerb = "open"
info.lpFile = "somefile.html"
info.nShow = SW_SHOW
If Not ShellExecuteEx(info) Then
     Dim ex As New System.ComponentModel.Win32Exception(System.Runtime.InteropServices.Marshal.GetLastWin32Error())
     MessageBox.Show(ex.Message, "Error")
End If

Alternative Managed API:

The Process class uses ShellExecuteEx by default:

Dim p As New Process
p.StartInfo.FileName = "somefile.html"
p.StartInfo.ErrorDialog = True ' this opens the "Open With" dialog for unknown file types
p.Start()

C# Example of Property Dialog

private const int SW_SHOW = 5;
private const uint SEE_MASK_INVOKEIDLIST = 12;

[DllImport("shell32.dll")]
static extern bool ShellExecuteEx(ref SHELLEXECUTEINFO lpExecInfo);

public static void ShowFileProperties(string Filename) {
    SHELLEXECUTEINFO info = new SHELLEXECUTEINFO();
    info.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(info);
    info.lpVerb = "properties";
    info.lpFile = Filename;
    info.nShow = SW_SHOW;
    info.fMask = SEE_MASK_INVOKEIDLIST;
    ShellExecuteEx(ref info);
}

VB.NET Example of Property Dialog

Public Const SW_SHOW As Short = 5
Public Const SEE_MASK_INVOKEIDLIST As Short = 12

<DllImport("Shell32", CharSet:=CharSet.Auto, SetLastError:=True)> _
    Public Shared Function ShellExecuteEx(ByRef lpExecInfo As SHELLEXECUTEINFO) As Boolean
    End Function

Dim sei As New SHELLEXECUTEINFO
sei.cbSize = Marshal.SizeOf(sei)
sei.lpVerb = "properties"
sei.lpFile = "FilePath"
sei.nShow = SW_SHOW
sei.fMask = SEE_MASK_INVOKEIDLIST
If Not ShellExecuteEx(sei) Then
   Dim ex As New System.ComponentModel.Win32Exception(System.Runtime.InteropServices.Marshal.GetLastWin32Error())
       MessageBox.Show(ex.Message, Me.TITLE, MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
End If

Verbs for lpVerb:

"open"        - see MSDN
"openas"    - Opens dialog when no program is associated to the extension
"opennew"    - see MSDN
"edit"        - see MSDN    
"explore"    - see MSDN
"properties"    - see MSDN
"copy"        - see MSDN
"cut"        - see MSDN
"paste"    - see MSDN
"pastelink"    - pastes a shortcut
"delete"    - see MSDN
"print"    - see MSDN
"printto"    - see MSDN
"find"        - see MSDN

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