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How to open file with Process.Start if there is no associated program for the file type?

When I want to open an .ico file using Process.Start it throws an error System.ComponentModel.Win32Exception and this is because there is no default program to open that file. I need to show the window to select the default program instead of throwing exception. How can I do that?
private void btnOpenFile_Click(object sender, EventArgs e)
{
Process.Start(txtSavedAs.Text);
}

What you want to do is pinvoke the AssocQueryString API. Documentation here.
I use that API to get a command string associated with a shell verb. So, for example, if I use the .txt extension, it would return:
C:\Windows\system32\NOTEPAD.EXE %1
Now we know that shell knows what program to execute and how to pass in the command-line argument for that specific extension.
So, if there is a "Command" associated with that extension, it is safe to assume shell will know how to execute that type of file; Hence we should be able to use ShellExecute normally.
If there is no "Command" associated with that file extension, we will show the "openas" dialog allowing the user to pick the application they want to open the file.
Here is a class I put together to do that work:
AppAssociation.cs
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
public static class AppAssociation
{
private static class Win32Native
{
public const int ASSOCF_NONE = 0;
public const int ASSOCSTR_COMMAND = 1;
[DllImport("shlwapi.dll", CharSet = CharSet.Unicode,
EntryPoint = "AssocQueryStringW")]
public static extern uint AssocQueryString(int flags, int str,
string pszAssoc, string pszExtra, StringBuilder pszOut, ref uint pcchOut);
}
public static Process StartProcessForFile(FileInfo file)
{
var command = GetCommandForFileExtention(file.Extension);
return Process.Start(new ProcessStartInfo()
{
WindowStyle = ProcessWindowStyle.Normal,
FileName = file.FullName,
Verb = string.IsNullOrEmpty(command) ? "openas" : null,
UseShellExecute = true,
ErrorDialog = true
});
}
private static string GetCommandForFileExtention(string ext)
{
// query length of the buffer we need
uint length = 0;
if (Win32Native.AssocQueryString(Win32Native.ASSOCF_NONE,
Win32Native.ASSOCSTR_COMMAND, ext, null, null, ref length) == 1)
{
// build the buffer
var sb = new StringBuilder((int)length);
// ask for the actual command string with the right-sized buffer
if (Win32Native.AssocQueryString(Win32Native.ASSOCF_NONE,
Win32Native.ASSOCSTR_COMMAND, ext, null, sb, ref length) == 0)
{
return sb.ToString();
}
}
return null;
}
}
You would call this like so:
AppAssociation.StartProcessForFile(new FileInfo(#"c:\MyFiles\TheFile.txt"));

Dot net core C# open photo viewer with Process Class

I am going to open the photo viewer using .net core and this is my code
using System.Diagnostics;
namespace TestProcessForOpenPhoto
{
class Program
{
static void Main(string[] args)
{
var photoViewer = new Process();
photoViewer.StartInfo.FileName = #"C:\Program Files\Windows Photo Viewer\PhotoViewer.dll";
photoViewer.StartInfo.Arguments = #" C:\Users\XXXXX\Desktop\TestImage\abc.jpg";
photoViewer.StartInfo.UseShellExecute = false;
photoViewer.Start();
}
}
}
and I got this error message
System.ComponentModel.Win32Exception: 'The specified executable is not a valid application for this OS platform.'
Can anyone help me to fix this bug, thanks

After researching this I noticed folks using rundll32.exe to execute an export from PhotoViewer.dll to display a picture using Microsoft Photo Viewer application. So I think that's what OP was trying to do, they just forgot to use the rundll32.exe application.
So I thought I'd take a crack at this and not use the rundll32.exe and just call the export directly. I debugged it with x86dbg and saw that it's passing in 4 parameters: pointer, pointer, pointer (to wchar_t*), int. I don't know what the parameters do, so I just set them to NULL and made sure to pass in the path to the picture as the 3rd and it seems to work.
So this will do what you want it to do. I know that hard-coding system paths is bad practice, but maybe someone who has more time can make this more dynamic.
private static class WindowsPhotoViewer
{
private const string FilePath32 = #"c:\program files (x86)\Windows Photo Viewer\PhotoViewer.dll";
private const string FilePath64 = #"c:\program files\Windows Photo Viewer\PhotoViewer.dll";
[DllImport(FilePath32, CharSet = CharSet.Unicode, EntryPoint = "ImageView_FullscreenW")]
private static extern void ImageView_Fullscreen32(
IntPtr unknown1, IntPtr unknown2, string path, int unknown3);
[DllImport(FilePath64, CharSet = CharSet.Unicode, EntryPoint = "ImageView_FullscreenW")]
private static extern void ImageView_Fullscreen64(
IntPtr unknown1, IntPtr unknown2, string path, int unknown3);
public static bool ShowImage(FileInfo imageFile)
{
if ((IntPtr.Size == 8) && File.Exists(FilePath64) && imageFile.Exists)
{
ImageView_Fullscreen64(IntPtr.Zero, IntPtr.Zero, imageFile.FullName, 0);
return true;
}
else if ((IntPtr.Size == 4) && File.Exists(FilePath32) && imageFile.Exists)
{
ImageView_Fullscreen32(IntPtr.Zero, IntPtr.Zero, imageFile.FullName, 0);
return true;
}
return false;
}
}
Then you can call it as so:
if(!WindowsPhotoViewer.ShowImage(new FileInfo(#"c:\users\andy\desktop\test.jpg")))
{
Console.WriteLine("Failed to show image");
}

WPF application file association: DefaultIcon is not working

I want to association ".abc" file to my WPF application.
I add the association using this code:
public class FileAssociation
{
static RegistryKey Root
{
get
{
return Registry.CurrentUser;
}
}
// Associate file extension with progID, description, icon and application
public static void Associate(string extension,
string progID, string description, string application)
{
Require.NotNullOrEmpty(extension, "extension");
Require.NotNullOrEmpty(progID, "progID");
Require.NotNullOrEmpty(application, "application");
Require.NotNullOrEmpty(description, "description");
Root.CreateSubKey(extension).SetValue("", progID);
using (var key = Root.CreateSubKey(progID))
{
key.SetValue("", description);
key.CreateSubKey("DefaultIcon").SetValue("", ToShortPathName(application).Quote() + ",0");
key.CreateSubKey(#"Shell\Open\Command").SetValue("", ToShortPathName(application).Quote() + " \"%1\"");
// Tell explorer the file association has been changed
SHChangeNotify(0x08000000, 0x0000, IntPtr.Zero, IntPtr.Zero);
}
}
// Return true if extension already associated in registry
public static bool IsAssociated(string extension)
{
return (Root.OpenSubKey(extension, false) != null);
}
[DllImport("shell32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern void SHChangeNotify(uint wEventId, uint uFlags, IntPtr dwItem1, IntPtr dwItem2);
[DllImport("Kernel32.dll")]
private static extern uint GetShortPathName(string lpszLongPath,
[Out] StringBuilder lpszShortPath, uint cchBuffer);
// Return short path format of a file name
private static string ToShortPathName(string longName)
{
StringBuilder s = new StringBuilder(1000);
uint iSize = (uint)s.Capacity;
uint iRet = GetShortPathName(longName, s, iSize);
return s.ToString();
}
}
Note: The Quote() extension method is used just to make string abc to "abc".
Now the file association works fine! I can double click the ".abc" files to open my WPF app.
But the DefaultIcon is not working. The DefaultIcon Registery key is set to "D:\path\to\MyWPFApp.exe",0. The application icon of my WPF app is set to an icon in the properties page (I can see that the icon of MyWPFApp.exe is already changed). What's wrong? Thanks!
BTW: I'm using .NET 4 in Windows 8

You don't need the DefaultIcon entry. The first icon is used by default.
remove it and it should work ^^
If I remove the ToShortPathName (long name is ok with quotes) and
change the Root property returns Registry.ClassesRoot the code works here.

How to add an icon to an existing exe file (without an icon by default)?

When I was searching on Google I found a useful class which let us change the icon of any .exe file using the following line of code :
WindowsFormsApplication1.IconInjector.InjectIcon("myfile.exe", "myicon.ico", 200, 1);
Where 200 and 1 are respectively icon GroupID and icon BaseID which I can determine using Resource Hacker. In this case the file's icon changes successfully without corrupting the file.
So i planned to use this class on my program which is a SFX / Software protector, the output file always hasn't an icon, all what I can see on Resource hacker is the below :
i can't see icon group id nor the base id, anyway, (I don't know what to put instead of 200 and 1 in this case) So I tried to change the icon using the same line of code mentioned above, I used the following line of code (same as above):
WindowsFormsApplication1.IconInjector.InjectIcon("myfile.exe", "myicon.ico", 200, 1);
The file icon was successfully changed but the file doesn't work anymore!
When I tried to reopen the file using ResourceHacker, I found the below:
It seems that the icon resources were successfully added, but i can't figure out why the file doesn't work anymore, it seems that is corrupted.
Any help would be appreciated.
Note : I tried using this class with unprotected file and it works like a charm!
The class I am using is the below:
// IconInjector.cs
using System;
using System.Runtime.InteropServices;
using System.Diagnostics;
namespace WindowsFormsApplication1
{
/// <summary>
/// IconInjectorクラスの定義
/// </summary>
public class IconInjector
{
[DllImport("kernel32.dll", SetLastError = true)]
//static extern bool UpdateResource(IntPtr hUpdate, string lpType, string lpName, ushort wLanguage, IntPtr lpData, uint cbData);
static extern int UpdateResource(IntPtr hUpdate, uint lpType, uint lpName, ushort wLanguage, byte[] lpData, uint cbData);
[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr BeginUpdateResource(string pFileName,
[MarshalAs(UnmanagedType.Bool)]bool bDeleteExistingResources);
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool EndUpdateResource(IntPtr hUpdate, bool fDiscard);
/// <summary>
/// アプリケーションのメイン エントリ ポイントです。
/// </summary>
[STAThread]
public static void InjectIcon(string execFileName, string iconFileName, uint iconGroupID, uint iconBaseID)
{
const uint RT_ICON = 3;
const uint RT_GROUP_ICON = 14;
// アイコンファイルの読み込み
IconFile iconFile = new IconFile();
iconFile.Load(iconFileName);
// リソースの更新開始
IntPtr hUpdate = BeginUpdateResource(execFileName, false);
Debug.Assert(hUpdate != IntPtr.Zero);
// RT_GROUP_ICON 書き込み
byte[] data = iconFile.CreateIconGroupData(iconBaseID);
UpdateResource(hUpdate, RT_GROUP_ICON, iconGroupID, 0, data, (uint)data.Length);
// RT_ICON書き込み
for (int i = 0; i < iconFile.GetImageCount(); i++)
{
byte[] image = iconFile.GetImageData(i);
UpdateResource(hUpdate, RT_ICON, (uint)(iconBaseID + i), 0, image, (uint)image.Length);
}
// リソースの更新終了
EndUpdateResource(hUpdate, false);
}
}
}
Any help or suggestion on adding the icon to the protected file without corrupting it?

It sounds like the protection application is verifying that the contents of the file haven't been tampered with. Injecting an icon is definitely a form of tampering, and unless the protection software is updated to ignore it, it will always fail. Alternatively if you own the protection software you could update it to not strip the icons.

I just experienced the same issue with a 7zip Self-Extractor exe.
Updating the icon of the 7zS.sfx (instead of the exe) before creating the Self-Extractor exe does the trick and the exe is not corrupted.

Your application's icon can be added to this executable with a tool like Resource Hacker.
and visit http://georezo.net/jparis/MI_Enviro/Icons/adding_w_RH.htm

How to open text in Notepad from .NET?

When I click a button on a Windows Forms form, I would like to open a Notepad window containing the text from a TextBox control on the form.
How can I do that?

You don't need to create file with this string. You can use P/Invoke to solve your problem.
Usage of NotepadHelper class:
NotepadHelper.ShowMessage("My message...", "My Title");
NotepadHelper class code:
using System;
using System.Runtime.InteropServices;
using System.Diagnostics;
namespace Notepad
{
public static class NotepadHelper
{
[DllImport("user32.dll", EntryPoint = "SetWindowText")]
private static extern int SetWindowText(IntPtr hWnd, string text);
[DllImport("user32.dll", EntryPoint = "FindWindowEx")]
private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
[DllImport("User32.dll", EntryPoint = "SendMessage")]
private static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, string lParam);
public static void ShowMessage(string message = null, string title = null)
{
Process notepad = Process.Start(new ProcessStartInfo("notepad.exe"));
if (notepad != null)
{
notepad.WaitForInputIdle();
if (!string.IsNullOrEmpty(title))
SetWindowText(notepad.MainWindowHandle, title);
if (!string.IsNullOrEmpty(message))
{
IntPtr child = FindWindowEx(notepad.MainWindowHandle, new IntPtr(0), "Edit", null);
SendMessage(child, 0x000C, 0, message);
}
}
}
}
}
References (pinvoke.net and msdn.microsoft.com):
SetWindowText: pinvoke | msdn
FindWindowEx: pinvoke | msdn
SendMessage: pinvoke | msdn

Try this out:
System.IO.File.WriteAllText(#"C:\test.txt", textBox.Text);
System.Diagnostics.Process.Start(#"C:\test.txt");

Save the file to disk using File.WriteAllText:
File.WriteAllText("path to text file", myTextBox.Text);
Then use Process.Start to open it in notepad:
Process.Start("path to notepad.exe", "path to text file");

For non ASCII user.
[DllImport("User32.dll", EntryPoint = "SendMessage", CharSet = CharSet.Unicode)]
private static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, string lParam);
Based on #Peter Mortensen answer
Add CharSet = CharSet.Unicode to the attribute for supporting Unicode characters

I was using the NotepadHelper solution until I discovered it doesn't work on Windows 11. Writing the file to disk and starting with the default text editor seems to be the best solution. This has already been posted, but I discovered you need to pass UseShellExecute=true.
System.IO.File.WriteAllText(path, value);
System.Diagnostics.ProcessStartInfo psi = new() { FileName = path, UseShellExecute = true };
System.Diagnostics.Process.Start(psi);
I write to the System.IO.Path.GetTempPath() folder and run a cleanup when the application exits - searching for a unique prefix pattern for file names used by my app. Something like this:
string pattern = TempFilePrefix + "*.txt";
foreach (string f in Directory.EnumerateFiles(Path.GetTempPath(), pattern))
{
File.Delete(f);
}