Change keyboard layout from C# code with .NET 4.5.2

Question

I am coding away on my plugin for SDL Trados Studio.

The last part of the plugin requires some automation that is not exposed by the APIs at all, so all I have (hold on to something) is to automate the default keyboard shortcuts.

I have the code working perfectly for the English keyboard layout (and Hungarian, too!), but it of course does not work for Greek, Russian and so forth.

I have been searching for the solution but I was not able to find it until now, not on the web nor on SO, such as this post: Change keyboard layouts through code c#

I need to change the keyboard layout to English so it can take the correct shortcuts (and other character strings). Then I need to switch it back to what it was before. I am working with a very limited API, so I only have SendKeys at my disposal.

Here is the working code:

//Save the document
SendKeys.SendWait("^s");
//Open files view
SendKeys.SendWait("%v");

SendKeys.SendWait("i");
SendKeys.SendWait("1");
Application.DoEvents();

//get url and credentials from a custom input form
string[] psw = UploadData.GetPassword(
    Settings.GetValue("Upload", "Uri", ""), 
    Vars.wsUsername == null ? Settings.GetValue("Upload", "User", "") : Vars.wsUsername, 
    Vars.wsPassword == null ? "" : Vars.wsPassword
    );
Application.DoEvents();

if (psw != null)
{
    try
    {
        //start upload
        SendKeys.SendWait("%h");
        SendKeys.Send("r");

        //select all files
        SendKeys.Send("%a");
        SendKeys.Send("%n");
        //enter login url
        SendKeys.Send("%l");
        SendKeys.Send("{TAB}");
        SendKeys.Send(psw[0]);
        SendKeys.Send("{TAB}");
        SendKeys.Send("{ENTER}");

        //enter username
        SendKeys.Send("%l");
        SendKeys.Send("+{END}");
        SendKeys.Send(psw[1]);
        //enter credentials
        SendKeys.Send("%p");
        SendKeys.Send(SendEscape(psw[2]));
        SendKeys.Send("{ENTER}");
        //start upload
        SendKeys.SendWait("%f");
    }
    catch (Exception)
    {
        MessageBox.Show("Cannot do automatic upload, please use the default method of Trados Studio.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
    }
    finally
    {
        //switch back to editor view
        SendKeys.SendWait("%vd");
    }
}

So the questions I have:

1. Can somebody help me with a code to actually store the current keyboard layout and switch to English, then switch it back at the end?

2. Is there a simpler solution? I tried to look at the native methods but it is too high for me, so I would really appreciate any help to convert my code into native if that is the way to go instead of switching the keyboard layout. Any suggestions?

Answer 1

Switching the keyboard layout requires some P/Invoke; you´ll need at least the following Windows functions to get it working: LoadKeyboardLayout, GetKeyboardLayout and ActivateKeyboardLayout. The following import declarations worked for me...

[DllImport("user32.dll", 
    CallingConvention = CallingConvention.StdCall, 
    CharSet = CharSet.Unicode, 
    EntryPoint = "LoadKeyboardLayout", 
    SetLastError = true, 
    ThrowOnUnmappableChar = false)]
static extern uint LoadKeyboardLayout(
    StringBuilder pwszKLID, 
    uint flags);

[DllImport("user32.dll", 
    CallingConvention = CallingConvention.StdCall,
    CharSet = CharSet.Unicode, 
    EntryPoint = "GetKeyboardLayout", 
    SetLastError = true, 
    ThrowOnUnmappableChar = false)]
static extern uint GetKeyboardLayout(
    uint idThread);

[DllImport("user32.dll", 
    CallingConvention = CallingConvention.StdCall, 
    CharSet = CharSet.Unicode, 
    EntryPoint = "ActivateKeyboardLayout", 
    SetLastError = true, 
    ThrowOnUnmappableChar = false)]
static extern uint ActivateKeyboardLayout(
    uint hkl,
    uint Flags);

static class KeyboardLayoutFlags
{
    public const uint KLF_ACTIVATE = 0x00000001;
    public const uint KLF_SETFORPROCESS = 0x00000100;
}

Whenever I have to use native API methods I try to encapsulate them in a class that hides their declaration from the rest of the project´s codebase. So, I came up with a class called KeyboardLayout; that class can load and activate a layout by a given CultureInfo, which comes in handy...

internal sealed class KeyboardLayout
{
    ...

    private readonly uint hkl;

    private KeyboardLayout(CultureInfo cultureInfo)
    {
        string layoutName = cultureInfo.LCID.ToString("x8");

        var pwszKlid = new StringBuilder(layoutName);
        this.hkl = LoadKeyboardLayout(pwszKlid, KeyboardLayoutFlags.KLF_ACTIVATE);
    }

    private KeyboardLayout(uint hkl)
    {
        this.hkl = hkl;
    }

    public uint Handle
    {
        get
        {
            return this.hkl;
        }
    }

    public static KeyboardLayout GetCurrent()
    {
        uint hkl = GetKeyboardLayout((uint)Thread.CurrentThread.ManagedThreadId);
        return new KeyboardLayout(hkl);
    }

    public static KeyboardLayout Load(CultureInfo culture)
    {
        return new KeyboardLayout(culture);
    }

    public void Activate()
    {
        ActivateKeyboardLayout(this.hkl, KeyboardLayoutFlags.KLF_SETFORPROCESS);
    }
}

If you only need to have the layout be active for a short while - and you want make sure to properly restore the layout when done, you could write some kind of a scope type using the IDiposable interface. For instance...

class KeyboardLayoutScope : IDiposable
{
    private readonly KeyboardLayout currentLayout;

    public KeyboardLayoutScope(CultureInfo culture)
    {
        this.currentLayout = KeyboardLayout.GetCurrent();
        var layout = KeyboardLayout.Load(culture);
        layout.Activate();
    }

    public void Dispose()
    {
        this.currentLayout.Activate();
    }
}

Than you can use it like this...

const int English = 1033;
using (new KeyboardLayoutScope(CultureInfo.GetCultureInfo(English))
{
    // the layout will be valid within this using-block
}

You should know that in newer versions of Windows (beginning in Windows 8) the keyboard layout cannot be set for a certain process anymore, instead it is set globally for the entire system - and the layout can also be changed by other applications, or by the user (using the Win + Spacebar shortcut).

I would also recommend to not use SendKeys (or its native counterpart SendInput) since it simulates keyboard input which will be routed to the active/focused window. Using the SendMessage function instead is suitable, but you might want combine that with functionality that can properly determine the target window; but to explain such technique would go beyond the scope of the this question and answer. This answer here illustrates a possible solution: How to send keystrokes to a window?