Global keyboard capture in C application

Question

I want to capture a keyboard shortcut in my application and trigger a dialog to appear if the user presses a keyboard combo even outside of the app  Similar to Google Desktop Search s Ctrl  Ctrl to bring up the search dialog   I have tried using some keyboard hook modules out there that basically use Win32 interop to get this effect but each implementation I ve tried ties down the keyboard to some extent to where you start getting weird behaviors when the application is doing something intensive  Such as loading a large amount of data  this would cause the keyboard and mouse to lockup   I m looking for a lightweight solution that would allow this to be done without tying down the keyboard and mouse

User · Answer

If a global hotkey would suffice  then RegisterHotKey would do the trick

User · Answer

Stephen Toub wrote a great article on implementing global keyboard hooks in C   using System  using System Diagnostics  using System Windows Forms  using System Runtime InteropServices   class InterceptKeys       private const int WH KEYBOARD LL   13      private const int WM KEYDOWN   0x0100      private static LowLevelKeyboardProc  proc   HookCallback      private static IntPtr  hookID   IntPtr Zero       public static void Main                  hookID   SetHook  proc           Application Run            UnhookWindowsHookEx  hookID              private static IntPtr SetHook LowLevelKeyboardProc proc                using  Process curProcess   Process GetCurrentProcess            using  ProcessModule curModule   curProcess MainModule                        return SetWindowsHookEx WH KEYBOARD LL  proc                  GetModuleHandle curModule ModuleName   0                        private delegate IntPtr LowLevelKeyboardProc          int nCode  IntPtr wParam  IntPtr lParam        private static IntPtr HookCallback          int nCode  IntPtr wParam  IntPtr lParam                if  nCode  gt   0  amp  amp  wParam     IntPtr WM KEYDOWN                        int vkCode   Marshal ReadInt32 lParam               Console WriteLine  Keys vkCode                     return CallNextHookEx  hookID  nCode  wParam  lParam               DllImport  quot user32 dll quot   CharSet   CharSet Auto  SetLastError   true       private static extern IntPtr SetWindowsHookEx int idHook          LowLevelKeyboardProc lpfn  IntPtr hMod  uint dwThreadId         DllImport  quot user32 dll quot   CharSet   CharSet Auto  SetLastError   true        return  MarshalAs UnmanagedType Bool       private static extern bool UnhookWindowsHookEx IntPtr hhk         DllImport  quot user32 dll quot   CharSet   CharSet Auto  SetLastError   true       private static extern IntPtr CallNextHookEx IntPtr hhk  int nCode          IntPtr wParam  IntPtr lParam         DllImport  quot kernel32 dll quot   CharSet   CharSet Auto  SetLastError   true       private static extern IntPtr GetModuleHandle string lpModuleName

User · Answer

As requested by dube I m posting my modified version of Siarhei Kuchuk s answer  If you want to check my changes search for    EDT  I ve commented most of it   The Setup  class GlobalKeyboardHookEventArgs   HandledEventArgs       public GlobalKeyboardHook KeyboardState KeyboardState   get  private set        public GlobalKeyboardHook LowLevelKeyboardInputEvent KeyboardData   get  private set         public GlobalKeyboardHookEventArgs          GlobalKeyboardHook LowLevelKeyboardInputEvent keyboardData          GlobalKeyboardHook KeyboardState keyboardState                KeyboardData   keyboardData          KeyboardState   keyboardState             Based on https   gist github com Stasonix class GlobalKeyboardHook   IDisposable       public event EventHandler lt GlobalKeyboardHookEventArgs gt  KeyboardPressed          EDT  Added an optional parameter  registeredKeys  that accepts keys to restict        the logging mechanism           lt summary gt                    lt  summary gt           lt param name  registeredKeys  gt Keys that should trigger logging  Pass null for full logging  lt  param gt      public GlobalKeyboardHook Keys   registeredKeys   null                RegisteredKeys   registeredKeys           windowsHookHandle   IntPtr Zero           user32LibraryHandle   IntPtr Zero           hookProc   LowLevelKeyboardProc     we must keep alive  hookProc  because GC is not aware about SetWindowsHookEx behaviour            user32LibraryHandle   LoadLibrary  User32            if   user32LibraryHandle    IntPtr Zero                        int errorCode   Marshal GetLastWin32Error                throw new Win32Exception errorCode    Failed to load library  User32 dll   Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                            windowsHookHandle   SetWindowsHookEx WH KEYBOARD LL   hookProc   user32LibraryHandle  0           if   windowsHookHandle    IntPtr Zero                        int errorCode   Marshal GetLastWin32Error                throw new Win32Exception errorCode    Failed to adjust keyboard hooks for   Process GetCurrentProcess   ProcessName    Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                           protected virtual void Dispose bool disposing                if  disposing                           because we can unhook only in the same thread  not in garbage collector thread             if   windowsHookHandle    IntPtr Zero                                if   UnhookWindowsHookEx  windowsHookHandle                                         int errorCode   Marshal GetLastWin32Error                        throw new Win32Exception errorCode    Failed to remove keyboard hooks for   Process GetCurrentProcess   ProcessName    Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                         windowsHookHandle   IntPtr Zero                      ReSharper disable once DelegateSubtraction                  hookProc -  LowLevelKeyboardProc                                   if   user32LibraryHandle    IntPtr Zero                        if   FreeLibrary  user32LibraryHandle      reduces reference to library by 1                                int errorCode   Marshal GetLastWin32Error                    throw new Win32Exception errorCode    Failed to unload library  User32 dll   Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                 user32LibraryHandle   IntPtr Zero                        GlobalKeyboardHook                 Dispose false              public void Dispose                 Dispose true           GC SuppressFinalize this              private IntPtr  windowsHookHandle      private IntPtr  user32LibraryHandle      private HookProc  hookProc       delegate IntPtr HookProc int nCode  IntPtr wParam  IntPtr lParam         DllImport  kernel32 dll        private static extern IntPtr LoadLibrary string lpFileName         DllImport  kernel32 dll   CharSet   CharSet Auto       private static extern bool FreeLibrary IntPtr hModule             lt summary gt          The SetWindowsHookEx function installs an application-defined hook procedure into a hook chain          You would install a hook procedure to monitor the system for certain types of events  These events are         associated either with a specific thread or with all threads in the same desktop as the calling thread           lt  summary gt           lt param name  idHook  gt hook type lt  param gt           lt param name  lpfn  gt hook procedure lt  param gt           lt param name  hMod  gt handle to application instance lt  param gt           lt param name  dwThreadId  gt thread identifier lt  param gt           lt returns gt If the function succeeds  the return value is the handle to the hook procedure  lt  returns gt       DllImport  USER32   SetLastError   true       static extern IntPtr SetWindowsHookEx int idHook  HookProc lpfn  IntPtr hMod  int dwThreadId             lt summary gt          The UnhookWindowsHookEx function removes a hook procedure installed in a hook chain by the SetWindowsHookEx function           lt  summary gt           lt param name  hhk  gt handle to hook procedure lt  param gt           lt returns gt If the function succeeds  the return value is true  lt  returns gt       DllImport  USER32   SetLastError   true       public static extern bool UnhookWindowsHookEx IntPtr hHook             lt summary gt          The CallNextHookEx function passes the hook information to the next hook procedure in the current hook chain          A hook procedure can call this function either before or after processing the hook information           lt  summary gt           lt param name  hHook  gt handle to current hook lt  param gt           lt param name  code  gt hook code passed to hook procedure lt  param gt           lt param name  wParam  gt value passed to hook procedure lt  param gt           lt param name  lParam  gt value passed to hook procedure lt  param gt           lt returns gt If the function succeeds  the return value is true  lt  returns gt       DllImport  USER32   SetLastError   true       static extern IntPtr CallNextHookEx IntPtr hHook  int code  IntPtr wParam  IntPtr lParam         StructLayout LayoutKind Sequential       public struct LowLevelKeyboardInputEvent                    lt summary gt              A virtual-key code  The code must be a value in the range 1 to 254               lt  summary gt          public int VirtualCode              EDT  added a conversion from VirtualCode to Keys               lt summary gt              The VirtualCode converted to typeof Keys  for higher usability               lt  summary gt          public Keys Key   get   return  Keys VirtualCode                    lt summary gt              A hardware scan code for the key                lt  summary gt          public int HardwareScanCode                lt summary gt              The extended-key flag  event-injected Flags  context code  and transition-state flag  This member is specified as follows  An application can use the following values to test the keystroke Flags  Testing LLKHF INJECTED  bit 4  will tell you whether the event was injected  If it was  then testing LLKHF LOWER IL INJECTED  bit 1  will tell you whether or not the event was injected from a process running at lower integrity level               lt  summary gt          public int Flags                lt summary gt              The time stamp stamp for this message  equivalent to what GetMessageTime would return for this message               lt  summary gt          public int TimeStamp                lt summary gt              Additional information associated with the message                lt  summary gt          public IntPtr AdditionalInformation             public const int WH KEYBOARD LL   13        const int HC ACTION   0       public enum KeyboardState               KeyDown   0x0100          KeyUp   0x0101          SysKeyDown   0x0104          SysKeyUp   0x0105               EDT  Replaced VkSnapshot int  with RegisteredKeys Keys        public static Keys   RegisteredKeys      const int KfAltdown   0x2000      public const int LlkhfAltdown    KfAltdown  gt  gt  8        public IntPtr LowLevelKeyboardProc int nCode  IntPtr wParam  IntPtr lParam                bool fEatKeyStroke   false           var wparamTyped   wParam ToInt32            if  Enum IsDefined typeof KeyboardState   wparamTyped                         object o   Marshal PtrToStructure lParam  typeof LowLevelKeyboardInputEvent                LowLevelKeyboardInputEvent p    LowLevelKeyboardInputEvent o               var eventArguments   new GlobalKeyboardHookEventArgs p   KeyboardState wparamTyped                   EDT  Removed the comparison-logic from the usage-area so the user does not need to mess around with it                 Either the incoming key has to be part of RegisteredKeys  see constructor on top  or RegisterdKeys                has to be null for the event to get fired              var key    Keys p VirtualCode              if  RegisteredKeys    null    RegisteredKeys Contains key                                 EventHandler lt GlobalKeyboardHookEventArgs gt  handler   KeyboardPressed                  handler  Invoke this  eventArguments                    fEatKeyStroke   eventArguments Handled                                   return fEatKeyStroke    IntPtr 1   CallNextHookEx IntPtr Zero  nCode  wParam  lParam             The Usage differences can be seen here  public partial class Form1   Form       public Form1                 InitializeComponent               private GlobalKeyboardHook  globalKeyboardHook       private void buttonHook Click object sender  EventArgs e                   Hooks only into specified Keys  here  A  and  B             globalKeyboardHook   new GlobalKeyboardHook new Keys     Keys A  Keys B                 Hooks into all keys           globalKeyboardHook   new GlobalKeyboardHook             globalKeyboardHook KeyboardPressed    OnKeyPressed             private void OnKeyPressed object sender  GlobalKeyboardHookEventArgs e                   EDT  No need to filter for VkSnapshot anymore  This now gets handled            through the constructor of GlobalKeyboardHook               if  e KeyboardState    GlobalKeyboardHook KeyboardState KeyDown                           Now you can access both  the key and virtual code             Keys loggedKey   e KeyboardData Key              int loggedVkCode   e KeyboardData VirtualCode                      Thanks to Siarhei Kuchuk for his post  Even tho I ve simplified the usage this initial code was very useful for me

User · Answer

Here s my code that works   using System  using System ComponentModel  using System Diagnostics  using System Runtime InteropServices   namespace SnagFree TrayApp Core       class GlobalKeyboardHookEventArgs   HandledEventArgs               public GlobalKeyboardHook KeyboardState KeyboardState   get  private set            public GlobalKeyboardHook LowLevelKeyboardInputEvent KeyboardData   get  private set             public GlobalKeyboardHookEventArgs              GlobalKeyboardHook LowLevelKeyboardInputEvent keyboardData              GlobalKeyboardHook KeyboardState keyboardState                        KeyboardData   keyboardData              KeyboardState   keyboardState                         Based on https   gist github com Stasonix     class GlobalKeyboardHook   IDisposable               public event EventHandler lt GlobalKeyboardHookEventArgs gt  KeyboardPressed           public GlobalKeyboardHook                          windowsHookHandle   IntPtr Zero               user32LibraryHandle   IntPtr Zero               hookProc   LowLevelKeyboardProc     we must keep alive  hookProc  because GC is not aware about SetWindowsHookEx behaviour                user32LibraryHandle   LoadLibrary  User32                if   user32LibraryHandle    IntPtr Zero                                int errorCode   Marshal GetLastWin32Error                    throw new Win32Exception errorCode    Failed to load library  User32 dll   Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                    windowsHookHandle   SetWindowsHookEx WH KEYBOARD LL   hookProc   user32LibraryHandle  0               if   windowsHookHandle    IntPtr Zero                                int errorCode   Marshal GetLastWin32Error                    throw new Win32Exception errorCode    Failed to adjust keyboard hooks for   Process GetCurrentProcess   ProcessName    Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                       protected virtual void Dispose bool disposing                        if  disposing                                   because we can unhook only in the same thread  not in garbage collector thread                 if   windowsHookHandle    IntPtr Zero                                        if   UnhookWindowsHookEx  windowsHookHandle                                                 int errorCode   Marshal GetLastWin32Error                            throw new Win32Exception errorCode    Failed to remove keyboard hooks for   Process GetCurrentProcess   ProcessName    Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                                 windowsHookHandle   IntPtr Zero                          ReSharper disable once DelegateSubtraction                      hookProc -  LowLevelKeyboardProc                                               if   user32LibraryHandle    IntPtr Zero                                if   FreeLibrary  user32LibraryHandle      reduces reference to library by 1                                        int errorCode   Marshal GetLastWin32Error                        throw new Win32Exception errorCode    Failed to unload library  User32 dll   Error  errorCode    new Win32Exception Marshal GetLastWin32Error    Message                                         user32LibraryHandle   IntPtr Zero                                    GlobalKeyboardHook                         Dispose false                      public void Dispose                         Dispose true               GC SuppressFinalize this                      private IntPtr  windowsHookHandle          private IntPtr  user32LibraryHandle          private HookProc  hookProc           delegate IntPtr HookProc int nCode  IntPtr wParam  IntPtr lParam             DllImport  kernel32 dll            private static extern IntPtr LoadLibrary string lpFileName             DllImport  kernel32 dll   CharSet   CharSet Auto           private static extern bool FreeLibrary IntPtr hModule                 lt summary gt              The SetWindowsHookEx function installs an application-defined hook procedure into a hook chain              You would install a hook procedure to monitor the system for certain types of events  These events are             associated either with a specific thread or with all threads in the same desktop as the calling thread               lt  summary gt               lt param name  idHook  gt hook type lt  param gt               lt param name  lpfn  gt hook procedure lt  param gt               lt param name  hMod  gt handle to application instance lt  param gt               lt param name  dwThreadId  gt thread identifier lt  param gt               lt returns gt If the function succeeds  the return value is the handle to the hook procedure  lt  returns gt           DllImport  USER32   SetLastError   true           static extern IntPtr SetWindowsHookEx int idHook  HookProc lpfn  IntPtr hMod  int dwThreadId                 lt summary gt              The UnhookWindowsHookEx function removes a hook procedure installed in a hook chain by the SetWindowsHookEx function               lt  summary gt               lt param name  hhk  gt handle to hook procedure lt  param gt               lt returns gt If the function succeeds  the return value is true  lt  returns gt           DllImport  USER32   SetLastError   true           public static extern bool UnhookWindowsHookEx IntPtr hHook                 lt summary gt              The CallNextHookEx function passes the hook information to the next hook procedure in the current hook chain              A hook procedure can call this function either before or after processing the hook information               lt  summary gt               lt param name  hHook  gt handle to current hook lt  param gt               lt param name  code  gt hook code passed to hook procedure lt  param gt               lt param name  wParam  gt value passed to hook procedure lt  param gt               lt param name  lParam  gt value passed to hook procedure lt  param gt               lt returns gt If the function succeeds  the return value is true  lt  returns gt           DllImport  USER32   SetLastError   true           static extern IntPtr CallNextHookEx IntPtr hHook  int code  IntPtr wParam  IntPtr lParam             StructLayout LayoutKind Sequential           public struct LowLevelKeyboardInputEvent                            lt summary gt                  A virtual-key code  The code must be a value in the range 1 to 254                   lt  summary gt              public int VirtualCode                    lt summary gt                  A hardware scan code for the key                    lt  summary gt              public int HardwareScanCode                    lt summary gt                  The extended-key flag  event-injected Flags  context code  and transition-state flag  This member is specified as follows  An application can use the following values to test the keystroke Flags  Testing LLKHF INJECTED  bit 4  will tell you whether the event was injected  If it was  then testing LLKHF LOWER IL INJECTED  bit 1  will tell you whether or not the event was injected from a process running at lower integrity level                   lt  summary gt              public int Flags                    lt summary gt                  The time stamp stamp for this message  equivalent to what GetMessageTime would return for this message                   lt  summary gt              public int TimeStamp                    lt summary gt                  Additional information associated with the message                    lt  summary gt              public IntPtr AdditionalInformation                     public const int WH KEYBOARD LL   13            const int HC ACTION   0           public enum KeyboardState                       KeyDown   0x0100              KeyUp   0x0101              SysKeyDown   0x0104              SysKeyUp   0x0105                    public const int VkSnapshot   0x2c            const int VkLwin   0x5b            const int VkRwin   0x5c            const int VkTab   0x09            const int VkEscape   0x18            const int VkControl   0x11          const int KfAltdown   0x2000          public const int LlkhfAltdown    KfAltdown  gt  gt  8            public IntPtr LowLevelKeyboardProc int nCode  IntPtr wParam  IntPtr lParam                        bool fEatKeyStroke   false               var wparamTyped   wParam ToInt32                if  Enum IsDefined typeof KeyboardState   wparamTyped                                 object o   Marshal PtrToStructure lParam  typeof LowLevelKeyboardInputEvent                    LowLevelKeyboardInputEvent p    LowLevelKeyboardInputEvent o                   var eventArguments   new GlobalKeyboardHookEventArgs p   KeyboardState wparamTyped                    EventHandler lt GlobalKeyboardHookEventArgs gt  handler   KeyboardPressed                  handler  Invoke this  eventArguments                    fEatKeyStroke   eventArguments Handled                             return fEatKeyStroke    IntPtr 1   CallNextHookEx IntPtr Zero  nCode  wParam  lParam                       Usage   using System  using System Windows Forms   namespace SnagFree TrayApp Core       internal class Controller   IDisposable               private GlobalKeyboardHook  globalKeyboardHook           public void SetupKeyboardHooks                          globalKeyboardHook   new GlobalKeyboardHook                 globalKeyboardHook KeyboardPressed    OnKeyPressed                     private void OnKeyPressed object sender  GlobalKeyboardHookEventArgs e                          Debug WriteLine e KeyboardData VirtualCode                if  e KeyboardData VirtualCode    GlobalKeyboardHook VkSnapshot                  return                  seems  not needed in the life                if  e KeyboardState    GlobalKeyboardHook KeyboardState SysKeyDown  amp  amp                    e KeyboardData Flags    GlobalKeyboardHook LlkhfAltdown                                    MessageBox Show  Alt   Print Screen                      e Handled   true                                else              if  e KeyboardState    GlobalKeyboardHook KeyboardState KeyDown                                MessageBox Show  Print Screen                    e Handled   true                                   public void Dispose                          globalKeyboardHook  Dispose

User · Answer

private void buttonHook Click object sender  EventArgs e           Hooks only into specified Keys  here  quot A quot  and  quot B quot                 Use this constructor       globalKeyboardHook   new GlobalKeyboardHook new Keys     Keys A  Keys B             Hooks into all keys               Or this - not both       globalKeyboardHook   new GlobalKeyboardHook         globalKeyboardHook KeyboardPressed    OnKeyPressed     And then is working fine

User · Answer

My rep is too low to comment  but concerning the CallbackOnCollectedDelegate exception  I modified the public void SetupKeyboardHooks   in C4d s answer to look like this  public void SetupKeyboardHooks out object hookProc       globalKeyboardHook   new GlobalKeyboardHook       globalKeyboardHook KeyboardPressed    OnKeyPressed      hookProc    globalKeyboardHook GcSafeHookProc     where GcSafeHookProc is just a public getter for  hookProc in OPs  hookProc   LowLevelKeyboardProc     we must keep alive  hookProc  because GC is not aware about SetWindowsHookEx behaviour   and stored the hookProc as a private field in the class calling the SetupKeyboardHooks       therefore keeping the reference alive  save from garbage collection  no more CallbackOnCollectedDelegate exception  Seems having this additional reference in the GlobalKeyboardHook class is not sufficient  Maybe make sure that this reference is also disposed when closing your app

[.net] Global keyboard capture in C# application

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