How to detect the currently pressed key

Question

In Windows Forms  you can know  at any time  the current position of the cursor thanks to the Cursors class   The same thing doesn t seem to be available for the keyboard  Is it possible to know if  for example  the Shift key is pressed   Is it absolutely necessary to track down every keyboard notification  KeyDown and KeyUp events

User · Answer

if  Control ModifierKeys    Keys Shift        Shift is pressed   The cursor x y position is a property  and a keypress  like a mouse click mousemove  is an event  Best practice is usually to let the interface be event driven  About the only time you would need the above is if you re trying to do a shift   mouseclick thing

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If you need to listen to keys in any generic class what are pressed when a  Form  Window  this is your code  It doesnt listen to global windows key events  so it cannot be used to see keys when the window is not active  Form cs public partial class Form1   Form       public Form1                    Some other Code            Register all Keys pressed         this KeyPreview   true          KeyHandler Instance Init            this KeyDown    Form1 KeyDown          this KeyUp    Form1 KeyUp             Some other Code in the constructor            private void Form1 KeyUp object sender  KeyEventArgs e                   Fire event when a key is released         KeyHandler Instance FireKeyUp sender  e              private void Form1 KeyDown object sender  KeyEventArgs e                   Fire event when a key is pressed         KeyHandler Instance FireKeyDown sender  e            KeyHandler cs KeyHandler is a Singleton Class and can be accessed in any other Object through Handler Instance     Easy right  public class KeyHandler        region Singleton     private static KeyHandler instance      private KeyHandler                 currentlyPressedKeys   new List lt Keys gt                public static KeyHandler Instance               get                       if  instance is null                                instance   new KeyHandler                              return instance                       endregion Singleton      private List lt Keys gt  currentlyPressedKeys      public List lt Keys gt  GetCurrentlyPressedKeys   get   return currentlyPressedKeys           public void FireKeyDown object sender  KeyEventArgs e                if   currentlyPressedKeys Contains e KeyCode                         currentlyPressedKeys Add e KeyCode               KeyEventKeyPressed sender  e                        public void FireKeyUp object sender  KeyEventArgs e                currentlyPressedKeys Remove e KeyCode           KeyEventKeyReleased sender  e              public event EventHandler lt KeyEventArgs gt  KeyPressed      protected virtual void KeyEventKeyPressed object sender  KeyEventArgs e                EventHandler lt KeyEventArgs gt  handler   KeyPressed          handler  Invoke sender  e              public event EventHandler lt KeyEventArgs gt  KeyReleased      protected virtual void KeyEventKeyReleased object sender  KeyEventArgs e                EventHandler lt KeyEventArgs gt  handler   KeyReleased          handler  Invoke sender  e              public void Init                    Nothing to initialize yet             In any other Class Object its now possible to receive KeyEvents that are fired when the  Form  is active  So its possible to listen to key events in any Control object or anything else  Its possible to see if e g  multiple keys are pressed like Shift Ctrl Q or something like that  public class SomeClass       public SomeClass                 KeyHandler instance KeyPressed    Instance KeyPressed         KeyHandler Instance KeyReleased    Instance KeyReleased             public void SomeMethod                 if  KeyHandler Instance GetCurrentlyPressedKeys Contains Keys ShiftKey                            Do Stuff when the method has a key  e g  Shift Control     pressed                      private void Instance KeyPressed object sender  KeyEventArgs e                   Any Key was pressed  do Stuff then            private void Instance KeyReleased object sender  KeyEventArgs e                   Do Stuff when a Key was Released

User · Answer

In WinForms   if  Form ModifierKeys    Keys Shift     It sounds like a duplicate of Stack Overflow question Detect Shift key is pressed without using events in Windows Forms

User · Answer

You can P Invoke down to the Win32 GetAsyncKeyState to test any key on the keyboard   You can pass in values from the Keys enum  e g  Keys Shift  to this function  so it only requires a couple of lines of code to add it

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Since  NET Framework version 3 0  it is possible to use the Keyboard IsKeyDown method from the new System Windows Input namespace   For instance   if    Keyboard IsKeyDown Key LeftCtrl     Keyboard IsKeyDown Key RightCtrl    amp  amp  Keyboard IsKeyDown Key F            CTRL   F is currently pressed     Even though it s part of WPF  that method works fine for WinForm applications  provided that you add references to PresentationCore dll and WindowsBase dll    Unfortunately  however  the 3 0 and 3 5 versions of the Keyboard IsKeyDown method did not work for WinForm applications   Therefore  if you do want to use it in a WinForm application  you ll need to be targeting  NET Framework 4 0 or later in order for it to work

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You can also look at the following if you use WPF or reference System Windows Input if  Keyboard Modifiers    ModifierKeys Shift   The Keyboard namespace can also be used to check the pressed state of other keys with Keyboard IsKeyDown Key   or if you are subscribing to a KeyDownEvent or similar event  the event arguments carry a list of currently pressed keys

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if   Control ModifierKeys  amp  Keys Shift     0     This will also be true if Ctrl Shift is down   If you want to check whether Shift alone is pressed   if  Control ModifierKeys    Keys Shift    If you re in a class that inherits Control  such as a form   you can remove the Control

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The code below is how to detect almost all currently pressed keys  not just the Shift key   private KeyMessageFilter m filter   new KeyMessageFilter     private void Form1 Load object sender  EventArgs e        Application AddMessageFilter m filter       public class KeyMessageFilter   IMessageFilter       private const int WM KEYDOWN   0x0100      private const int WM KEYUP   0x0101      private bool m keyPressed   false       private Dictionary lt Keys  bool gt  m keyTable   new Dictionary lt Keys  bool gt          public Dictionary lt Keys  bool gt  KeyTable               get   return m keyTable            private set   m keyTable   value               public bool IsKeyPressed                 return m keyPressed             public bool IsKeyPressed Keys k                bool pressed   false           if  KeyTable TryGetValue k  out pressed                         return pressed                     return false             public bool PreFilterMessage ref Message m                if  m Msg    WM KEYDOWN                        KeyTable  Keys m WParam    true               m keyPressed   true                     if  m Msg    WM KEYUP                        KeyTable  Keys m WParam    false               m keyPressed   false                     return false

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Most of these answers are either far too complicated or don t seem to work for me  e g   System Windows Input doesn t seem to exist   Then I found some sample code which works fine  http   www switchonthecode com tutorials winforms-accessing-mouse-and-keyboard-state  In case the page disappears in the future I am posting the relevant source code below   using System  using System Windows Forms  using System Runtime InteropServices   namespace MouseKeyboardStateTest     public abstract class Keyboard          Flags      private enum KeyStates             None   0        Down   1        Toggled   2             DllImport  user32 dll   CharSet   CharSet Auto  ExactSpelling   true       private static extern short GetKeyState int keyCode        private static KeyStates GetKeyState Keys key              KeyStates state   KeyStates None         short retVal   GetKeyState  int key            If the high-order bit is 1  the key is down         otherwise  it is up        if   retVal  amp  0x8000     0x8000          state    KeyStates Down           If the low-order bit is 1  the key is toggled        if   retVal  amp  1     1          state    KeyStates Toggled         return state             public static bool IsKeyDown Keys key               return KeyStates Down     GetKeyState key   amp  KeyStates Down              public static bool IsKeyToggled Keys key               return KeyStates Toggled     GetKeyState key   amp  KeyStates Toggled

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if  Form ModifierKeys    Keys Shift    does work for a text box if the above code is in the form s keydown event and no other control captures the keydown event for the key down   Also one may wish stop further key processing with   e Handled   true

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The best way I have found to manage keyboard input on a Windows Forms form is to process it after the keystroke and before the focused control receives the event  Microsoft maintains a built-in Form-level property named  KeyPreview to facilitate this precise thing   public frmForm                    frmForm KeyPreview   true                 Then the form s  KeyDown   KeyPress  and   or  KeyUp events can be marshaled to access input events before the focused form control ever sees them  and you can apply handler logic to capture the event there or allow it to pass through to the focused form control   Although not as structurally graceful as XAML s event-routing architecture  it makes management of form-level functions in Winforms far simpler  See the MSDN notes on KeyPreview for caveats

User · Answer

if   ModifierKeys    Keys Control   amp  amp    e KeyChar  amp   char Keys F     0             CTRL F pressed

[c#] How to detect the currently pressed key?

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