KeyEventArgs and KeyPressEventArgs Examples in VS .NET

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Table 81 KeyEventArgs and KeyPressEventArgs Examples
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Keys Pressed I Shift+I KeyData KeysI KeysShift + KeysI KeyCode KeysI KeysI KeysI Modifiers KeysNone KeysShift KeysCtrl + KeysShift Alt Ctrl Shift KeyValue KeyChar 73 73 73 i I n/a
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false false false false false true false true true
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Ctrl+Shift+I KeysCtrl + KeysShift + KeysI Ctrl
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KeysControlKey KeysControlKey KeysControl false true + KeysCtrl
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false
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The return from IsInputKey indicates whether or not the key data should be sent in events to the control In this example, IsInputKey returns true for all the arrow keys and lets the base class decide what to do about the other keys
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If you'd like to know the state of a modifier key outside a key event, you can access the state in the static ModifierKeys property of the Control class For example, the following checks to see whether the Ctrl key is the only modifier to be pressed during a mouse click event: void EllipseLabel_Click(object sender, EventArgs e) { if( ControlModifierKeys == KeysControl ) { MessageBoxShow("Ctrl+Click detected"); } }
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Windows Message Handling
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The paint event, the mouse and keyboard events, and most of the other events handled by a custom control come from the underlying Windows operating system At the Win32 level, the events start out life as Windows messages A Windows message is most often generated by Windows because of some kind of hardware event, such as the user pressing a key, moving the mouse, or bringing a window from the background to the foreground The window that needs to react to the message gets the message queued in its message queue That's where WinForms steps in The Control base class is roughly equivalent to the concept of a window in the operating system It's the job of WinForms to take each message off the Windows message queue and route it to the Control responsible for handling the message The base Control class turns this message into an event, which Control then fires by calling the appropriate method in the base class For example, the WM_PAINT Windows message eventually turns into a call on the OnPaint method, which in turn fires the Paint event to all interested listeners However, not all Windows messages are turned into events by WinForms For those cases, you can drop down to a lower level and handle the messages as they come into the Control class You do this by overriding the WndProc method:
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protected override void WndProc(ref Message m) { // Process and/or update message // Let base class handle it if you don't baseWndProc(ref m); } As a somewhat esoteric example of handling Windows messages directly, the following is a rewrite of the code from 2: Forms to move the nonrectangular form around the screen: protected override void WndProc(ref Message m) { // Let the base class have first crack baseWndProc(ref m); int WM_NCHITTEST = 0x84; // winuserh if( mMsg != WM_NCHITTEST ) return; // If the user clicked on the client area, // ask the OS to treat it as a click on the caption int HTCLIENT = 1; int HTCAPTION = 2; if( mResultToInt32() == HTCLIENT ) mResult = (IntPtr)HTCAPTION; } This code handles the WM_NCHITTEST message, which is one of the few that WinForms doesn't expose as an event In this case, the code calls to the Windows-provided handler for this message to see whether the user is moving the mouse over the client area of the form If that's the case, the code pretends that the entire client area is the caption so that when the user clicks and drags on it, Windows will take care of moving the form for us There aren't a whole lot of reasons to override the WndProc method and handle the Windows message directly, but it's nice to know that the option is there in case you need it
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