Today I was asked how the outcome of a button click on a custom dialog could be altered if the ALT or CTRL key was pressed down at the time of the click.<\/p>\n
This is possible by trapping the dialog’s OnKeyDown and OnKeyUp handlers. Using these we can detect if ALT or CTRL is pressed\/released and set a flag accordingly. Then in the button’s OnClick handler we can check the value of this flag and decide what we should do.<\/p>\n
Here’s some example code. Run it and click the button without holding down any keys. You’ll see a message saying that ALT was not pressed. Now click the button while holding down the ALT key and you’ll see the “you clicked the button while ALT was pressed” message. <\/p>\n
Dialog>Dialog1\r\nobject Dialog1: TForm\r\n Left = 467\r\n Top = 241\r\n HelpContext = 5000\r\n BorderIcons = [biSystemMenu]\r\n Caption = 'CustomDialog'\r\n ClientHeight = 212\r\n ClientWidth = 431\r\n Color = clBtnFace\r\n Font.Charset = DEFAULT_CHARSET\r\n Font.Color = clWindowText\r\n Font.Height = -11\r\n Font.Name = 'MS Sans Serif'\r\n Font.Style = []\r\n KeyPreview = True\r\n OldCreateOrder = True\r\n ShowHint = True\r\n OnTaskBar = False\r\n PixelsPerInch = 96\r\n TextHeight = 13\r\n object MSButton1: tMSButton\r\n Left = 147\r\n Top = 47\r\n Width = 75\r\n Height = 25\r\n Caption = 'MSButton1'\r\n TabOrder = 0\r\n DoBrowse = False\r\n BrowseStyle = fbOpen\r\n end\r\nend\r\nEndDialog>Dialog1\r\n\r\nAddDialogHandler>Dialog1,MSButton1,OnClick,doClick\r\nAddDialogHandler>Dialog1,,OnKeyDown,doKeyDown\r\nAddDialogHandler>Dialog1,,OnKeyUp,doKeyUp\r\n\r\nLet>CTRL_DOWN=FALSE\r\nLet>ALT_DOWN=FALSE\r\n\r\nShow>Dialog1,r\r\n\r\nSRT>doClick\r\n \/\/button was clicked, which key is down\r\n If>ALT_DOWN=TRUE\r\n MessageModal>You clicked the button while ALT was pressed\r\n Else\r\n MessageModal>You clicked the button without pressing ALT\r\n Endif\r\nEND>doClick\r\n\r\nSRT>doKeyDown\r\n \/\/is CTRL key pressed\r\n If>DoKeyDown_Key=17\r\n Let>CTRL_DOWN=TRUE\r\n Endif\r\n \/\/is ALT key pressed\r\n If>DoKeyDown_Key=18\r\n Let>ALT_DOWN=TRUE\r\n Endif\r\nEND>doKeyDown\r\n\r\nSRT>doKeyUp\r\n \/\/was ctrl released\r\n If>doKeyUp_Key=17\r\n Let>CTRL_DOWN=FALSE\r\n Endif\r\n \/\/was ALT released\r\n If>doKeyUp_Key=18\r\n Let>ALT_DOWN=FALSE\r\n Endif\r\nEND>doKeyUp<\/pre>\nYou might be wondering how I know that the CTRL key is number 17 and the ALT key is 18. To find out the value of a key press the simplest way is just to pop a breakpoint at the start of the doKeyDown subroutine, then run the script in the debugger, press a key and look in the watch list to see what value is produced. Alternatively there’s a table here<\/a>. Note that ALT is known as VK_MENU and CTRL is VK_CONTROL.<\/p>\n","protected":false},"excerpt":{"rendered":"
Today I was asked how the outcome of a button click on a custom dialog could be altered if the ALT or CTRL key was pressed down at the time of the click. This is possible by trapping the dialog’s OnKeyDown and OnKeyUp handlers. Using these we can detect if ALT or CTRL is pressed\/released […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[6],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/posts\/1864"}],"collection":[{"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/comments?post=1864"}],"version-history":[{"count":7,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/posts\/1864\/revisions"}],"predecessor-version":[{"id":1871,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/posts\/1864\/revisions\/1871"}],"wp:attachment":[{"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/media?parent=1864"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/categories?post=1864"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.mjtnet.com\/blog\/wp-json\/wp\/v2\/tags?post=1864"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}