JanetTerra
Jul 2, 2007
==Coding with Sub Event Handlers== ===Janet Terra=== [[toc]] Liberty BASIC supports both **//Branch Label//** handling and **//Sub//** handling for control events. Alyce Watson [[http://babek.info/libertybasicfiles/lbnews/nl137/Home.htm|Liberty BASIC Newsletter Issue #137]], [[http://babek.info/libertybasicfiles/lbnews/nl137/tip.htm|Tip Corner - a SUB for Resizehandler]] discussed local visibility and global visibility in terms of coding a resizehandler. A sub can call another sub, but a sub cannot branch to a branch label outside that sub. Using all subs may prevent a program crash due to //unseen// branch labels. Another distinct advantage of using a sub handler rather than a branch label handler for control events is that the handle of the selected control is passed into the sub. The defined sub must contain a string variable to receive the handle, but any handle can be passed. This allows for multiple controls accessing the same sub. Of course multiple controls may be directed to the same branch label, but the branch label has no way of discerning which control triggered the code. In a sub, the passed handle can be parsed for identification. If you are using a number of like controls, this parsing may afford more streamlined code. [[#OneSubManyLabel]] ===One Sub Rather than Many Branch Labels=== Consider a program with 5 buttons. Each button is designed to launch a different application. Using branch labels, a separate branch label is required for each button. [[code format="vbnet"]] Nomainwin WindowWidth = 200 WindowHeight = 300 UpperLeftX = Int((DisplayWidth - WindowWidth)/2) UpperLeftY = Int((DisplayHeight - WindowHeight)/2) Menu #main, "&Options", "E&xit", [EndDemo] Button #main.app1, "Notepad", [app1], UL, 30, 20, 110, 20 Button #main.app2, "MS Paint", [app2], UL, 30, 50, 110, 20 Button #main.app3, "Calculator", [app3], UL, 30, 80, 110, 20 Button #main.app4, "Sound Recorder", [app4], UL, 30, 110, 120, 20 Button #main.app5, "Spider", [app5], UL, 30, 140, 120, 20 Open "Launching Applications" for Window as #main #main, "Trapclose [EndDemo]" Wait [EndDemo] Close #main End [app1] Run "Notepad.exe" Wait [app2] Run "MSPaint.exe" Wait [app3] Run "Calc.exe" Wait [app4] Run "sndrec32.exe" Wait [app5] Run "Spider.exe" Wait [[code]] With a sub event handler, that code can be greatly optimized. [[code format="vbnet"]] 'Choose 5 common MS Applications App$(1) = "Notepad.exe" App$(2) = "MSPaint.exe" App$(3) = "Calc.exe" App$(4) = "sndrec32.exe" App$(5) = "Spider.exe" Nomainwin WindowWidth = 200 WindowHeight = 300 UpperLeftX = Int((DisplayWidth - WindowWidth)/2) UpperLeftY = Int((DisplayHeight - WindowHeight)/2) Menu #main, "&Options", "E&xit", [EndDemo] Button #main.app1, "Notepad", App2Run, UL, 30, 20, 110, 20 Button #main.app2, "MS Paint", App2Run, UL, 30, 50, 110, 20 Button #main.app3, "Calculator", App2Run, UL, 30, 80, 110, 20 Button #main.app4, "Sound Recorder", App2Run, UL, 30, 110, 120, 20 Button #main.app5, "Spider", App2Run, UL, 30, 140, 120, 20 Open "Launching Applications" for Window as #main #main, "Trapclose [EndDemo]" Wait [EndDemo] Close #main End Sub App2Run handle$ app = Val(Right$(handle$, 1)) Run App$(app) End Sub [[code]] The common sub is then parsed for the control that triggered it and the appropriate code is executed. Constructing an array that correlates with the numbered handle extensions, as in the preceding demo, will streamline your code even further. [[#MenusContMouse]] ===Menus, Controls, and Mouse Events=== When using a branch label, menu items, controls (buttons, listboxes, comboboxes, etc.), and even mouse events, can branch to the same label. [[code format="vbnet"]] Nomainwin WindowWidth = 250 WindowHeight = 154 Menu #main, "&File", "&Random Color", [RandomColor],|, "E&xit", [EndDemo] Graphicbox #main.gbx, 0, 0, 100, 100 Button #main.btn, "Random Color", [RandomColor], UL, 120, 10, 100, 30 Button #main.exit, "Quit", [EndDemo], UL, 120, 50, 100, 30 Open "Sharing Branch Labels" for Window as #main #main, "Trapclose [EndDemo]" #main.gbx, "Down" #main.gbx, "When leftButtonUp [RandomColor]" Wait [EndDemo] Close #main End [RandomColor] redHue = Int(Rnd(1) * 256) greenHue = Int(Rnd(1) * 256) blueHue = Int(Rnd(1) * 256) #main.gbx, "Fill ";redHue;" ";greenHue;" ";blueHue Wait [[code]] Because handles are passed to subs, different event handles may need to be assigned for different types of control. Menus do not pass handles, controls do. A mouse movement passes not only the handle, but also the current {{MouseX}} and {{MouseY}} coordinates. Event handling subs must be assigned that will accommodate these handles and parameters. The menu sub with no handle variable must be different from the button sub requiring a handle variable which must be different from the mouse event sub requiring a handle variable and {{MouseX}} / {{MouseY}} parameters. This doesn't mean that code needs to be duplicated in each sub. Simply call one sub from another. In this demo, the menu and the left mouse click both call the button code, as though the button itself had been clicked. Exiting with the menu option calls the trapclose exit sub. [[code format="vbnet"]] Nomainwin WindowWidth = 250 WindowHeight = 154 Menu #main, "&File", "&Random Color", RandomColorMenu,|, "E&xit", XbyMenu Graphicbox #main.gbx, 0, 0, 100, 100 Button #main.btn, "Random Color", RandomColor, UL, 120, 10, 100, 30 Button #main.exit, "Quit", EndDemo, UL, 120, 50, 100, 30 Open "Assigning Subs" for Window as #main #main, "Trapclose XbyTrap" #main.gbx, "Down" #main.gbx, "When leftButtonUp RandomColorMouse" Wait Sub XbyMenu Call XbyTrap "#main" End Sub Sub XbyTrap handle$ Close #main End End Sub Sub RandomColorMenu Call RandomColor "#main.btn" End Sub Sub RandomColorMouse handle$, xVar, yVar Call RandomColor "#main.btn" End Sub Sub RandomColor handle$ redHue = Int(Rnd(1) * 256) greenHue = Int(Rnd(1) * 256) blueHue = Int(Rnd(1) * 256) #main.gbx, "Fill ";redHue;" ";greenHue;" ";blueHue End Sub [[code]] Remember you will need to include the missing parameters whenever a sub event is being called from another sub. The menu exit option must include a handle to be passed when calling the trapclose sub event. Unless you are parsing, this parameter doesn't have to be valid. [[code format="vbnet"]] Call EndDemo "whatchamacallit" [[code]] or even [[code format="vbnet"]] Call EndDemo "" [[code]] will work just as well as [[code format="vbnet"]] Call EndDemo "#main" [[code]] provided the handle$ variable isn't being relied upon in the sub. In the [[http://babek.info/libertybasicfiles/lbnews/nl126/index.htm|Liberty BASIC Newsletter Issue #126]], Mike Bradbury uses one sub event handler to identify and manage seating arrangements using 48 separate graphicboxes [[http://babek.info/libertybasicfiles/lbnews/nl126/subhandlers.htm|Demo: Sub Handlers]]. That same program would require 48 separate branch label events. Aside from streamlining code, there is at least one more advantage to using event sub handlers -- keeping track of open windows. [[#ManageMultWin]] ===Managing Multiple Windows with Sub Events=== When multiple windows can be opened by the user within the same application, the programmer must find a way to know which windows are opened and which are closed. Using sub events can help the program to keep track of open windows and prevent program crashes from trying to reopen an already open window, or from trying to end with one or more windows still open. In this next demo, an array is used to keep track of open windows. When the window is opened, the handle is passed into the array. When the window is closed, the array element is reset to null. Looping through the array when closing the main window finds which handles have yet to be closed. [[code format="vbnet"]] Dim OpenWindow$(12) Nomainwin WindowWidth = 400 WindowHeight = 400 UpperLeftX = Int((DisplayWidth - WindowWidth)/2) UpperLeftY = Int((DisplayHeight - WindowHeight)/2) Button #main.w01, "Accessory Window #1", AccWin, UL, 30, 50, 140, 26 Button #main.w02, "Accessory Window #2", AccWin, UL, 30, 100, 140, 26 Button #main.w03, "Accessory Window #3", AccWin, UL, 30, 150, 140, 26 Button #main.w04, "Accessory Window #4", AccWin, UL, 30, 200, 140, 26 Button #main.w05, "Accessory Window #5", AccWin, UL, 30, 250, 140, 26 Button #main.w06, "Accessory Window #6", AccWin, UL, 30, 300, 140, 26 Button #main.w07, "Accessory Window #7", AccWin, UL, 220, 50, 140, 26 Button #main.w08, "Accessory Window #8", AccWin, UL, 220, 100, 140, 26 Button #main.w09, "Accessory Window #9", AccWin, UL, 220, 150, 140, 26 Button #main.w10, "Accessory Window #10", AccWin, UL, 220, 200, 140, 26 Button #main.w11, "Accessory Window #11", AccWin, UL, 220, 250, 140, 26 Button #main.w12, "Accessory Window #12", AccWin, UL, 220, 300, 140, 26 Open "Multiple Windows" for Window as #main #main, "Trapclose XbyTrap" #main, "Font Ariel 8 Bold" Wait Sub EndDemo handle$ For i = 1 to 12 If OpenWindow$(i) <> "" Then winHandle$ = OpenWindow$(i) Close #winHandle$ End If Next i Close #main End End Sub Sub AccWin handle$ win = Val(Right$(handle$, 2)) winHandle$ = "#acc";Right$("0";win, 2) If OpenWindow$(win) <> "" Then Exit Sub ' Don't reopen an already open window End If If win < 7 Then ulx = Int(DisplayWidth / 5) + 1 uly = Int(DisplayHeight / 8) * (win - 1) + 1 Else ulx = Int(DisplayWidth / 5) * 3 + 1 uly = Int(DisplayHeight / 8) * (win - 7) + 1 End If WindowWidth = 100 WindowHeight = 80 UpperLeftX = ulx UpperLeftY = uly title$ = "Accessory Window #";win ' Following requires Case Select because variables cannot be used for handles ' prior to opening the window Select Case win Case 1 Open title$ for Window as #acc01 Case 2 Open title$ for Window as #acc02 Case 3 Open title$ for Window as #acc03 Case 4 Open title$ for Window as #acc04 Case 5 Open title$ for Window as #acc05 Case 6 Open title$ for Window as #acc06 Case 7 Open title$ for Window as #acc07 Case 8 Open title$ for Window as #acc08 Case 9 Open title$ for Window as #acc09 Case 10 Open title$ for Window as #acc10 Case 11 Open title$ for Window as #acc11 Case 12 Open title$ for Window as #acc12 End Select OpenWindow$(win) = winHandle$ ' Now that the window is open, variables can be used for handles #winHandle$, "Trapclose CloseAcc" End Sub Sub CloseAcc handle$ win = Val(Right$(handle$, 2)) Close #handle$ OpenWindow$(win) = "" End Sub [[code]] It is not necessary to number the accessory windows as such. Any names will do. This demo looks at {{OpenWindow$(win)}}. If your window names aren't in any logical sequence, just loop through the entire array to find a match. [[#EndWaitGoto]] ===An End to Multiple WAITS, GOTOs=== Once a sub has been executed, program execution reverts to the state prior to calling the sub. In most cases, your program will need only one WAIT statement. Since the events are triggered by controls, there is no need for a single GOTO statement. In a recent discussion of Sub Events at the [[http://libertybasic.conforums.com|Liberty BASIC Forum]], Carl Gundel, author of Liberty BASIC clarified, "//WAIT does not use GOTO if your event handlers are all SUBs. The SUB will get executed, and when it is finished you will be left at the same WAIT statement.//" So get control of your controls using **Sub Event Handlers**. You may find the results well worth the effort. ----