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Week Four Homework

Week 4 Homework

Liberty BASIC programming course

Using NOMAINWIN

The default text window that opens with each Liberty BASIC program we create can be optionally turned off. This can be desirable when we don't want our application to be operated out of a text window. The statement that accomplishes this effect is NOMAINWIN. Simply include NOMAINWIN in your program's source code anywhere at all. This accomplishes two things:

1) It hides the program's main window;

2) It prevents the 'Execution Complete' notice from appearing at the end of a program run.

This comes at a cost. Your program must close itself down properly when all the windows have been closed. Below is a modified version of our WK4PROG6.BAS program. In this case all we needed to do was add the NOMAINWIN statement. No other changes are needed because we have an END statement after our example window and because we don't use the program's main window for anything.

'WK4PROG7.BAS - (WK4PROG6.BAS modified)

'open a window with a button, a textbox, and a statictext

'show how trapclose works

'the window is sized at 300 by 100 at position 200, 150

nomainwin 'do not open a main window

WindowWidth = 300

WindowHeight = 100

UpperLeftX = 200

UpperLeftY = 150

button #myFirst.ok, "OK!", [okClicked], UL, 220, 35

textbox #myFirst.field, 10, 35, 200, 25

statictext #myFirst.label, "Type some text here.", 10, 10, 150, 25

open "myname's first window!" for window as #myFirst

'send the trapclose command

print #myFirst, "trapclose [quit]"

'now stop and wait

wait

[okClicked] 'OK! was clicked. Get the contents of the entry field

'now get the contents from the textbox

print #myFirst.field, "!contents? aString$"

'now pop up a notice saying what was in the textbox

notice aString$

[quit]

'ask if the user wants to quit

confirm "Really Quit?"; answer$

if answer$ <> "yes" then wait 'abort quitting

'now close the window

close #myFirst

end

After the CLOSE #myFirst statement in our program above, we have an END statement. If we didn't, then our program would not terminate properly, and there would be no error message to clue us in. Always use END in your programs because just closing all the windows doesn't end the program. There are kinds of programs which don't have windows open all the time, and even some which don't have any windows at all.

The Structure of a Liberty BASIC GUI Program

We've taken a look at some simple elements of Liberty BASIC GUI programming. Now let's consider how to organize code in a logical and practical way when creating GUI programs in LB.

Organization

In the case of a project that uses more than one window, we should make sure that code for each window is grouped together. Most applications are designed around a cental window that is always open and from where other windows are launched. When the central window is closed, the application ends. Here is a simple outline (not a working program) that demonstrates this idea:

'MYPROG.BAS

'This is an example outline

'A description of the program should go here

'-----------------------Let's define our main application window here

button #main.1, ....

button #main.2, ....

textbox ....

open "My Application" for window as #main

print #main, "trapclose [closeMain]"

'wait here for user action

wait

[button1Clicked] 'here is a routine that handles when a button is clicked

'do something here

'now wait

wait

[button2Clicked] 'here is a routine that handles when a button is clicked

'do something here

'now wait

wait

[closeMain] 'perform some cleanup code and close the window

close #main

gosub [sub1] 'act on user action

'end application

end

[openWin2] '--------------------------Let's define our second window here

button #2.3, ....

button #2.4, ....

textbox ....

open "Window 2" for window as #2

print #2, "trapclose [close2]"

'wait here for user action

wait

[button3Clicked] 'here is a routine that handles when a button is clicked

'do something here

'now wait

wait

[button4Clicked] 'here is a routine that handles when a button is clicked

'do something here

'now wait

wait

[close2] 'perform some cleanup code and close the window

close #2

gosub [sub2] 'act on user action

'now wait

wait

'--------------------------------------------------------------------------

'We might place code here containing general subroutines

See how we arrange the code for each window like so:

[openMainWindow]

[userAction1]

[userAction2]

[closeMainWindow]

end

[openWindow1]

[userAction3]

[userAction4]

[closeWindow1]

[openWindow2]

[userAction5]

[userAction6]

[closeWindow2]

The names we give to our branch labels above are of course generic. All the code for a given window and user actions performed on it should be grouped together. By structuring things in this way it is relatively easy to develop and debug your programs.

NOTE: Be careful to avoid creating a program that closes all its windows but doesn't actually end. If the program stops at an input or wait statement after closing all of it's windows, it will not terminate properly and resources will not be freed. If the program loops continuously after closing all its windows then our WINDOWS message handler (the one set up to Liberty BASIC) will be locked out. In this case press CTRL-Break to halt the errant program.

Using Dialog Boxes

Dialog boxes are a special kind of window. They are different in several respects from other windows:

1) Pressing the Tab key causes WINDOWS to cycle through the controls added to a dialog box. Each control is made the active one in turn. In Liberty BASIC 3, a window of type 'window' will also allow cycling through the controls by pressing the Tab key.

2) Dialog boxes can be made modal. This means that if I have a first window open and then I open a modal dialog box, that I will be unable to select the first window until the modal dialog is closed. Most 'About' boxes are modal dialogs, as are many 'Properties' type windows. For an example, select Liberty BASIC's Help menu and click on 'About Liberty BASIC'. You won't be able to do anything else with Liberty BASIC until you close the dialog box that appears.

3) Dialog boxes cannot be resized by the user.

Some applications are appropriately constructed completely of dialog boxes and have no other kind of window at all. Take a look at the program FreeForm which comes with Liberty BASIC. This program is more typical. The main application windows is a graphics type, but most of the other windows are dialog boxes.

'Canned' Dialog Boxes

There are some simple preconstructed dialog boxes in Liberty BASIC. These are useful for displaying simple notices, asking for a yes and no response, prompting the user to type some string, or selecting a filename from a list of filenames.

Here are some examples:

'display a notice

notice "File Not Found!"

'ask a yes or no question

confirm "Would you like to skip the tutorial?"; answer$

'prompt for input string

prompt "Please enter your name:"; name$

'get a filename from the user

filedialog "Pick a text file", "*.txt", selection$

There are right and wrong times to use these kinds of dialogs. Here is the HILO.BAS program written using only the above dialog boxes. This illustrates a wrong way to write a WINDOWS program.

What is wrong with the program above? Technically there is nothing wrong with it because it works. However one obvious thing wrong is that there's only one place where you can exit the program (at the end of each game). It also looks sloppy. It doesn't have one application window that is open all the time as most WINDOWS programs do, so it will seem strange to most users.

More About Statictext

We saw in our earlier installment of this Week 4 lesson how a statictext control is used to label other controls in a window. Statictext controls do not have to display the same label throughout the course of the program. We can print to them in similar fashion to the way we print to a textbox control. Try the example code below:

'WK4PROG9.BAS

'demonstrate printing to statictext control

statictext #countdown.stext, "Counting down:", 10, 10, 200, 25

open "Countdown" for window as #countdown

for count = 10 to 1 step -1

print #countdown.stext, "Counting down: "; count

t$ = time$()

while t$ = time$()

wend

next count

print #countdown.stext, "Counting Down: Done."

end

Homework Assignment

Create a version of the WK4PROG8.BAS program above (call it MYHILO.BAS). The program should have its own application window using the dialog window type. This window should have at least one statictext control. One of these should indicate whether to guess higher or lower and to count the guesses. There should be a textbox for entering guesses, and a button labeled guess to click on to register each guess. An additional button should be labeled 'About'. This button should cause an About box to be displayed for the game. The About box can be a canned dialog box, or you can construct one yourself using a modal dialog box.

Week Four Homework Solution