tips.en

Gambas is a graphical development environment based on a Basic interpreter, like Visual Basic. It us

[WELCOME]

<p>Welcome to <b>Gambas</b> !<img src="img/gambas.png" align=right></p>

<p><b>Gambas</b> is a graphical development
environment based on an advanced <i>Basic</i> interpreter.</p>

<p><b>Gambas</b> aims at enabling you to make
powerful programs easily and quickly. But clean programs
remain on your <i>own</i> responsibility...</p>

<p>Enjoy it !</p>

<p align=right>Beno&icirc;t Minisini<br>
<u>[e-mail]</u></p>


[STARTUP]

<p>Each project must have a <i>startup class</i>. This
startup class must define a static public method named <i>Main</i>
with no arguments, that will act as the startup method of
your program.</p>

<p>You can define the startup class by clicking on it with the
right mouse button in the project tree, and by selecting 
<i>Startup class</i> in the popup menu.</p>

<p>It is not necessary to define a <i>Main</i> method in a startup
form, because it already has a predefined one.</p>

<p>This predefined startup method instanciates the form and shows it, like in
<i>Visual Basic&trade;</i>.</p>


[OPEN]

<p>The <b>OPEN</b> instruction of <b>Gambas</b> does not
work like the <i>Visual Basic</i> one. It does not return the file
as an integer, but as a <i>File</i> object.</p>

<p>So, instead of typing :</p>

<pre>DIM handle AS Integer
...
OPEN "myfile" FOR READ AS #handle</pre>

<p>you must type :</p>

<pre>DIM handle AS File
...
OPEN "myfile" FOR READ AS #handle</pre>


[CATDIR]

<p>Do you know that you can catenate directory names and
file names with the <b><tt>&/</tt></b> operator ? This operator
deals with the trailing slashes so that the resulting path is
perfect.</p>

<p>For example:</p>

<pre>PRINT "/home/gambas" &/ ".bashrc"
/home/gambas/.bashrc

PRINT "/home/gambas/" &/ "/tmp" &/ "foo.bar"
/home/gambas/tmp/foo.bar
</pre>

<p>Isn't it marvellous ?</p>


[EXEC]

<p>You can make an executable file from your entire project. Select
<i>Make executable</i> in the <i>Project</i> menu.</p>

<p>When <b>Gambas</b> makes an executable file, it puts 
the result in the directory of your project by default. 
The executable name has the same name as your project.</p>


[PATH]
<p>
Relative paths have a special meaning in <b><i>Gambas</i></b>.
They always refer to files inside your projects.
<p>
There is no concept of <i>current directory</i>, and no keyword like
<tt>CHDIR</tt> to change it.
<p>
<b>Be careful:</b> you must use relative paths only for accessing
project files, because absolute paths won't work anymore when
you make an executable.


[GLOBAL]

There is <u>no global variables</u> in <b><i>Gambas</i></b>!
<p>
As a workaround, put them in your main module and declare them
as <tt>PUBLIC</tt>.
<p>
If you do not have a main module in your project, but a main
form, then declare them as <tt>STATIC PUBLIC</tt>.
<p>
To access these variables, you must use the name of the main module
or form: <tt>MyMainModule.MyGlobalVariable</tt> or
<tt>MyMainForm.MyGlobalVariable</tt>.


[EMPTY]

<p>To know if a string is empty, it is not necessary to use the
<b>Len()</b> function. You can directly test it, as an empty string
is <b>FALSE</b> and a non-empty string is <b>TRUE</b>.</p>

<p>For example, instead of doing :</p>

<pre>IF Len(MyString) > 0 THEN ...
IF Len(MyString) = 0 THEN ...</pre>

<p>You should do :</p>

<pre>IF MyString THEN ...
IF NOT MyString THEN ...</pre>


[EVENT]

<p>Every control, and every object that can raise events, has an
<i>event observer</i> and an event <i>group name</i>.</p>

<p>The event observer catches every event raised by the object, and
the event group name is the prefix of the procedure called to manage
the event.</p>

<p>By default, this event observer is the object where you have
created the control, and the group name is the name of the control.</p>

<p>This way, a form receives all events raised by the controls you
created inside.</p>

<pre>' Gambas form
DIM hButton AS Button

PUBLIC SUB _new()
&nbsp;&nbsp;hButton = NEW Button(ME) AS "MyButton"
END

PUBLIC SUB MyButton_Click()
&nbsp;&nbsp;PRINT "You have clicked MyButton !"
END
</pre>


[FORM]

<p>In <b><i>Gambas</i></b>, a form is its own event observer, so that 
you can directly manage its events (like <i>Resize</i>, 
<i>Activate</i>, ...) into its own class code.</p>

<p>This way, newbies coming from <i>Visual Basic</i> are not
disorientated :-).</p>


[EMBED]

<p>You can embed any form into other forms with <b><i>Gambas</i></b>
&nbsp;!</p>

<p>To do such a powerful thing, just instanciate the form by passing
a parent container as last argument of the contructor.</p>

<p>For example&nbsp;:</p>
<p><tt>DIM hForm AS MyDialog<br>
DIM hSuperControl AS MyForm<br><br>
' Create a dialog<br>
hForm = NEW MyDialog<br>
' Insert a form into this dialog<br>
' Note that this form takes two parameters before the container<br>
hSuperControl = NEW MyForm(Param1, Param2, MyDialog)<br>
' Moves and resizes the form<br>
hSuperControl.Move(8, 8, 128, 64)<br>
</tt></p>

<p>Be careful: a form embedded into another form is still a form, and
so is its own event observer.</p>


[GROUP]

<p>Every control has a <i>(Group)</i> property. When this property
is set, the prefix of the event handler name is the name of the group
and not the name of the control.</p>

<p>Let's suppose you have a <i>Button</i> named <b>btnAction</b>
with the following <i>Click</i> event handler :</p>

<pre>PUBLIC SUB btnAction_Click()</pre>

<p>If you set the <i>(Group)</i> property of <b>btnAction</b> to
<i>MyGroup</i>, then the event handler that will receive events from
the button will be the following :</p>

<pre>PUBLIC SUB MyGroup_Click()</pre>

<p>This property lets you handle events of different controls in
a single function. And the controls of the same group do not need
to have the same type !</p>

<p><b>Note :</b> The old <i>Visual Basic</i> veteran may recognize
the concept of <i>control array</i>, but in a more powerful
implementation. :-)</p>


[TAG]

<p>Each control has a <i>Tag</i> property. This property is for the
programmer, and can contain any <b>VARIANT</b> data that you find
relevant.</p>

<p>This is very useful, when you want to distinguish controls of the
same group in a common event handler.</p>



[LAST]

<p>The <b>LAST</b> keyword returns the last control that has
received an event. This is very useful when you want to write an
event handler that is independent of any control name.</p>

<p>For example, let's suppose you want to write a calculator program.
You have defined ten buttons, one for each digit, each one in the
same <i>group</i> "Digit". The <i>Tag</i> of each control is set to
the digit drawn in the button. Your event handler may look like that :</p>

<p><tt>PUBLIC SUB Digit_Click()<br><br>
&nbsp;&nbsp;Display = Display & LAST.Tag<br>
&nbsp;&nbsp;RefreshDisplay<br><br>
END</tt></p>


[LEFT]

<p>The well known <i>BASIC</i> routines <b>Left$</b>, <b>Right$</b>
and <b>Mid$</b> have useful behaviours in <b><i>Gambas</i></b></p>

<p>The second parameter of <b>Left$</b> and <b>Right$</b> is
optional, and is one by default.</p>

<p><tt>Left$("Gambas")</tt> returns <tt>"G"</tt><br>
<tt>Right$("Gambas")</tt> returns <tt>"s"</tt></p>

<p>This second parameter can be negative, and then gives the number
of characters not to extract.</p>

<p><tt>Left$("Gambas", -2)</tt> returns <tt>"Gamb"</tt><br>
<tt>Right$("Gambas", -2)</tt> returns <tt>"mbas"</tt></p>

<p>Likewise, the third argument of <b>Mid$</b> can be negative, and
then gives the number of characters from the end of the string
not to extract.</p>

<p><tt>Mid$("Gambas", 2, -2)</tt> returns <tt>"amb"</tt>


[END]

<p>You have read all the tips of the days. I hope you have became
a <b>Gambas</b> expert now ! :-)</p>

<p>If you want to contribute, send new tips to the following
address&nbsp;:</p>
<p><u>[e-mail]</u></p>

<p>Thanks beforehand !</p>