GNUstep development tools : a basic tutorial
This tutorial will introduce you to creating a GNUstep application
Creating an App
Launch ProjectCenter.app and select Project->New. In the "New
Project..." dialog, select Application.
Select the location of your application , give it a name (here we chose
"Converter") and press OK.
Editing the interface file
Select Interfaces in the main window browser. The project interface
files will appear. Depending on the version of ProjectCenter you might
find several versions of the interface (renaissance markup, for
example). Since we are concentrating on the graphical editor Grom, you
may safely remove the the other interfaces from the project with
Project->Remove Files and using "Project and Disk".
Select Convertor.gorm (or name_of_your_app
.gorm) and click on
it. That should launch Gorm automatically and open the file.
Gorm first contact
Here is what you'll get once you've double-clicked the .gorm file.
If the Palettes and Tools don't display automatically for you, show
them using: Select Tools->Inspector... and Tools->Palettes...
Then you'll see the Palettes and Insepector windows.
The Palettes Window contains many palettes. Each of the palettes
contains components which can be drag-and-dropped to the interface
From the Windows Palette
a "Window" into the Gorm Document. A Window will be instantiated and
Rename the title
of "My Window" to, for example, "Converter".
To do that, check in the Inspector
property. Change it
to the name you need (e.g. Converter) and hit enter. The title of the
instantiated Window will automatically change.
You may also want to change the name of the Window Object. Although
this does not have effect for the user interface, it helps when having
many windows and objects instantiated to identify the correct one.
Select it and choose Edit->SetName. Set it to something like MainWin
: the name is for
identification purposes only.
In the Attributes of the Window also tick the Visible at launch time
will show the window automatically when the application is launched.
Creating the interface
Try to drag-and-drop some Text, Title and Button components to the
Converter window. Drag the items you need from the Palette (Controls Palette
). Move things in
order to obtain an interface that looks close to the following one.
Resize the Controls and the window using the Handles.
You can change the values of the control strings by directly
double-clicking and doing in-line editing. Don't forget to press
"Enter" or to click OK once you've
finished editing the value.
Change the string values of the components to obtain the following.
You can readjust the sizes to match the new labels, guidelines will
appear to help you aligning the elements and you can also use the arrow
keys to do precise movements.
Creating a subclass
Now select the "Classes" part of the main window. Select the NSObject
class and do Classes->Create Subclass..., in order to create a
of NSObject. It will be called "NewClass"
You should then see the following inspector window. If not select the
new class (which should still be called NewClass) in the class browser
the main window, and do Classes->Edit Class...
Rename the class from NewClass to ConvertorManager (don't forget to
press Enter, or your change will not affect anything).
Adding outlets & actions
Now let's add some outlets. Outlets are basically instance variables of
the class that you will connect to interface's components at design
time. Outlets represent the components you want to work with and of
which you need to work in the code. Connecting them means interfacing
the code with the gorm interface. To edit Outlets you need select
ConvertorManager and get back into the Classes
view, the Inspector will
So add three outlets : "amount", "rate", "result". Adding an outlet
creates a new outlet called newOutlet
You will now create an action. An action is an object method which can
be linked to interface's component at design time, so that a specific
action on the component will get this method to be called. Actions
specify interaction from
the interface to the code, they are methods to which the interface will
send messages. Actions carry as a parameter a sender
which is the control
generating the call.
Add one action named "convert:", please notice the ":
" at the
Instantiating the class
Now that we have defined the class's outlets and actions, we need to
it. Do select Classes->Instantiate. Doing this tells GNUstep to
an instance of this class when the application is launched (to be more
when the nib/gorm file is loaded.) You should now see a new object
in the Objects part of Gorm's main panel.
Connecting outlets and actions
We now need to connect the outlets of the instance of ConvertorManager
have created to their corresponding components. As you may have
the amount outlet is to be connected to the first text field, rate to
second and result to the third.
Done that, the ConvertorManager instance will be able to access those
by using its instance variables. You will not have any code to write to
have those connections up and working.
To connect the amount outlet to the first text field, you have to
drag-and-drop while pressing the Control key from the ConvertorManager
instance (the instance
is in the Classes part of Gorm's main panel) to the first text field.
icons will appear showing who is the Source
and who is the
(those icons always appear in the bottom-left corner, if they
you are probably not selecting the component you want to select).
After drag-and-dropping, you have to select which outlet of the Source
you want to connect to the target, do this by clicking the correct
outlet in the
Outlets column of the Inspector and by pressing the connect button. Do
for all three outlets amount, rate, result.
Connecting an action is a similar operation. Do a drag-and-drop
with the control key pressed, from the Convert button to the instance
of ConvertorManager. Then click target in the Outlets part of the
inspector, all available actions of the target (here the
ConvertorManager instance which has only one action) will appear in the
Actions column. Click on the convert: action, and press the connect
button. Now, every time the convert button is pressed it send a convert:
message to the instance of
ConvertorManager. The sender
will be the Button.
Creating the class's source and header files
Gorm.app can automatically create the skeleton of the class you've
designed: select the ConvertorManager class in the Classes panel of
the main window, and do Classes->Create Class's Files.
Two successive Save Panels will pop up for the .m and the .h files.
Gorm will propose as file names ConvertorManager.m and
ConvertorManager.h, it is a good convetion to use the class name as a
those files into the Project directory.
You may also safely delete the "AppController" object instance if you
have it in your Gorm file.
Once this is done, remember to save the interface if you haven't yet,
back to ProjectCenter.app.
Adding the class's source and header files to the current project
You now need to add the class's files to the project. Double-click
"Classes" in the first column of the browser, choose the .m file to add
to the project (ConvertorManager.m); the corresponding header file will
be automatically added for you.
Writing the convert: method
Open the ConvertorManager.m file by slecting its name within
ProjectCenter.app browser. YOu can display the file in the embedded
view or, alternatively, double-clicking will open it in a separate
You should see the following :
/* All Rights reserved */
- (void) convert: (id) sender
/* insert your code here */
Add the following inside the convert: method:
[result setFloatValue: [rate floatValue] * [amount floatValue]];
or if you want to have a nicer dispaying :
[result setStringValue: [NSString stringWithFormat: @"%1.2f",
[amount floatValue] * [rate floatValue]]];
Save the file.
You may safely remove the AppController class from your project, we are
not using it.
Compiling and running
to dispay the building panel.
to build the project. If
there is no
errors (and hopefully there is none), you can run the application. To
do it, click
to display the run panel. Then
click the first button (at this time it has still no icon), this should
launch the application :
Convertor.app in action, converting between Euro and US Dollar.
Congratulations, you have made your first GNUstep application.
Initial writing 07-07-2001
Modified 02-Feb-2005 by Alex Perez
Updated 13-Nov-2010 Riccardo Mottola
Copyright © 2001, 2005 Pierre-Yves Rivaille