Class

A class is defined by its name, its parent class and a dispatcher.

• name: either a string for the public classes, so that they may be used by any program in the system, or none if its a private class used only by a single application.
• parent class: all BOOPSI classes are forming a hierarchy rooted at the class aptly named rootclass. It allows each subclass to implement its own version of specific parent operation, or to fall back on the one provided by its parent. Also known as base class or super class.
• dispatcher: it gives access to all operations (called methods) provided by this class, ensuring that each operation is handled by the proper code or passed to its super class.

BOOPSI type for a class is Class * also known as IClass.

Object

An object is an instance of class: each object has its specific data, but all objects of the same class share the same behavior. An object has several classes if we count the parents of its true class (the most derived one) up to the rootclass.

BOOPSI type for an object is Object *. It has no field you can directly access.

Attribute

An attribute is related to the instance data of each object: you can't access these data directly, you can only set or get the attributes provided by an object to modify its internal state. An attribute is implemented as a Tag (ULONG value or'ed with TAG_USER).

GetAttr() and SetAttrs() are used to modify an object's attributes.

Attributes can be one or more of the following:

• Initialization-settable (I) : the attribute can be given as parameter at the object creation.
• Settable (S) : You can set this attribute at any time (or at least, not only creation).
• Gettable (G) : You can get the value of this attribute.

Method

A BOOPSI method is a function which receives as parameters an object, a class and a message:

• object: the object you act on
• class: the considered class for this object.
• message: contains a method ID which determines the function to call within a dispatcher, and is followed by its parameters.

To send a message to an object, use DoMethod(). It will use the true class first. If the class implements this method, it will handle it. Else it will try its parent class, until the message is handled or the rootclass is reached (in this case, the unknown message is silently discarded).

Getting an attribute

We'll query a MUI String object for its content:

void f(Object *string)
{
    IPTR result;

    GetAttr(string, MUIA_String_Contents, &result);
    printf("String content is: %s\n", (STRPTR)result);
}

• Object * is the type of BOOPSI objects.
• IPTR must be used for the type of the result, which can be an integer or a pointer. An IPTR is always written in memory, so using a smaller type would lead to memory corruption!
• Here we query a MUI String object for its content: MUIA_String_Contents, as any other attribute, is a ULONG (it's a Tag)

Zune applications use more often the get() and XGET() macros instead:

get(string, MUIA_String_Contents, &result);

result = XGET(string, MUIA_String_Contents);

Setting an attribute

Let's change the content of our string:

SetAttrs(string, MUIA_String_Contents, (IPTR)"hello", TAG_DONE);

• Pointers parameters must be casted to IPTR to avoid warnings.
• After the object parameter, a taglist is passed to SetAttrs and thus must end with TAG_DONE.

You'll find the set() macro useful:

set(string, MUIA_String_Contents, (IPTR)"hello");

But it's only with SetAttrs() that you can set several attributes at once:

SetAttrs(string,
         MUIA_Disabled, TRUE,
         MUIA_String_Contents, (IPTR)"hmmm...",
         TAG_DONE);

Calling a method

Let's see the most called method in a Zune program, the event processing method called in your main loop:

result = DoMethod(obj, MUIM_Application_NewInput, (IPTR)&sigs);

• Parameters are not a taglist, and thus don't end with TAG_DONE.
• You have to cast pointers to IPTR to avoid warnings.

General

We don't manually open libraries, it's done automatically for us.

GUI creation

We use a macro-based language to easily build our GUI. A Zune application has always 1 and only 1 Application object:

:    app = ApplicationObject,

An application can have 0, 1 or more Window objects. Most often a single one:

:        SubWindow, wnd = WindowObject,

Be nice, give a title to the window:

:        MUIA_Window_Title, "Hello world!",

A window must have 1 and only 1 child, usually a group. This one is vertical, that means that its children will be arranged vertically:

:        WindowContents, VGroup,

A group must have at least 1 child, here it's just a text:

:            Child, TextObject,

Zune accepts various escape codes (here, to center the text) and newlines:

:            MUIA_Text_Contents, "\33cHello world!\nHow are you?",

An End macro must match every xxxObject macro (here, TextObject):

:            End,

Let's add a second child to our group, a button! With a keyboard shortcut o indicated by an underscore:

:            Child, but = SimpleButton("_Ok"),

Finish the group:

:            End,

Finish the window:

:        End,

Finish the application:

:        End;

So, who still needs a GUI builder? :-)

Error handling

If any of the object in the application tree can't be created, Zune destroys all the objects already created and application creation fails. If not, you have a fully working application:

:    if (app != NULL)
:    {
:        ...

When you're done, just call MUI_DisposeObject() on your application object to destroy all the objects currently in the application, and free all the resources:

:       ...
:        MUI_DisposeObject(app);
:    }

Notifications

Notifications are the simplest way to react on events. The principle? We want to be notified when a certain attribute of a certain object is set to a certain value:

:        DoMethod(wnd, MUIM_Notify, MUIA_Window_CloseRequest, TRUE,

Here we'll listen to the MUIA_Window_CloseRequest of our Window object and be notified whenever this attribute is set to TRUE. So what happens when a notification is triggered? A message is sent to an object, here we tell our Application to return MUIV_Application_ReturnID_Quit on the next event loop iteration:

:                 (IPTR)app, 2,
:                 MUIM_Application_ReturnID, MUIV_Application_ReturnID_Quit);

As we can specify anything we want here, we have to tell the number of extra parameters we are supplying to MUIM_Notify: here, 2 parameters.

For the button, we listen to its MUIA_Pressed attribute: it's set to FALSE whenever the button is being released (reacting when it's pressed is bad practice, you may want to release the mouse outside of the button to cancel your action - plus we want to see how it looks when it's pressed). The action is the same as the previous, send a message to the application:

:        DoMethod(but, MUIM_Notify, MUIA_Pressed, FALSE,
:                 (IPTR)app, 2,
:                 MUIM_Application_ReturnID, MUIV_Application_ReturnID_Quit);

Opening the window

Windows aren't open until you ask them to:

:        set(wnd, MUIA_Window_Open, TRUE);

If all goes well, your window should be displayed at this point. But it can fail! So don't forget to check by querying the attribute, which should be TRUE:

:        if (XGET(wnd, MUIA_Window_Open))

Main loop

Let me introduce you my lil' friend, the ideal Zune event loop:

:        ULONG sigs = 0;

Don't forget to initialize the signals to 0 ... The test of the loop is the MUIM_Application_NewInput method:

:        ...
:        while((LONG) DoMethod(app, MUIM_Application_NewInput, (IPTR)&sigs)
:              != MUIV_Application_ReturnID_Quit)

It takes as input the signals of the events it has to process (result from Wait(), or 0), will modify this value to place the signals Zune is waiting for (for the next Wait()) and will return a value. This return value mechanism was historically the only way to react on events, but it was ugly and has been deprecated in favor of custom classes and object-oriented design.

The body of the loop is quite empty, we only wait for signals and handle Ctrl-C to break out of the loop:

:        {
:            if (sigs)
:            {
:                sigs = Wait(sigs | SIGBREAKF_CTRL_C);
:                if (sigs & SIGBREAKF_CTRL_C)
:                    break;
:            }
:        }

Conclusion

This program gets you started with Zune, and allows you to toy with GUI design, but not more.

Compiling

To compile this simple program with i386-aros-gcc cross-compiler please use this command:

i386-aros-gcc -o hello -D__AROS__ hello.c -lmui