Newbie question about ENUM and GUI development

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nubechecorre

Posted on: 2016/8/6 23:28 #1

Just can't stay away

Hi Guys,

sorry for this newbie question I apologize but I am going crazy to find an answer (documentation) about the use of C word ENUM inside the development of an Amiga GUI..

I know what is an ENUM in C but what I cannot understand, reading/studying the examples is the use of the ENUM inside the GUI building process..

I have looked through all the wikipage and the ADCD but I wasn't able to find any answer that could give me a clue about it..

What I cannot understand is always this, I took a little part of code that you can find in any example available for the Amiga OS 4.x:

Quote:

enum
{
    WID_MAIN = 0,
    WID_LAST
};

enum
{
    OID_MAIN = 0,
    OID_LAST
};

As you can see there is always an OID_LAST or a WID_LAST but these two elements are not defined inside the GUI layout creation.. They are always put inside the code as last elements of a list of objects that toghether define the gui of your project but what I would like to know is why.. where can i find a proper documentation??

Sorry for this stupid question but while I was able to find documentation about amigaos libraries and exec, I wasn't about this..

May you help me please?


;/* Window Example

gcc -o Window Window.c -lauto

quit

*/



/**

 **  Window.c -- Window Example.

 **

 **  Simple window.class example used to test newer features.

 **/



#include <dos/dos.h>

#include <classes/window.h>

#include <gadgets/button.h>

#include <gadgets/layout.h>



#include <proto/intuition.h>

#include <proto/exec.h>

#include <proto/window.h>

#include <proto/layout.h>

#include <proto/button.h>



enum

{

    WID_MAIN = 0,

    WID_LAST

};



enum

{

    OID_MAIN = 0,

    OID_LAST

};



int main()

{

    // Make sure class files were loaded.

    if ( WindowBase == NULL || LayoutBase == NULL || ButtonBase == NULL)

    {

        return RETURN_FAIL;

    }



    struct Window *windows[WID_LAST];

    Object *objects[OID_LAST];



    struct MsgPort *AppPort = IExec->AllocSysObjectTags(ASOT_PORT, TAG_DONE);



    if ( AppPort != NULL )

    {

        objects[OID_MAIN] = IIntuition->NewObject(NULL, "window.class",

            WA_ScreenTitle, "Window Example",

            WA_Title, "Window Example",

            WA_Activate, TRUE,

            WA_DepthGadget, TRUE,

            WA_DragBar, TRUE,

            WA_CloseGadget, TRUE,

            WA_SizeGadget, TRUE,



            // If on the Workbench screen, this tells window.class that

            // we can handle the iconify/uniconify when changing screens.

            WINDOW_Iconifiable, TRUE,



            WINDOW_AppPort, AppPort,

            WINDOW_Position, WPOS_CENTERMOUSE,

            WINDOW_Layout, IIntuition->NewObject(NULL, "layout.gadget",

                LAYOUT_Orientation, LAYOUT_ORIENT_VERT,

                LAYOUT_SpaceOuter, TRUE,

                LAYOUT_DeferLayout, TRUE,

                LAYOUT_AddChild, IIntuition->NewObject(NULL, "button.gadget",

                    GA_Text, "Click Me",

                TAG_DONE),

           TAG_DONE),

        TAG_DONE);



        if (objects[OID_MAIN] != NULL)

        {

            //  Open the window.

            windows[WID_MAIN] = (struct Window *)IIntuition->IDoMethod(objects[OID_MAIN], WM_OPEN);



            if (windows[WID_MAIN] != NULL)

            {

                // Obtain the window wait signal mask.



                uint32 signal = 0;

                IIntuition->GetAttr(WINDOW_SigMask, objects[OID_MAIN], &signal);



                // Input Event Loop



                BOOL done = FALSE;



                while (!done)

                {

                    uint32 wait = IExec->Wait(signal | SIGBREAKF_CTRL_C);



                    if ( wait & SIGBREAKF_CTRL_C )

                    {

                        done = TRUE;

                        break;

                    }



                    if ( wait & signal )

                    {

                        uint32 result = WMHI_LASTMSG;

                        int16 code = 0;



                        while ((result = IIntuition->IDoMethod(objects[OID_MAIN], WM_HANDLEINPUT, &code)) !=

WMHI_LASTMSG)

                        {

                            switch (result & WMHI_CLASSMASK)

                            {

                                case WMHI_CLOSEWINDOW:

                                    windows[WID_MAIN] = NULL;

                                    done = TRUE;

                                    break;



                                case WMHI_ICONIFY:

                                    IIntuition->IDoMethod(objects[OID_MAIN], WM_ICONIFY);

                                    windows[WID_MAIN] = NULL;

                                    break;



                                case WMHI_UNICONIFY:

                                    windows[WID_MAIN] = (struct Window *)IIntuition->IDoMethod(objects[OID_MAIN],

WM_OPEN);

                                    break;

                            }

                        }

                    }

                }

            }



            /* Disposing of the window object will also close the window if it is

             * already opened, and it will dispose of the layout object attached to it.

             */

            IIntuition->DisposeObject(objects[OID_MAIN]);

        }



    }



    IExec->FreeSysObject(ASOT_PORT, AppPort);



    return RETURN_OK;

}

Chris

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 0:47 #2

Amigans Defender

@nubechecorre

The WID_LAST, OID_LAST etc are to make it easier to define your arrays.


enum {

  OID_MAIN = 0,

  OID_LAST

};



Object *objects[OID_LAST];



objects[OID_MAIN] = NewObject(blah);

nubechecorre

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 9:49 #3

Just can't stay away

Ok but what i don't understand is why there is an oid_last if in the layout of the GUI it isn't used?...

jabirulo

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:03 #4

Just can't stay away

As Chris posted is for defining the array length (remember arrays in C starts from 0, maybe other languages don't):


...

// I have 6 gadgets

enum

{

    GID_MAIN=0,

    GID_INTEGER1,

    GID_INTEGER2,

    GID_DOWN,

    GID_UP,

    GID_QUIT,

    GID_LAST

};



// I have 1 window

enum

{

    WID_MAIN=0,

    WID_LAST

};



// I have 1 object

enum

{

    OID_MAIN=0,

    OID_LAST

};



int main(void)

{

    struct MsgPort *AppPort;

    struct Window *windows[WID_LAST];

    struct Gadget *gadgets[GID_LAST];

    Object *objects[OID_LAST];



    /* make sure our classes opened... */

...

nubechecorre

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:22 #5

Just can't stay away

Ok but where is reported all this? Because i wasn't able to find any documentation about it..

I am talking about Every id_last that are defined inside the enum but are not used in the GUI layout.. And why the object pointer always point to the last enum id if this one (ID_LAST) is never used?

ChrisH

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:30 #6

Home away from home

@nubechecorre Quote:

Ok but what i don't understand is why there is an oid_last if in the layout of the GUI it isn't used?...

It looks like OID_LAST is very needed to me:
Quote:

Object *objects[OID_LAST];

In other words, OID_LAST is used as a count of how many items an array needs to hold all your objects. In the above code, you can use array indexes from 0 to OID_LAST-1.

Author of the PortablE programming language.

nubechecorre

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:42 #7

Just can't stay away

Ok thanks that's the idea that i made on my mind reading and studying the examples.. Sorry for the question but, is there any reference/link about this method and object *object_[last element] inside the Amiga SDK?..

broadblues

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:44 #8

Home away from home

@nubechecorre

It's simply a neat trick to get the size of the array need to hold all the object pointers, gadget pointers or image pointers, depending on what you enum is decribing.

enum {
GAD_ID_ZERO, // = 0
GAD_ID_ONE, // = 1
GAD_ID_TWO, // =2
GAD_ID_LAST // = 3
};

Thus by defining the array

Object * gadgets[GAD_ID_LAST]

you create an array of the correct size, which will always resize (after recompilation) if you add more gadgets,

so your enum becomes

enum {
GAD_ID_ZERO, // = 0
GAD_ID_ONE, // = 1
GAD_ID_TWO, // =2
GAD_ID_THREE, // = 3
GAD_ID_LAST // = 4
};

The array is autmaticall resixed when you recompile your code, this avoids having to calculate the numeber or keep track of the number of gadgets you are using.

I personally always make my last item

GAD_ID_NUMGADS or IMG_ID_NUMIMGS etc to make it more obvious.

It's probably not described in detail in any amiga specific doc as it's a general C prgramming trick.

Blender For OS4.x : Blues : Walker Broad

nubechecorre

Re: Newbie question about ENUM and GUI development

Posted on: 2016/8/7 10:45 #9

Just can't stay away

Most important, thanks to all, now is much clear!!

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