BOOPSI 101

In this section we will explore a simple example of creating, interacting with and disposing a simple BOOPSI object - a requester window. With these simple objects you can see the basic operations that are common to almost all BOOPSI objects. When using BOOPSI gadget objects there may be some changes in syntax (f.e., using SetGadgetAttrs() instead of SetAttrs()), but the concepts remain the same.

Creating an Object

The Intuition functions NewObject() / NewObjectA() create a BOOPSI object using either "stack" of tags or predefined a tag list and returns a pointer to a new BOOPSI object:

Object *object = NewObject(Class *cl, ClassID classID, Tag tag1, ...);
Object *object = NewObjectA(Class *cl, ClassID classID, const struct TagItem *tags);

As mentioned previously (see BOOPSI and Tags), the NewObject() function has a variant that uses predefined tag lists (NewObjectA()), but here we will continue with the more commonly used stack based variant.

In general, BOOPSI objects are "black boxes". This means the inner workings of BOOPSI objects are not visible to the application programmer, so the programmer does not know what goes on inside it. This really means the inner workings of these objects are none of your business. Unless otherwise documented, only use an object pointer as a handle to the object.

To create an object, NewObject() first needs to know whether we are creating an object from a public or private class. Typically any objects created from system gadgets are all public classes. In such cases, the cl argument (a pointer) would be set to NULL and classID argument set to the text name of the class (like "requesterclass" or "string.gadget"). If one wanted to create an object of a private class, the cl argument would be a pointer to that class and the classID would be ignored.

Regardless of whether the tag list is defined elsewhere or within this function call, some list of "tags" is next proivided to define the characteristics of the new object. Each "tag" consists of a pair of values - each with specifically named "attribute" and it's proposed "value". Some general examples of such tags might be:

     GA_Left,         100,
     REQ_TitleText,   "Testing...",
     WA_DragBar,      TRUE,

In the case of our requester example, we can use the NewObject{} function along with a "stack" of "tags" containing basic parameters to create a new requester object like this:

     reqobj = IIntuition->NewObject(NULL,"requester.class",
          REQ_Type,        REQTYPE_INFO,
          REQ_TitleText,   "Requesters Example",
          REQ_BodyText,    buffer,
          TAG_END);

If successful, the variable reqobj will contain a pointer to new a BOOPSI requester object. If unsuccessful, reqobj will be NULL. This is a place for a developer to apply some error trapping when an object couldn't be created - maybe our application ran out of memory? maybe some of the parameters (tags) were invalid?

Once the requester object has been created, we still won't see anything yet. Our new object is waiting in the wings for a BOOPSI message to show itself. This leads us to the next sections where we interact with the object we created.

Passing messages to an Object

To communicate with BOOPSI objects we send "BOOPSI Messages". Unlike traditional AmigaOS "Messages" used by the Exec, ARexx and for interprocess communications, BOOPSI messages are different and frequently rely on tag lists for their content. To "send" a BOOPSI Message to an existing object, we use the IDoMethod function (or its tag list based variant):

ULONG IDoMethod(Object *myobject, ULONG methodID, ...);
ULONG IDoMethodA(Object *myobject, Msg boopsimessage);

The return value is class-dependent. The first argument to both of these functions points to the object that will receive the BOOPSI message.

IDoMethod() then depends on the class and method being used for the contents of the rest of the message. Those elements may include a method name, tags, text or pointers. The class documentation will described those as well as whether the class expects any certain order of tags, etc.

For a simple example, we can ask the BOOPSI requester object reqobj (created above) to show itself by sending this message:

result = IIntuition->IDoMethod( reqobj, RM_OPENREQ, NULL, NULL, NULL );

In this case, the RM_OPENREQ method of the Requester Class expects the elements of its orRequest structure. The class docs point us to a header file that explains we need to start with the MethodID and then pointers to a tag list, window and a screen structures. In our simple example above, we are passing no arguments, so our call has three NULL's for these elements.

When one calls IDoMethod()' with the RM_OPENREQ method on a requester object, the requester appears and the application waits for the user input. Given the simple "information" style requester we created (with default buttons), the result will simply numerically indicate which button was selected by the user.

With the IDoMethodA() variant, all of the above arguments have to be combined into a complete BOOPSI Message structure, boopsimessage. Again the layout of depends on the class and method. Every method's message starts off with a Msg (from <intuition/classusr.h>) and is followed by the class specific tags:

typedef struct {
    ULONG MethodID; /* Method-specific data may follow this field */
} *Msg;

As mentioned above, there are variants of the IDoMethod() functions for specific uses, such as the DoGadgetMethod() function. In that case, the function passes additional information pertinent to GUI gadget objects.

Setting an Object's Attributes

Every BOOPSI object is defined by a number of attributes. In the above example we defined our requester when we created the object with NewObject(). But an object's attributes are not necessarily static. An application can use the SetAttrs() function to change or set other attributes on an object:

     uint32 IIntuition->SetAttrs( Object * object, Tag tag1, ... );
     uint32 IIntuition->SetAttrsA( Object * object, const struct TagItem * tagList );

In each case we have to provide a pointer to our object and then tag pairs with the Attribute identifiers and the replacement values. As an example, we can use the SetAttrs() function to reset the type and contents of our requester object from above and reuse the object to open a second, different requester for the user.

     strcpy(buffer,"default string");
     result = IIntuition->SetAttrs( reqobj,
          REQ_Type,				REQTYPE_STRING,
          REQ_BodyText,			"please enter some text",
          REQS_Buffer,			buffer,
          REQS_MaxChars,			sizeof(buffer) - 1,
          TAG_END);
     result = IIntuition->IDoMethod( reqobj, RM_OPENREQ, NULL, NULL, NULL );

With these changes, we've converted our simple requester with a couple buttons into a string requester. For any attributes we did not reset here, the previous settings or the default values of the class will continue to be used.

Not all object attributes can be set with SetAttrs() and this is dependent on each class. For more information about which attributes can be set in specific classes, see the BOOPSI Class Reference and the class AutoDocs and look for those attributes with a OM_SET listed as an "applicability".

Again there is variant of the SetAttrs() function to be used with BOOPSI GUI gadgets: SetGadgetAttrs().

Getting an Object's Attributes

Just as we can set attributes of an existing BOOPSI object, we also have the ability to get the current settings from a object's attributes. Inquiring about a specific setting is done using the BOOPSI function GetAttr():

uint32 attr = GetAttr(uint32 attrID, Object *object, uint32 *storage);

We start by specifying the attrID is the attribute's identifier we are interested in, we then have to identify object to get the attribute from (object), and finally provide an area that will hold the value of the attribute. This function returns a 0 if the object doesn't recognize or return the attribute, otherwise it returns some non-zero value, the meaning of which depends on the class. In most cases, GetAttr() returns a 1 when it is successful.

In the case of our requester example, there are only a few attributes to which values can be obtained. The following example will obtain the result code from the last use of the object:

     uint32 lastresult;
     result = IIntuition->GetAttr(REQ_ReturnCode, reqobj,&lastresult);

Another example of the GetAttr function would be to retrieve the value a user provided in an Interger type requester. This information could be restrieved like this:

     int32 userInt;
     result = IIntuition->GetAttr(REQI_Number, reqobj,&userInt);

While the simple requester class is not a great example for getting a lot of attributes, BOOPSI provides a second pair of functions that uses taglists for obtaining multiple attributes in one call: GetAttrs() and GetAttrsA:

     uint32 retval = GetAttrs(Object *object, Tag tag1, ...);
     uint32 retval = GetAttrsA(Object *object, struct TagItem *attrs);

As with the previous tag functions mentioned above, these functions are the same except for how the tag list is handled. In the case of each tag pair, the value will be set to the current value in the object queried.

As with setting attributes, not all object attributes are obtainable using the GetAttr() function, depending on each class. For more information about which attributes can be obtained in specific classes, see the BOOPSI Class Reference and the class AutoDocs and look for those attributes with a OM_GET listed as an "applicability".

Unlike when creating and setting attributes on BOOPSI GUI gadgets, there are no GUI gadgets specific versions of the GetAttr family of functions. Instead, the GetAttr functions can also be used to obtain GUI gadget attributes where they are available (see the Class Reference and autodocs).

Disposing of an Object

When an application is finally done with an object, it has to dispose of the object. To dispose of an object, use the Intuition function DisposeObject():

void DisposeObject(Object *obj);

As usual, we use a pointer to our object to indicate the object to be disposed.

In the case of our requester example, we would simply call:

     IIntuition->DisposeObject(reqobj);

In many cases - complex gadget GUI's being the prime example - when a BOOPSI object has connect "child" objects and it is disposed, then all children are also disposed. An example would be a window object and all the gadgets within that window. In any case, you must be careful not to dispose of an object that already been disposed.

What About the BOOPSI Messages and Methods?

In the above sections of this page, the functions used reflect BOOPSI messages and the underlying basic "methods" performed by a BOOPSI object. In the "OOP Overview" section we see how these saw how these common methods are practically universal to all BOOPSI classes. The above functions simply provide a wrapper for those common methods like this:

NewObject()	OM_NEW
SetAttrs()/SetGadgetAttrs()	OM_SET
GetAttr()	OM_GET
DisposeObject()	OM_DISPOSE

These methods are defined on the rootclass level, so all BOOPSI classes inherit them. The Intuition functions that correspond to these methods take care of constructing and sending a BOOPSI message with the appropriate method ID and parameters.

One last function had a more direct relationship to operation and methods of BOOPSI objects - in this case, causing our requester object to present itself :

IDoMethod()

RM_OPENREQ

Of course, in the case of different classes and objects, the method would change with how the IDoMethod function was called on those objects.

Example Program

Below is the complete example program that includes the above excerpts. This program will create a requester object, display a requester with buttons and one with a string gadget and print the results in the shell.

/* Requesters Example
gcc -o Requesters Requesters.c -lauto
quit
*/
 
/*
*
************************************************************
**
** Created by: CodeBench 0.31 (20.5.2013)
**
** Project: OS4ex-Requesters
**
** A simple requester.class example used to demonstrate functionality.
**
** File: Requesters
**
** Date: 20-04-2013 20:43:23
**
** Version:   02
**
************************************************************
*
*/
 
/*		includes
 */
#include <exec/exec.h>
#include <dos/dos.h>
#include <intuition/intuition.h>
#include <classes/requester.h>
 
#include <proto/intuition.h>
#include <proto/exec.h>
#include <proto/dos.h>
#include <proto/requester.h>
 
#include <string.h>
 
/*		declarations
 */
Object *reqobj;
struct orRequest reqmsg;
char buffer[100];
uint32 result = 0;
 
int main()
{
 
	/*		create a new requester object
	 */
	strcpy(buffer,"Welcome to your\nfirst BOOPSI requester");
 
	reqobj = IIntuition->NewObject(NULL,"requester.class",
		REQ_Type,				REQTYPE_INFO,
		REQ_TitleText,			"Requesters Example",
		REQ_BodyText,			buffer,
		TAG_END);
 
	// Was the requester object created?
	if (reqobj)
	{
		IDOS->Printf("   Requester object created\n");
		/*		tell the object to show itself
		 */
		result = IIntuition->IDoMethod( reqobj, RM_OPENREQ, NULL, NULL, NULL );
		// How did things go?
		if (result)
			IDOS->Printf("  Req #1 - result code = %ld\n",result);
		else
			IDOS->Printf("   Req #1 - result = 0\n");
 
		/*		reset object characteristics
		 */
 
		strcpy(buffer,"default string");
		result = IIntuition->SetAttrs( reqobj,
			REQ_Type,				REQTYPE_STRING,
			REQ_BodyText,			"please enter some text",
			REQS_Buffer,			buffer,
			REQS_MaxChars,			sizeof(buffer) - 1,
			TAG_END);
 
		/*		tell object to show itself again
		 */
		result = IIntuition->IDoMethod( reqobj, RM_OPENREQ, NULL, NULL, NULL );
		// Did we get a good response?
		if (result>0)
		{
			IDOS->Printf("  Req #2 - result code = %ld\n",result);
			IDOS->Printf("  Req #2 - result text = %s\n",buffer);
		}
		else
			IDOS->Printf("   Req #2 - result = 0\n");
 
		/*		Lets check some object attributes
		 */
		uint32 lastresult;
 
		result = IIntuition->GetAttr(REQ_ReturnCode, reqobj,&lastresult);
		// Did we get some value?
		if (result>0)
			IDOS->Printf("   Last result code = %ld\n",lastresult);
		else
			IDOS->Printf("   This result = 0\n");
 
		/*		Dispose of our requester object
		 */
		IIntuition->DisposeObject(reqobj);
	}
	else
		IDOS->Printf("   ERROR: Failed to create Requester object\n");
 
	return RETURN_OK;
}