System for passing messages between source object and target object utilizing generic code in source object to invoke any member function of target object by executing the same instructions

A method and system for interconnecting software components. In a preferred embodiment, the present invention instantiates an event object. The event object includes message information describing the message and a dispatching member function for invoking a member function of a target object passing the message information. A message is passed by invoking the dispatching member function of the event object passing an identifier to a target object and an identifier of a member function of the target object. The dispatching member function invokes the identified member function of the identified target object passing the event information as an actual parameter. The event object is preferably of a derived class that inherits a base class. The base class provides common event behavior, while the derived class provides behavior specific to a type of message.

TECHNICAL FIELD 
The present invention relates generally to a computer system for visual 
programming, and more specifically, to a method and system for 
interconnecting visual components and passing messages between connected 
components. 
BACKGROUND OF THE INVENTION 
Visual programming is a computer programming technique that allows for 
rapid development of visually oriented programs (visual programs). FIG. 1 
is a diagram illustrating a sample operation of a visual program. The 
visual program is a temperature converter, which converts Fahrenheit to 
Centigrade, and vice versa. The Fahrenheit scroll bar 101 is used to set 
the Fahrenheit value to between 0 and 100 degrees as indicated by the 
position of the Fahrenheit slider 103. The Fahrenheit display 102 displays 
the numeric Fahrenheit value represented by the position of the Fahrenheit 
slider. The Centigrade scroll bar 111 is used to set the Centigrade value 
between 0 and 100 degrees as indicated by the Centigrade slider 113. The 
Centigrade display 112 displays the numeric Centigrade value represented 
by the position of the Centigrade slider. In operation, when the 
Fahrenheit slider is moved by a user, the Centigrade slider is 
automatically moved to the corresponding Centigrade position and the 
Fahrenheit and Centigrade displays are updated. Conversely, when the 
Centigrade slider is moved by a user, the Fahrenheit slider is 
automatically moved to the corresponding Fahrenheit position and the 
Centigrade and Fahrenheit displays are updated. 
Visual programming allows various components (e.g., a scroll bar) to be 
interconnected visually to effect the program behavior. A visual 
programming environment typically includes a list of predefined components 
that can be interconnected to create a visual program. Each component may 
include input and output ports and a visual interface. When creating a 
visual program, a programmer specifies the visual components and their 
location on the display. The programmer also specifies the interconnection 
between various ports. The components pass values through these 
connections. FIG. 2 is a block diagram illustrating a scroll bar 
component. The scroll bar component 201 receives messages from the 
operating system (e.g., mouse down) and controls the display of a scroll 
bar. The scroll bar also provides an input port 203 and an output port 
202. The input port is used to receive a value indicating a new position 
of the slider and the output port is used to send a value indicating a new 
slider position. The scroll bar can be connected to other components 
through its ports. 
FIG. 3 is a diagram illustrating a scroll bar connected to a display 
component. A display component 301 has one input port 303 for receiving a 
value. The display component controls the displaying of the value that it 
receives. The output port 202 of the scroll bar component 201 is connected 
to the input port 303 of the display component. In operation, whenever the 
scroll bar slider is moved, a value indicating the new position of the 
slider is sent from the scroll bar component to the display component. The 
display component receives this value and updates its display accordingly. 
Although prior references have described general visual programming 
environments, visual programming is not widespread because of the 
inefficiencies of visual programs. For example, visual programs often 
execute in an interpretive mode that results in unacceptably slow 
performance. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and system 
that allows for creation of efficient visual programs. 
It is another object of the present invention to provide a method and 
system that shields component developer from the details of the connecting 
of components and the passing of values between components. 
These and other objects, which will become apparent as the invention is 
more fully described below, are obtained by an improved method and system 
for sending messages between components. In a preferred embodiment, the 
present invention instantiates an event object. The event object includes 
message information describing the message and a dispatching member 
function for invoking a member function of a target object passing the 
message information. A message is passed by invoking the dispatching 
member function of the event object passing an identifier to a target 
object and an identifier of a member function of the target object. The 
dispatching member function invokes the identified member function of the 
identified target object passing the event information as an actual 
parameter. The event object is preferably of a derived class that inherits 
a base class. The base class provides common event behavior, while the 
derived class provides behavior specific to a type of message.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides a method and system for connecting 
components and passing of messages (events) between components. In a 
preferred embodiment, each component may provide multiple input ports and 
output ports. Each output port sends a message corresponding to a 
particular type of event; each input port receives a message corresponding 
to a particular type of event. A component that sends a message is 
referred to as a source, and a component that receives the message is 
referred to as the target. In a preferred embodiment, each component has 
an associated run-time class and editor class. The editor class provides 
component-specific behavior to assist in creating a visual program. The 
run-time class provides the component behavior when the visual program 
executes. A visual programming system controls the development of visual 
programs by instantiating objects of the editor classes and controls the 
run-time execution by instantiating objects of the run-time class. As 
described below, the present invention provides a mechanism in which 
messages are efficiently passed between components. In the following, a 
preferred embodiment of the present invention is described using 
well-known object-oriented terminology and terminology of the C++ 
programming language. 
FIG. 4 is a diagram illustrating visual programming of the present 
invention. To generate a visual program to implement a temperature 
converter, a programmer would position a Fahrenheit scroll bar 401, a 
Fahrenheit display 430, a Centigrade scroll bar 420, and a Centigrade 
display 440. The programmer would also position an FtoC calculator 460, 
which converts a Fahrenheit value to a Centigrade value, and a CtoF 
calculator 450, which converts a Centigrade value to a Fahrenheit value. 
In one embodiment, the components are selected from an extendible list of 
available components. The programmer then connects the components through 
their ports. The connections 412.fwdarw.461 and 412.fwdarw.431 indicate 
that when the Fahrenheit scroll bar is changed (e.g., slider moved), the 
new value is sent to the FtoC calculator and the Fahrenheit display. The 
connection 462.fwdarw.421 indicates that when the FtoC calculator 
calculates a new Centigrade value, the new value is sent to the Centigrade 
scroll bar. The connections 422.fwdarw.441 and 422.fwdarw.451 indicate 
that when the Centigrade scroll bar is changed, the new value is sent to 
the CtoF calculator and the Centigrade display. The connection 
452.fwdarw.411 indicates that when the CtoF calculator calculates a new 
Fahrenheit value, the new value is sent to the Fahrenheit scroll bar. In 
one embodiment, the components are connected by entering a connect mode 
and selecting the source and target of each connection. 
The visual programming system instantiates an object of the run-time class 
for each component selected by the programmer. FIG. 5 is a diagram 
illustrating the instantiated objects for the temperature converter. The 
FScrollbar object 501 corresponds to the Fahrenheit scroll bar component, 
the CScrollbar object 502 corresponds to the Centigrade scroll bar 
component, the FDisplay object 503 corresponds to the Fahrenheit display 
component, the CDisplay object 504 corresponds to the Centigrade display 
component, the FtoC object 505 corresponds to the FtoC calculator 
component, and the CtoF object 506 corresponds to the CtoF calculator 
component. Each of these objects implements the display and control of the 
corresponding component. The directed arcs indicate the direction of the 
connections, that is, from an output port to an input port. 
Each component may send messages to other components corresponding to 
different types of events. For example, a scroll bar may send a message to 
indicate a changed value event has occurred and another message to 
indicate a scroll down has occurred. Each type of event has its own output 
port. Also, input ports are designated to receive only certain types of 
events. For example, an output port that sends messages relating to a 
scroll up event can only be connected to an input port that expects a 
message in the same format as a scroll up message. 
A source object (corresponding to a source component) sends a message 
(communicates the occurrence of an event) by invoking a member function of 
a target object (corresponding to a target component). Each input and 
output port is preferably associated with a function member of the 
run-time object. For example, a scroll bar object may have a function 
member named ValueIn corresponding to an input port for receiving a new 
value and a function member named ValueOut corresponding to an output port 
for sending a new value. In operation, the member function ValueOut is 
invoked whenever a change in the value for the scroll bar occurs, e.g., 
when the slider is moved. The member function ValueOut invokes the target 
member function corresponding to each input port to which it is connected. 
The invoked target member function then processes the value information 
which is passed as a parameter. 
In a preferred embodiment, message information (e.g., new value) is 
encapsulated in an object of an event class. The source member function 
corresponding to an output port creates an event object and stores the 
event information in the event object. The source member function effects 
the invocation of a notify member function of a target object passing the 
event object and a pointer to the target member function. The notify 
member function invokes a dispatching member function of the event object 
passing a pointer to the target object and a pointer to the target member 
function. The dispatching member function invokes the target member 
function passing the stored information as a parameter. In a preferred 
embodiment, different implementations of event objects are used to 
represent different function prototypes (parameter list) of target member 
functions. Each class of event object contains information that is passed 
to a target member function according to the function prototype. Thus, 
each source member function invokes target member functions with the same 
prototype. 
In a preferred embodiment, each run-time class inherits the class CObject. 
The class CObject tracks the connections and controls the sending of 
messages. The class CObject is referred to as a connection manager. In 
this way, run-time classes that implement component behavior can be 
developed without detailed knowledge of the implementation of the class 
CObject. Moreover, run-time objects implemented by different developers 
can cooperatively interact. FIG. 6 is a table containing a listing of the 
connections for the for the temperature converter program. The class 
CObject includes an array (connectionArray) that contains the connections 
for each output port of the run-time object. Each entry of the connection 
array contains an identifier of the output port of the source object, an 
identifier of the target object, and an identifier of the input port of 
the target object. For example, the connection array for the FScrollbar 
object contains two entries: 
(Out1, FDisplay, In1) and (Out1, FtoC, In1) 
"Out1" identifies the output port, "FDisplay" and "FtoC" identify the 
target objects, and "In1" identifies the input port of the target objects. 
When an event occurs for a particular output port, the source object 
instantiates an event object and invokes an inform targets member function 
of the class CObject (connection manager) identifying the output port. The 
output port is preferably identified by a pointer to a member function 
(source member function) of the source object. The inform targets member 
function sends an appropriate message to each target object as indicated 
by the connection array for the source object. The input port is 
preferably identified by a pointer to a member function (target member 
function) of the target object. The connection manager sends the message 
to the target object by invoking a notify member function of the target 
object passing a pointer to the target member function and an event 
object. The event object contains actual parameters for the target member 
function. The notify member function invokes a dispatch member function of 
the event object passing a pointer to the target member function and a 
pointer to the target object. The dispatch member function formats the 
actual parameters and invokes the target member function of the target 
object passing the actual parameters. 
Code Table 1 contains pseudocode for the class CObject. 
__________________________________________________________________________ 
Code Table 1 
class CONNECTION 
{ CObject *ptarget; 
ULONG pmftarget; 
ULONG pmfsource; 
class CObject 
{ 
boolean isRecursing; 
CONNECTION 
connectionArray10!; 
int connectionCount; 
virtual boolean Notify Event (CEvent *pevent, CObject *psource, ULONG 
pmftarget); 
boolean InformTargets(CEvent *pevent, ULONG pmfsource); 
void 
AddTarget(CObject *ptarget, ULONG pmftarget, ULONG 
pmfsource); 
virtual void 
Serialize(CArchive &ar); 
virtual VOID 
WriteConnectionArray(CArchive &ar); 
virtual VOID 
ReadConnectionArray(CArchive &ar); 
virtual VOID 
SerializeObjectData(CArchive &ar); 
}; 
BOOL CObject::NotifyEvent (CEvent *pevent, CObject *psource, ULONG 
pmftarget) 
{ 
BOOL ret; 
if (isRecursing) return FALSE; 
isRecursing = TRUE; 
if (pevent -&gt; IsKindOf(CValueEvent)) 
ret = ((CValueEvent*)pevent)-&gt;Dispatch(psource, this, 
pmftarget); 
else if 
. 
. 
. 
else return FALSE; 
isRecursing = FALSE; 
return ret; 
} 
BOOL CObject::InformTargets(CEvent *pevent, ULONG pmfsource) 
{ 
for (i = 0; i &lt; connectionCount; i++) 
{ 
if (connectionArrayi!.pmfsource==pmfsource) 
connectionArrayi!.pmftarget-&gt;NotifyEvent(pevent, this, 
connectionArrayi!.pmftarget); 
} 
} 
void CObject::AddTarget(CObject *ptarget, ULONG pmftarget, ULONG 
pmfsource) 
{ 
i = connectionCount++; 
connectionArrayi!.ptarget = ptarget; 
connectionArrayi!.pmftarget = pmftarget; 
connectionArrayi!.pmfsource = pmfsource; 
} 
__________________________________________________________________________ 
The programming system adds connections to a run-time object by invoking 
the member function AddTarget provided by the connection manager. The 
programming system invokes the AddTarget member function of the source 
object whenever a programmer connects two objects. The member function 
AddTarget is passed a pointer to the target object, a pointer to the 
target member function (representing the input port), and a pointer to a 
source member function (representing the output port). The member function 
AddTarget adds an entry to the connectionArray of the source object 
corresponding to the passed parameters. In a preferred embodiment, the 
connections are stored not as data members of the CObject, but rather are 
stored in a heap that is shared by all run-time objects. In this way, the 
storage overhead for each object can be minimized. 
A message is sent to a target object in the following manner. The source 
object instantiates an event object and stores event information in the 
event object. The source object invokes the member function InformTargets 
of its connection manager passing the event object and a pointer to the 
source member function. For each connection for that output port (source 
member function), the connection manager invokes the member function 
NotifyEvent of target object passing the event object, a pointer to the 
target member function, and a pointer to the source object. The member 
function NotifyEvent invokes the member function Dispatch of the event 
object passing a pointer to the source object, a pointer to the target 
object, and a pointer to the target member function. The member function 
Dispatch invokes the target member function of the target object passing 
the stored event information as actual parameters. An event object 
encapsulates the message information in a way that is transparent to the 
connection manager. Thus, the connection manager can control the invoking 
of target member functions passing arbitrary parameters. 
FIG. 7 is a flow diagram illustrating the flow of control of sending a 
message from a source object to a target object. A source member function 
710-714 of the source object instantiates an event object in step 711. In 
step 712, the source member function stores the event information in the 
event object. In step 713, the source member function invokes the member 
function InformTargets of the connection manager passing a pointer to the 
event and the source member function. In step 721, the member function 
InformTargets loops determining which entries in the connection array 
correspond to the source member function. When an entry is found, the 
member function InformTargets invokes the member function NotifyEvent of 
the target object passing a pointer to the event, a pointer to the source 
object, and a pointer to the target member function. In step 731, the 
member function NotifyEvent of the target object invokes the member 
function Dispatch of the event passing a pointer to the source object, a 
pointer to the target object, and pointer to the target member function. 
In step 741, the member function Dispatch invokes the target member 
function passing the event information stored in the event object. The 
target member function processes the event information in step 751. The 
target member function then returns, which causes the member functions 
Dispatch, NotifyEvent, and InformTargets to return to the execution of the 
source member function. 
The use of an event object allows the connection manager to invoke input 
member functions with arbitrary parameters. Each prototype for a input 
member function has its own implementation of the event class to handle 
the event. The source object instantiates the appropriate class of event 
object. For example, the input member function ValueIn is passed an 
integer. Thus, an event class is implemented that contains an integer data 
member to store the value. The member function Dispatch of the event class 
invokes a passed target member function passing the stored value. An event 
class may be implemented for each different prototype of a target member 
function. For example, if the event information includes both an integer 
and a string, then an event class can have a data member for the integer 
and another for the string. The member function Dispatch of the event 
class invokes a passed target member function passing the integer and the 
string as parameters. 
Code Table 2 contains pseudocode that describes the event classes. Each 
event class derives from the class CEvent. The event class CIntEvent is 
used to pass information stored as an integer to a target member function. 
The member function Dispatch is passed a pointer the target object and a 
pointer to the member function. The member function Dispatch invokes the 
target member function by the following statement: 
(ptarget.fwdarw.*(LongToMember (pmftarget)))(numValue) 
The event class CActionEvent is used to pass messages with no corresponding 
data, and the event class CStringEvent is used to pass messages with 
string data. 
__________________________________________________________________________ 
class CEvent 
public: 
CEvent( ); 
virtualBOOL Dispatch(CObject *psource, CObject *ptarget, ULONG 
pmftarget)=0; 
} 
class CActionEvent: public CEvent 
{ 
public: 
virtual BOOL Dispatch (CObject *psource, CObject *ptarget, ULONG 
pmftarget) 
{(ptarget-&gt;*(LongToMemberpmf)))( )}; 
} 
class CIntEvent: public CEvent 
{ 
public: 
INT numValue; 
virtual BOOL Dispatch (CObject*psource, CObject *ptarget, ULONG 
pmftarget) 
{(ptarget-&gt;*(LongToMember(pmftarget)))(numValue)}; 
} 
class CStringEvent : public CEvent 
{ 
public: 
STRING string Value; 
virtual BOOL Dispatch (CObject *psource, CObject *ptarget, ULONG 
pmftarget); 
{(ptarget-&gt;*(LongToMember(pmftarget)))(stringValue)}; 
} 
__________________________________________________________________________ 
Code Table 3 contains pseudocode for a sample scroll bar object 
corresponding to a scroll bar component. The scroll bar object is defined 
by class CScrollbar, which inherits the connection manager (class 
CObject). The class contains data members to store the current value of 
the scroll bar, a large and small increment for the scroll bar, and the 
minimum and maximum values for the scroll bar. The class also contains the 
member function to set and retrieve the current value, to receive messages 
from the parent window of that scroll bar, and to effect various scroll 
bar behaviors. The scroll bar component has an input function member 
(value) with one parameter and an output function member (value) with no 
parameters. 
The constructor CScrollbar registers the scroll bar with the operating 
system and initializes its data members. The member function 
HandleParentMsg receives messages from the parent window and dispatches 
the message. For example, if the member function HandleParentMsg is passed 
a message that the scroll bar event line up (SB.sub.-- LINEUP) has 
occurred, then the member function invokes the member function LineUp. The 
member function LineUp instantiates a CActionEvent object, sets a pointer 
to the member function LineUp, and invokes the member function 
InformTargets of the connection manager. The member function LineUp then 
invokes the member function value passing a new value for the scroll bar. 
The member function value receives the new value. If the new value is 
different than the current value, then the member function adjusts the 
slider, instantiates a CIntEvent object, sets the event object to the new 
value, sets a pointer to the member function value (to identify the source 
member function), and invokes the member function InformTargets of the 
connection manager. 
The member function minimum illustrates a member function of an object that 
does not cause a message to be sent to target objects, that is, it does 
not correspond to an output port. The member function minimum, however, 
may correspond to an input port. In one embodiment, a member function 
could correspond to both an input and an output port (a bidirectional 
port). The member function can be invoked to receive a message and then 
send a message to other target objects. 
In a preferred embodiment, the present invention is implemented to execute 
under the Windows operating system developed by Microsoft Corporation. The 
Windows operating system is described in "Programming Windows" written by 
Charles Petzold and published by Microsoft Corporation, which is hereby 
incorporated by reference. 
__________________________________________________________________________ 
Code Table 3 
__________________________________________________________________________ 
class CScrollbar: CObject, CWindow 
INT m.sub.-- largeChange; 
INT m.sub.-- smallChange; 
INT m.sub.-- value; 
INT m.sub.-- minimum; 
INT m.sub.-- maximum; 
BOOL m.sub.-- isVert; 
CScrollBar( ); 
CScrollBar(const VRect &pos, CWindow *parent, boolean isVert); 
virtual INT 
largeChange( ); 
virtual VOID 
largeChange(INT); 
virtual INT 
smallChange( ); 
virtual VOID 
smallChange(INT); 
virtual INT 
value( ); 
virtual VOID 
value(INT); 
virtual INT 
minimum( ); 
virtual VOID 
minimum(INT); 
virtual INT 
maximum( ); 
virtual VOID 
maximum(INT); 
virtual VOID 
lineUP( ); 
virtual VOID 
lineDown( ); 
virtual VOID 
pageUP( ); 
virtual VOID 
pageDown( ); 
virtual LONG 
HandleParentMsg(HWND hwnd, unsigned wm, WORD wParam, LONG 
1Param); 
} 
CScrollBar::CScrollBar(const VRec &pos, CWindow *parent, BOOL isVert) 
DWORD style; 
if(isVert) 
style = WS.sub.-- CHILD .vertline. SBS.sub.-- VERT; 
else 
style = WS.sub.-- CHILD .vertline. SBS.sub.-- HORZ; 
m.sub.-- isVert = isVert; 
CWinWindow::Init( 
patent, 
NULL, 
0L, 
"SCROLLBAR", 
**, 
style, 
pos.left, 
pos.top, 
pos.right - pos.left, 
pos.bottom - pos.top, 
NULL, 
NULL); 
smallChange(1); 
largeChange(10); 
minimum(0); 
maximum(100); 
value(0); 
} 
VOID CScrollBar::lineUp( ) 
{ 
CActionEvent evt; 
VOID (ScrollBar::*mfp)( ) = &CScrollBar::lineUp; 
InformTarget(&evt; MemberToLong(mfp)); 
value(m.sub.-- value-m.sub.-- smallChange); 
} 
VOID CScrollBar::value(INT theValue) 
{ 
if(theValue &lt; m.sub.-- minimum) 
theValue = m.sub.-- minimum; 
if (theValue &gt; m.sub.-- maximum) 
theValue = m.sub.-- maximum; 
if (m.sub.-- value | = theValue) 
{ 
m.sub.-- value = theValue; 
if (m.sub.-- hwnd |= NULL) 
Set ScrollPos(GetHwnd( ), SB.sub.-- CTL, m.sub.-- value, 
TRUE): 
CIntValue numEvent; 
INT (CScrollBar::*mfp)( ) = CScrollBar::value; 
numEvent.numValue = m.sub.-- value; 
Inform Targets(&numEvent, (ULONG)MemberToLong(mfp))); 
} 
} 
VOID CScrollBar::minimum(INT theMinimum) 
{ 
m.sub.-- minimum = theMinimum; 
if(m.sub.-- hwnd |= NULL) 
SetScrollRange(GetHwnd( ), SB.sub.-- CTL, m.sub.-- minimum, m.sub.-- 
maximum, TRUE); 
if(m.sub.-- value &lt; the Minimum) 
value(theMinimum); 
} 
LONG ScrollBar::HandleParentMsg( 
HWND hwnd, 
unsigned 
wm, 
WORD wParam, 
LONG 
1Param) 
{ 
switch(wm) 
{ 
case WM.sub.-- HSCROLL: 
case WM.sub.-- VSCROLL: 
switch)(wParam) 
{ 
case SB.sub.-- LINEUP: 
lineUp( ); break; 
case SB.sub.-- LINEDOWN: 
lineDown( ); break; 
case SB.sub.-- PAGEUP: 
pageUp( ); break; 
case SB.sub.-- PAGEDOWN: 
pageDown( ); break; 
case SB.sub.-- TOP: 
value(minimum( )); break; 
case SB.sub.-- BOTTOM 
value(maximum( )); break; 
case SB.sub.-- THUMBTACK: 
case SB.sub.-- THUMBPOSITION: 
value(LOWORD(1Param)); break; 
case SB.sub.-- ENDSCROLL: 
break; 
} 
default break; 
} 
return CWinWindow::HandleParentMSG(*hwnd, wm, w/Param, 1Param); 
} 
__________________________________________________________________________ 
In a preferred embodiment, the programming system persistently stores the 
run-time objects of a visual program. The programing system maintains a 
pointer to each run-time object corresponding to a component. To store the 
program, the programming environment invokes a member function Serialize 
(provided by the connection manager of each object). The member function 
Serialize writes the connection array to the persistent storage and 
invokes the member function SerializeObjectData to write the object 
specific data to the persistent storage. The member function 
SerializeObjectData of the connection manager would typically be 
overridden by the run-time object corresponding to the component. For 
example, the member function SerializeObjectData for the scroll bar object 
writes each data member to persistent storage. Similarly, each object has 
corresponding member functions to retrieve the persistent stored data. 
When storing and retrieving data, the programming system needs to map the 
memory address of each pointer to its persistently stored object data. 
When the object data is retrieved, the pointers in the connection array 
need to be mapped to their new memory locations. 
In a preferred embodiment, each component has a corresponding editor object 
which controls the placement, movement, and connection to the component. A 
standard interface (CEditor) to the editor object is provided. The CEditor 
object provides a standard mechanism (1) for displaying the available 
ports and the current connections, (2) for selecting an available port, 
(3) for connecting a port to another port, and (4) for moving the 
component. The implementor of a component preferably implements an editor 
object that inherits the CEditor interface. When a programmer selects a 
component, the programming system instantiates both the run-time object 
and an editor object for the component. 
FIG. 8 is a block diagram of data structures of a CEditor object. The 
CEditor object 802 contains a pointer to a list of available ports 
(mPortList), a pointer to a user interface editor object (mEditorUI), a 
pointer to the run-time object corresponding to the component (mSubject), 
a pointer to a list of child editor object (mChildEditors), and a pointer 
to a parent editor (mParent). Each port is described by a CEditPort object 
808. A CEditPort object contains a pointer to the associated CEditor 
object (mOwnerEditor), a pointer to a list of input ports to which the 
port is connected (mConnectedPorts), status information (mStatus), and 
pointer to member functions identifying the input and output portions of 
the port (mValueIn and mValueOut) as pointers to member functions. The 
CEditorUI object 812 contains member functions to control moving the 
component on the display and displaying available ports and connections. 
A component may contains child components. For example, a window component 
(parent component) may contain a scroll bar component. The CEditor object 
for the window contains pointers to each child CEditor object. 
The visual programming environment tracks the first level of parent 
components. Each CEditor object tracks its child CEditor objects. When an 
event occurs (e.g. mouse button down), the programming environment passes 
the event to the appropriate first level component. The first level 
component is responsible to passing the event on the appropriate child 
component. 
Code Table 4 is pseudocode for the class CEditor. The CEditer class 
inherits the CObject class. This inheritance allows connections between 
CEditor objects to be controlled by the connection manager. The CEditor 
objects are, thus, connected in a manner similar to the way the run-time 
objects are connected. The CEditor object includes a constructor and 
member function to delete an object. 
______________________________________ 
Code Table 4 
______________________________________ 
class CEditor: 
public CObject 
public: 
CEditor(CEditor* pEditor, CObject* pSubject); 
virtual VOID ObjectDeleted(CObject* object); 
virtual VOID PortChanged(CEditport* port); 
VString mName; 
private: 
CEditPortListPtr mportList; 
CEditorUIPtr mEditorUI; 
CobjectPtr mSubject; 
CEditorListPtr mChildEditors; 
CEditorPtr mParent; 
}; 
VOID CEditor: ObjectDeleted(CObject* object) 
{ 
for each CEditPort port1 in mPortList 
if (port1 is connected) 
for each CEditPort port2 in mConnectedPorts of port1 
if(port2.mSubject == object) 
port1-&gt;Disconnect(port2) 
RemoveTarget(object); 
mSubject-&gt;RemoveTarget(object); 
for each CEditorUI eui in mEditorUIList 
eui-&gt;RemoveTarget(object); 
}; 
______________________________________ 
Code Table 5 contains pseudocode defining CEditorUI class. The CEditorUI 
class provides a standard mechanism for editing connections between 
components and movement of components. When a programmer selects to add a 
component to a visual program, the programming system instantiates the 
object, an CEditorUI for the object, and a CEditor object for the object. 
In a preferred embodiment, the programmer can move a component by clicking 
on the component. A tracker box is drawn and the user can then drag the 
component to a new position. 
______________________________________ 
Code Table 5 
______________________________________ 
class CEditorUI: public CObject; CWindow 
public: 
virtual void 
Draw(const VRect& rectUpdate); 
virtual BOOL 
OnMouseStart(CUserEvp *, VPoint, INT, INT); 
virtual BOOL 
OnMouseDrag(CUserEvp *, VPoint, BOOL); 
virtual BOOL 
OnMouseEnd(CUserEvp *, VPoint, BOOL); 
virtual void 
Positionchange( ); 
BOOL showTracker; 
VPoint startSize; 
VPoint startPoint; 
WORD dragMode; 
virtual BOOL MakeStdUI(CEditor*, CWindow*); 
virtual BOOL NotifyEvent(CEvent* ev, 
CObject* sender, 
ULONG action); 
CPopMenuPtr m.sub.-- popup; 
CPropertyDialogPtr 
m.sub.-- dialog; 
private: 
CEditorPtr mEditor; 
BOOL mIsActive; 
}; 
______________________________________ 
The programming system invokes the member function Draw to request the 
component to draw a tracker box. The programming system invokes the member 
function OnMouseStart to indicate that object is being selected, the 
member function OnMouseDrag to indicate the new position of the tracker, 
and the member function OnMouseEnd to indicate that the tracking is 
complete. The member function OnMouseEnd invokes the member function 
PositionChange to pass the new position to the CEditorUI object that is 
specific to the component (e.g., scroll bar). 
The member function MakeStdUI initializes a standard user interface for the 
component. The standard user interface includes a menu for selecting to 
delete the component, to move or size the component, or to change 
properties of the component. The CEditorUI provides a standard dialog for 
displaying available ports and current connections. For example, a list of 
available ports would be 
______________________________________ 
Name Type Input Member 
Output Member 
______________________________________ 
Position 
CIntEvent 6 7 
Pageup CActionEvent 
11 12 
______________________________________ 
Code Table 6 contains pseudocode describing the CEditPort class. This class 
provides member functions to manage the actual connection between 
components. When two ports are selected for connection, the programming 
system invokes the member function Connect of the output port passing the 
input port. The member function Connect adds the target object to the 
connection array of the source object and adds the input port to the list 
of connections for the editor object. 
______________________________________ 
Code Table 6 
______________________________________ 
class CEditPort: public CObject 
public: 
virtual BOOL Connect(CEditPort* OtherPort); 
virtual BOOL Disconnect(CEditPort* OtherPort); 
private: 
VString mName; 
CEditorPtr mOwnerEditor; 
CObjectPtr mSubject; 
CEditPortListPtr mConnectedPorts; 
BOOL mIsConnected: 1; 
BOOL mIsOutput: 1; 
BOOL mlsInput: 1; 
BOOL mCanRead: 1l; 
BOOL mCanWrite: 1; 
CObjectPtr mValueIn; 
CObjectPtr mValueOut; 
}; 
BOOL CEditPort::Connect(CEditPort* OtherPort) 
{ 
mSubject-&gt;AddTarget( 
OtherPort-&gt;mSubject, 
OtherPort-&gt;MValueIn, 
this-&gt;MValueOut); 
mIsConnected = TRUE; 
mConnectedPorts-&gt;Add(OtherPort); 
return TRUE; 
} 
______________________________________ 
Code Table 7 contains pseudocode for an implementation of the CEditor class 
for a scroll bar component. The implementation provides a constructor for 
the CEScrollBar class that inherits the CEditor class. The Constructor 
instantiates a CEditPort object for each port for the scroll bar 
component. In this example, the ports are "value" and "LineUp." The port 
value is a bidirectional port, that is, the member function value can be 
connected to an input and output port. The constructor also creates a 
CEScrollBarUI object. Code Table 8 contains pseudocode for the 
EScrollBarUI class. 
______________________________________ 
Code Table 7 
class CEScrollBar: CEditor 
{ CESCrollBar(CEditor* pParentEditor, 
CWindow* pParentWindow, 
CObject* pSubject); 
CEScrollBar::CESCrollBar(CEditor* pParentEditor, 
CWindow* pParentWindow, 
CObject* pSubject) 
: CEditor(pParentEditor, pSubject) 
{ 
CEditPort*pp; 
void (CScrollBar::*mfp3)( ); 
name(""); 
{ 
INT(CScrollBar::*mfp1( ) 
= &CScrollBar::value; 
void (CScrollBar::*mfp2)(INT) 
= &CScrollar::value; 
pp = new CNumEditport(this, "Value"); 
pp-&gt;isOutput(TRUE); 
pp-&gt;valueOut((CObject*)MemberToLong(mfp1)); 
pp-&gt;isInput(TRUE); 
pp-&gt;valueIn((CObject*)MemberToLong(mfp2)); 
pp-&gt;canRead(TRUE); 
pp-&gt;canWrite(TRUE); 
portList( )-&gt;Add(pp); 
} 
pp = new CEditPort(this, "Line Up"); 
pp-&gt;isInput(TRUE); 
pp-&gt;valueIn((CObject*)MemberToLong(mfp3 = 
&CScrollBar::lineUp)); 
portList( )-&gt;Add(pp); 
CEScrollBarUI* ui = new CEScrollBarUI(this, 
pParentWindow); 
editorUIList(new CEditorUIList); 
editorUIList( )-&gt;Add(ui); 
} 
Code Table 8 
Class CEScrollBarUI: CEditorUI 
{CEScrollBarUI(CEditor*,CWindow*)} 
CEScrollBarUI::CEScrollBarUI( CEditor* pEditor, 
CWindow* pParentWindow) 
{ 
editor(pEditor); 
parent(pParentWindow); 
CObject*po = editor( )-&gt;subject( ); 
position(((CWindow*)po)-&gt;position()); 
MakeStdUI(pEditor, pParentWindow); 
} 
______________________________________ 
FIG. 9 is a block diagram illustrating a computer system for implementing 
the present invention. The computer system 901 includes central processing 
unit 902, memory 903, storage 904, display 905, and input device 906. In a 
preferred embodiment, objects are instantiated in memory and persistently 
stored to storage. Visual programs output data to the display and input 
data from the input device. 
Although the present has been described in terms of a preferred embodiment, 
it is not intended that the invention be limited to this embodiment. 
Modifications within the spirit of the invention will be apparent to those 
skilled in the art. The scope of the present invention is defined by the 
claims which follow.