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NEW( ) |
Create New Object |
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1. |
Create Object: |
NEW(class$[,param1[$], param2[$],...] [ FOR dependency][,ERR=stmtref] ) |
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2. |
Clone Object: |
NEW(obj_id [ FOR dependency ][,ERR=stmtref] ) |
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class$ |
Object identifier of an existing Object. The cloning process does not run the ON_CREATE for the new clone nor provide access to files from the original. |
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dependency |
Other object, window, file, control or such on which this object is dependent. If this other item is deleted from the system, the object will also be deleted. See Dependencies. |
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stmtref |
Program line number or statement label to which to transfer control. |
Object identifier.
The NEW( ) function is used in Object Oriented Programming to create a new object based on a specified class name or an existing object (obj_id). If the class name already exists, then its definition is used. If it has not been defined previously, the system attempts to load the program class.pvc and execute/define the DEF CLASS within it (the DEF CLASS clause must be at the start of the program). If the system is unable to properly determine the class definition, an Error #90: Unable to locate Object class definition is generated.
Example:
If the class definition for Customer does not already exist in memory, then the system attempts to load the program Customer.pvc:
Cst=new("Customer")
If this is successful, the NEW( ) function returns the object identifier assigned to the object. The label ON_CREATE is called to initialize the object (if ON_CREATE logic exists in the class definition). Optional parameters can also be used with the NEW( ) function to be passed on to the ON_CREATE entry point:
C=new("Customer",File_number)
In Customer.pvc:
ON_CREATE: \
enter File_no
The OOP interface included in PxPlus allows for the automatic linking of objects to other system components, such as programs, windows, controls, files and other objects. As these other components are closed or deleted, its linked objects will automatically have their usage count decremented. Potentially, the linked objects could also be freed up. This allows programmers to leave much of the housekeeping logic related to objects up to the system as opposed to having to worry about coding for it themselves. By linking objects to items such as the current window, the programmer no longer needs to worry about dropping the object when the window is deleted.
To establish this linkage, the NEW function includes a FOR option where the programmer can specify the component that will be linked to the object:
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Syntax |
Causes the Object to be Deleted When… |
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NEW(..... FOR WINDOW) |
... the current window is destroyed. |
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NEW(..... FOR CONTROL ctlid) |
... the specified control is destroyed. |
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NEW(..... FOR FILE fileno) |
... the specified file is closed. |
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NEW(..... FOR OBJECT [ objid ] ) |
... the current object or object specified is destroyed. |
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NEW(..... FOR PROGRAM) |
... the current program level is exited. |
Where:
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ctlid |
Control identifier that will be linked to the object |
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fileno |
File number that will be linked to the object |
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objid |
Object identifier |
(The object dependency capability for the NEW function was added in PxPlus v6.30.)
Object Oriented Programming
DEF CLASS Define Object Class
REF( ) Control Reference Count