Visual Designer cannot load a class which has a private variable as another class which in turn inherits from the initial class

When a class (Class A) has a private variable as a second class (Class B) which in turn inherits from Class A, an error occurs, when opening Class B in the design view.

Jan 9, 2015
Knowledge

Title

URL Name

Visual-Designer-cannot-load-a-class-which-has-a-private-variable-as-another-class-which-in-turn-inherits-from-the-initial-class

Article Number

000149985

Environment

Product: OpenEdge Version: 10.2x, 11.x OS: Windows Other: N/A

Question/Problem Description

When a class (Class A) has a private variable as a second class (Class B) which in turn inherits from Class A, an error occurs, when opening Class B in the design view.

For example:

BaseClass.cls:

CLASS BaseClass INHERITS Progress.Windows.UserControl:
    DEFINE PRIVATE VARIABLE ABaseObject AS SubClass NO-UNDO.
END CLASS.

SubClass.cls:

CLASS SubClass INHERITS BaseClass:
END CLASS.

The same error occurs also when Class A has a private variable defined as itself:

BaseClass.cls:

CLASS BaseClass INHERITS Progress.Windows.UserControl:
    DEFINE PRIVATE VARIABLE ABaseObject AS BaseClass NO-UNDO.
END CLASS.

SubClass.cls:

CLASS SubClass INHERITS BaseClass:
END CLASS.

Steps to Reproduce

Clarifying Information

Error Message

An exception occurred loading the design canvas: The invoked member is not supported before the type is created.

Defect Number

Enhancement Number

Cause

This is expected behaviour.

When the class is created, the session tries to create a proxy object in .NET for this type.
If in the class there is a variable whose type is itself, .NET wouldn’t be able to resolve that because the type doesn’t exist yet. The session is in the processing of building it (i.e., emitting the code for it).

Resolution

Define the member variable as a System.Object.
Then at runtime, cast it to the right type:

BaseClass.cls:

CLASS BaseClass INHERITS Progress.Windows.UserControl: 

    DEFINE VARIABLE oSubClass AS System.Object NO-UNDO. 

    CONSTRUCTOR BaseClass(): 
        CreateSub(). 
    END CONSTRUCTOR. 

    METHOD PROTECTED VOID CreateSub(): 
        oSubClass = NEW SubClass(). 
    END METHOD. 
    
END CLASS.

Workaround

Notes

Keyword Phrase

Last Modified Date

9/12/2024 11:42 PM

Visual Designer cannot load a class which has a private variable as another class which in turn inherits from the initial class

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Visual Designer cannot load a class which has a private variable as another class which in turn inherits from the initial class

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