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Tip of the Day
Language: Pascal
Expertise: Beginner
Feb 25, 1999

WEBINAR:

On-Demand

Application Security Testing: An Integral Part of DevOps


Delphi MDI Form

Question:
Imagine an MDI application where the MDIFrame has many MDIChild forms—each one derived from TBlueForm class. The TBlueForm class has a public method named ChangeColor which only makes the form's color change from gray to blue. How do I call the ChangeColor method from the MDIFrame without referencing the Childform's name but using the ActiveMDIChild property of the MDIFrame?
          ActiveMDIChild.ChangeColor;
When I tried this, the compiler returned the error:
          Undeclared identifier:'ChangeColor'
So it seems that ActiveMDIChild only recognizes the methods inherited of TForm. All the MDIChild forms were included in the uses session of the MDIFrame.

Answer:
You could try typecasting the ActiveMDIChild like so:

TBlueForm(ActiveMDIChild).ChangeColor;
This code should work.
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