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Prestwood IT Newsletter Nov 2013 Issue - Delphi Edition

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Each month on or after the 1st, and only once a month, we will send you content from up to 5 community groups. If you select this Delphi group, you'll receive the following content below mixed in with the other groups you elect to include.

Prestwood eMag
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  November 2013 - Delphi Edition (762 of 4,804 subscribers receive this group's content.) Year 15 Issue 11  
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Expert guidance from working professionals!
Lighter Side topic:
Scrambled Text
by Mike Prestwood
Apparently if the first and last letters are correct, the rest don't matter.





 Delphi Group Top 
Visit Group | My Group Settings
Using Data topic (classic post):
Delphi Instance Counter
by Mike Prestwood
Implement static member data in Delphi with variables declared in the implementation section (unit scope). Increment and decrement variable in constructor and destructor. Then use a class function to surface the variable's value publicly.

Using Controls topic (classic post):
TDBGrid: Rerarranging Columns at Will
by Wes Peterson

Delphi's TDBGrid is an incredibly useful component; one you'd expect to find in any professional development tool.

One of it's handy behaviors is that users can click in column headers and drag to rearrange column ordering to their liking.

Unfortunately, TDBGrid doesn't offer the developer any really easy way to rearrange grid columns from code. This is inconvenient because you might offer the user a choice of various columns upon which they can search, and it would be nice to make their chosen column the leftmost - at least. Often it makes sense to rearrange other columns as well.

This little class allows you to do that.

It has no exposed methods, and only two properties, so it's incredibly easy to use.

Read on to learn how it works and to get the code.


 Monthly Delphi Lesson
OOP Topic:
Code Snippet of the Month

Delphi for Win32 supports abstract class members using the abstract keyword. You can even instantiate instances of a class that contains abstract members. Then you override each abstract member in a descendant class with Override. Delphi does not support setting an entire class as abstract. You can create an abstract class (a class with one or more abstract methods), but there is no way to tell the compiler to not allow the instantiation of the abstract class. Delphi does not support abstract member properties directly. To implement an abstract properity, make use of abstract methods. That is, you can read a GetPropertyX abstract function and write to a SetPropertyX abstract procedure. In effect, creating  an abstract property.

TCyborg = class(TObject)

public
  procedure Speak(pMessage: String); virtual; abstract;
  procedure Walk; virtual; abstract;
end;
 
TSeries600 = class(TCyborg)

public
  procedure Speak(pMessage: String); override;
  procedure Walk; override;
end;
Delphi for Win32 Topic:
Resource Link of the Month: Delphi for Win32 Roadmap

Official Delphi and C++Builder Roadmap from Codegear.

OOP Topic:
Question: What is the difference between Protected and Strict Protected visibility?

Answer:

Protected visibility means members are invisible outside of the unit. In other words, protected members are visible to the class they are declared in as well as descendant classes and any class declared within the unit.

Strict Protected visibility means that protected members within a class are visible ONLY within the class declared and to descendant classes. In OO terms, this is true protected visibility.

Tool Basics Topic:
Tip of the Month

To insert a GUID into code using the Delphi Editor, use Control + Shift + G.

['{BB45987C-0552-415F-A439-636A87E9F4E2}']

 

However, if you are using either the Visual Studio or Visual Basic key mapping emulation, use Control + Alt + G.



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