Step 2 - Implement a Property to Specify the Number of Sides
Go Up to Creating a FireMonkey Primitive Control
The TRegularPolygon component needs to define the number of sides as a property so that component users can specify it. To implement a property (named NumbersOfSides), add the following line to the published section of the TRegularPolygon class:
property NumberOfSides: Integer;
Also, add a definition of the constructor to the public section as follows:
constructor Create(AOwner: TComponent); override;
So the code should look like this:
type
TRegularPolygon = class(TShape)
private
{ Private declarations }
protected
{ Protected declarations }
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
published
{ Published declarations }
property NumberOfSides: Integer;
end;
After you insert these lines, press CTRL+SHIFT+C. The IDE automatically adds the setter for the NumberOfSides property, and a skeleton for the constructor. The code now should look like this:
TRegularPolygon = class(TShape)
private
FNumberOfSides: Integer;
procedure SetNumberOfSides(const Value: Integer);
{ Private declarations }
protected
{ Protected declarations }
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
published
{ Published declarations }
property NumberOfSides: Integer read FNumberOfSides write SetNumberOfSides;
end;
constructor TRegularPolygon.Create(AOwner: TComponent);
begin
inherited;
end;
procedure TRegularPolygon.SetNumberOfSides(const Value: Integer);
begin
FNumberOfSides := Value;
end;
As with every polygon, the number of sides should be at least 3. So change the implementation of the SetNumberOfSides method as follows:
procedure TRegularPolygon.SetNumberOfSides(const Value: Integer);
begin
if (FNumberOfSides <> Value) and (Value >= 3) then
begin
FNumberOfSides := Value;
Repaint;
end;
end;
The Repaint method tells the FireMonkey framework that this component needs to be repainted when the number of sides changes. In the constructor, you need to initialize the value of FNumbersOfSides field to make it a minimum of 3. By changing the field (instead of a property) you avoid unnecessary calls to the repaint method. Add the following code to the constructor:
constructor TRegularPolygon.Create(AOwner: TComponent);
begin
inherited;
FNumberOfSides := 3;
end;