Step 2 - Implement a Property to Specify the Format
Go Up to Creating a Styled FireMonkey Component by Extending an Existing Component
The TClockLabel component created in Step 1 needs to define the date time format when it shows the current time as a property so that component users can specify it.
Contents
Implementing a Property to Specify the Format
To implement the Format property, add the following one line to the published section of TClockLabelclass:
In Delphi:
property Format: String;
In C++:
__property String Format;
Also, add a definition of the constructor to the public section as follows:
In Delphi:
constructor Create(AOwner: TComponent); override;
In C++:
__fastcall TClockLabel(TComponent* Owner);
After Format is changed, Label needs to be updated. To take care of updating the label, introduce the UpdateLabel method as a private member.
The code should look like this:
In Delphi:
type
TClockLabel = class(TLabel)
private
{ Private declarations }
procedure UpdateLabel;
protected
{ Protected declarations }
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
published
{ Published declarations }
property Format: String;
end;
In C++:
//header file
class PACKAGE TClockLabel : public TLabel {
private:
void __fastcall UpdateLabel(void);
protected:
public:
__fastcall TClockLabel(TComponent* Owner);
__published:
__property String Format;
};
After you insert this line, press CTRL+SHIFT+C. The IDE automatically adds a setter for the Format property, and a skeleton for the constructor. The code now should look like this:
In Delphi:
type
TClockLabel = class(TLabel)
private
FFormat: String;
procedure SetFormat(const Value: String);
public
constructor Create(AOwner: TComponent); override;
published
property Format: String read FFormat write SetFormat;
end;
{ TClockLabel }
constructor TClockLabel.Create(AOwner: TComponent);
begin
inherited;
end;
procedure TClockLabel.UpdateLabel;
begin
end;
procedure TClockLabel.SetFormat(const Value: String);
begin
FFormat := Value;
end;
In C++:
//header file
class PACKAGE TClockLabel : public TLabel {
private:
String FFormat;
void __fastcall UpdateLabel(void);
void __fastcall SetFormat(const String Value);
protected:
public:
__fastcall TClockLabel(TComponent* Owner) ;
__published:
__property String Format = {read = FFormat, write = SetFormat};
};
//source file
__fastcall TClockLabel::TClockLabel(TComponent* Owner) : TLabel(Owner) {
}
void __fastcall TClockLabel::UpdateLabel(void) {
}
void __fastcall TClockLabel::SetFormat(const String Value) {
FFormat = Value;
}
According to the documentation for System.SysUtils.DateTimeToString, the typical value for date time format is 'c'. So, initialize the FFormat field with 'c'.
In Delphi
constructor TClockLabel.Create(AOwner: TComponent);
begin
inherited;
FFormat := 'c';
end;
In C++:
//source file
__fastcall TClockLabel::TClockLabel(TComponent* Owner) : TLabel(Owner) {
FFormat = 'c';
}
Now implement the UpdateLabel and SetFormat methods as follows:
In Delphi:
procedure TClockLabel.UpdateLabel;
begin
Text := FormatDateTime(FFormat, Now);
end;
procedure TClockLabel.SetFormat(const Value: String);
begin
FFormat := Value;
UpdateLabel;
end;
In C++:
void __fastcall TClockLabel::UpdateLabel(void) {
Text = FormatDateTime(FFormat, Now());
}
void __fastcall TClockLabel::SetFormat(const String Value) {
FFormat = Value;
UpdateLabel();
}
Inheriting Styles of the Parent Component
If you want your component to inherit styles from the parent component, use the following code:
Delphi:
type
TClockLabel = class(TLabel)
private
{ Private declarations }
procedure UpdateLabel;
function GetDefaultStyleLookupName: string; override;
protected
{ Protected declarations }
public
{ Public declarations }
constructor Create(AOwner: TComponent); override;
published
{ Published declarations }
property Format: String;
end;
function TMyButton.GetDefaultStyleLookupName: string;
begin
Result := Self.GetParentClassStyleLookupName; // stylename of the parent component
end;
C++:
//header file
class PACKAGE TClockLabel : public TLabel {
private:
void __fastcall UpdateLabel(void);
System::UnicodeString __fastcall GetDefaultStyleLookupName(void);
protected:
public:
__fastcall TClockLabel(TComponent* Owner);
__published:
__property String Format;
};
System::UnicodeString __fastcall TClockLabel::GetDefaultStyleLookupName() {
return this->GetParentClassStyleLookupName(); // stylename of the parent component
}