␡
- Defining Properties
- An Example of DefineProperty()
- TddgWaveFile: An Example of DefineBinaryProperty()
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An Example of DefineProperty()
To bring all this rather technical information together, Listing 1 shows the DefProp.pas unit. This unit illustrates the use of DefineProperty() by providing storage for two private data fields: a string and an integer.
Listing 1—DefProp.pas Illustrated Using the DefineProperty() Function
unit DefProp;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;
type
TDefinePropTest = class(TComponent)
private
FString: String;
FInteger: Integer;
procedure ReadStrData(Reader: TReader);
procedure WriteStrData(Writer: TWriter);
procedure ReadIntData(Reader: TReader);
procedure WriteIntData(Writer: TWriter);
protected
procedure DefineProperties(Filer: TFiler); override;
public
constructor Create(AOwner: TComponent); override;
end;
implementation
constructor TDefinePropTest.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
{ Put data in private fields }
FString := 'The following number is the answer...';
FInteger := 42;
end;
procedure TDefinePropTest.DefineProperties(Filer: TFiler);
begin
inherited DefineProperties(Filer);
{ Define new properties and reader/writer methods }
Filer.DefineProperty('StringProp', ReadStrData, WriteStrData,
FString <> '');
Filer.DefineProperty('IntProp', ReadIntData, WriteIntData, True);
end;
procedure TDefinePropTest.ReadStrData(Reader: TReader);
begin
FString := Reader.ReadString;
end;
procedure TDefinePropTest.WriteStrData(Writer: TWriter);
begin
Writer.WriteString(FString);
end;
procedure TDefinePropTest.ReadIntData(Reader: TReader);
begin
FInteger := Reader.ReadInteger;
end;
procedure TDefinePropTest.WriteIntData(Writer: TWriter);
begin
Writer.WriteInteger(FInteger);
end;
end.
CAUTION
Always use the ReadString() and WriteString() methods of TReader and TWriter to read and write string data. Never use the similar-looking ReadStr() and WriteStr() methods because they'll corrupt your DFM file.