FPReport Custom elements

FPReport contains support for 4 basic reporting elements:

• Memo
• Shape
• Image
• Checkbox

While these will get you a long way, sometimes something extra is needed.

On this page we explain how to create a new element.

We'll take the sample TReportPolygon as an example.

Create a new element class

Any printable element must descend from TFPReportElement. It must expose published properties which allow the user to control behaviour of the element.

<syntaxhighlighting> TReportPolygon = class(TFPReportElement) Published

 Property Corners : Cardinal Read FCorners Write SetCorners;
 Property LineWidth : Cardinal Read FLineWidth Write SetCLineWidth;
 Property Color : TFPReportColor Read FColor Write FColor;
 // In degrees
 Property RotateAngle : Double Read FRotateAngle Write FRotateAngle;

end; </syntaxhighlighing> The element itself must only know how to read/write its properties from/to a report streamer, and how to copy properties to another instance.

Copying properties to another instance is done in the usual fashion, using the Assign method: <syntaxhighlighting> procedure TReportPolygon.Assign(Source: TPersistent);

Var

 P : TReportPolygon;

begin

 if (Source is TReportPolygon) then
   begin
   P:=Source as TReportPolygon;
   Corners:=P.Corners;
   Color:=P.Color;
   LineWidth:=P.LineWidth;
   RotateAngle:=P.RotateAngle;
   end;
 inherited Assign(Source);

end; </syntaxhighlighting>

Writing properties to the streamer can be done in the WriteElement method, or the DoWriteLocalProperties method: <syntaxhighlighting> procedure TReportPolygon.DoWriteLocalProperties(AWriter: TFPReportStreamer;

 AOriginal: TFPReportElement);

Var

 P : TReportPolygon;

begin

 inherited DoWriteLocalProperties(AWriter, AOriginal);
 if AOriginal is TReportPolygon then
   begin
   P:=AOriginal as TReportPolygon;
   AWriter.WriteIntegerDiff('Color', Color, P.Color);
   AWriter.WriteIntegerDiff('Corners',Corners,P.Color);
   AWriter.WriteIntegerDiff('LineWidth',LineWidth,P.LineWidth);
   AWriter.WriteFloatDiff('RotateAngle',RotateAngle,P.RotateAngle);
   end
 else
   begin
   AWriter.WriteInteger('Color', Color);
   AWriter.WriteInteger('Corners',Corners);
   AWriter.WriteInteger('LineWidth',LineWidth);
   AWriter.WriteFloat('RotateAngle',RotateAngle);
   end;

end; </syntaxhighlighting> The AOriginal is meant do be able to write only properties that differ from the original