How to read and write “SET OF” type into a file using BinaryWriter?

Question

This is for Delphi Prism.

Say, I have the following enum SET type that I would like to save into a binary file.

Fruit = (Apple, Banana, Mango, Cherry, Grapes, BlueBerry);
Fruits = set of Fruit;

FruitBasket:Fruits;

with Fruit do
  FruitBasket := [Apple, Mango];

BinaryWriter thefile := new BinaryWriter(File.Create("test.dat"));

thefile.write(FruitBasket);   //<<< raises Error - There is no overloaded method "Write" with these parameters 

thefile.Close;

How do you read and write enum SET Type(Fruit) into a binary file using BinaryWriter? I thought I found the answer to my question in another Stackoverflow question but didn't.

I think, I mostly have to loop through its elements, but I needed to know if there is a simpler way to do it.

UPDATE: After the first answer, I tried and came to a quick conclusion, which was a huge mistake on my part. Once I had other issues and errors in my program sorted out, my compiler raised errors on the changes I made as suggested by the first and the one and only answer by CK. I am only able to write but not read it back. Compiler keeps saying - "Type mismatch, cannot assign System.SByte to set of Groups.TFeature"

Code on the top is just a example. Below is the actual code:

Here is the Enum type:

  TFeature = (tfUnit,tfSignal,tfAlarm,tfControl,tfMaker,tfViewer,tfTrend,
              tfComm,tfSystem,tfScan,tfShutdown,tfPID,tfMagiKal);

Here is the SET OF type:

  TFeatures = set of TFeature;

Here are the classes:

  TGroup = class
    name:string;
    rwFeatures:TFeatures;
    roFeatures:TFeatures;
    levels:TLevels;
  private

  public
    constructor;
    Method ReadAGrp(bgreader:BinaryReader);
    Method ReadOld(bgreader:BinaryReader);
    Method WriteAGrp(bgwriter:BinaryWriter);
  end;

  TGroupList = class(ArrayList)
  private

  public
    Method ReadGroups(fname:string);
    Method WriteGroups(fname:string);
    Method AddGroup(group1:TGroup);
    Method DeleteGroup(group1:TGroup);
    Method FindGroup(gname:string):TGroup;
  end;

Here is how I am trying to read and write SET OF type into a binary file using Binarywriter:

procedure TGroup.ReadAGrp(bgreader:BinaryReader);
begin
  name:=bgreader.ReadString;
  rwFeatures := TFeature(bgreader.ReadSByte);
  roFeatures := TFeature(bgreader.ReadSByte);
  levels := TLevels(bgreader.readsbyte);
end;

procedure TGroup.ReadOld(bgreader:BinaryReader);
begin
  name:=bgreader.ReadString;
  rwfeatures := TFeature(bgreader.ReadSByte);
  roFeatures := TFeature(bgreader.ReadSByte);
  levels :=TLevels(bgreader.readsbyte);
end;

procedure TGroup.WriteAGrp(bgwriter:BinaryWriter);
begin
  bgwriter.Write(name);
  bgwriter.Write(rwFeatures.toarray);
  bgwriter.Write(roFeatures.ToArray);
  bgWriter.Write(levels.toarray);
end;

If you could answer with example code or actual code, I would appreciated.

In case you didn't notice, I started a bounty for this question. I really need a working answer. Thanks,

Thanks,

Answer 1

you can serialize it as an array of byte; call .ToArray on your FruitBasket to get it, then use new Fruits(myarrayofbyte) to get it back as a set. Something like:

  var lData := mySet.ToArray();
  bw.Write(lData.Length); // write the length
  bw.Write(lData); // write the bytes

  // Reading:
  var lData := bw.ReadBytes(bw.ReadInt32());
  var newSet := new Fruits(lData);

Answer 2

Based on the example code (FruitBasket), the code as follows.

To write:

thebinarywriter.write(FruitBasket.ToArray);

To Read:

Fruits FruitBasket := new Fruits(thebinaryReader.ReadSByte);

The code has been tested.