Corrupted data after saving and loading VirtualStringTree

Question

I'm following this tutorial to the letter for saving and loading my VirtualStringTree: http://wiki.freepascal.org/VirtualTreeview_Example_for_Lazarus My problem now is that when I have saved and loaded, my data is corrupted. Chars are changed and added. So does anyone know what the problem is?

You need to read and write more bytes than for that example in Lazarus. To be more specific, you have to `Write(Data.Column, Len * SizeOf(Char));` and `Read(Data.Column, Len * SizeOf(Char));` since strings are 2 bytes per char in your Delphi version. Still, I would leave that example and either make helper functions for string writing and reading, or use a ready made `TBinaryWriter`. — TLama, May 12 '14 at 10:34
You almost have it there. You did give me the info to look for the right code. Tnx — Eszee, May 12 '14 at 11:24

score 2 · Accepted Answer · edited May 23 '17 at 12:27

I found this Link and changed the awnser to fit my code.

Data.Symbol[1]  //Simply points to a char. So I changed it to 'char'

Read:

Stream.Read(Len, SizeOf(Len));
SetLength(Data.Column0, Len);
Stream.Read(PChar(Data.Column0)^, Len * SizeOf(Char));

//Copy/Paste this code for all Columns

Write:

Len := Length(Data.Column0);
Stream.Write(Len, SizeOf(Len));
Stream.Write(PChar(Data.Column0)^, Length(Data.Column0) * SizeOf(Char));

//Copy/Paste this code for all Columns

Second answer by TLama:

Read:

var
  TreeData: PTreeData;
  BinaryReader: TBinaryReader;
begin
  TreeData := Sender.GetNodeData(Node);

  BinaryReader := TBinaryReader.Create(Stream);
  try
    TreeData.Column0 := BinaryReader.ReadString;
    TreeData.Column1 := BinaryReader.ReadString;
    TreeData.Column2 := BinaryReader.ReadString;
  finally
    BinaryReader.Free;
  end;
end;

Write:

var
  TreeData: PTreeData;
  BinaryWriter: TBinaryWriter;
begin
  TreeData := Sender.GetNodeData(Node);

  BinaryWriter := TBinaryWriter.Create(Stream);
  try
    BinaryWriter.Write(TreeData.Column0);
    BinaryWriter.Write(TreeData.Column1);
    BinaryWriter.Write(TreeData.Column2);
  finally
    BinaryWriter.Free;
  end;
end;

I implemented TLama's answer because I really can't be bothered with all the pointers. This code looks much better, is a lot easier to read, takes up less space and does the same.

So to conclude. When you search the web for saving your VST data, your gonna get a lot of junk code. The first answer will fix that code for you. The second will make you smile :)

With binary reader and writer I think you could write something [`like this`](http://pastebin.com/VpyaZ0T6). — TLama, May 12 '14 at 12:03
@TLama That looks good. Much more comprehensive then my code. I'm gonna see if I can implement it. Thank you for that. — Eszee, May 13 '14 at 09:41
@Tlama I Implemented it. If you like I can accept your answer, should you post it ;) Thank you verry much. — Eszee, May 13 '14 at 09:49

Corrupted data after saving and loading VirtualStringTree

1 Answers1