How can I save and load my svTree data structure? - delphi

Question

I am trying to implement a simple contact manager using the VirtualStringTree component. I have it set up to look like a list-view component with only three columns that will all contain text:
For the data structure, I am using svTree by Linas, which was mentioned in another Stack Overflow question.
I have declared a record like this:
type
TMainData = record
Name, Email, Password: string;
end;
In the form's OnCreate I have this:
procedure TForm1.FormCreate(Sender: TObject);
begin
MyTree := TSVTree<TMainData>.Create(False);
MyTree.VirtualTree := vst1;
end;
I am adding the data from TEdits like this:
procedure TForm1.BuildStructure;
var
svNode: TSVTreeNode<TMainData>;
Data: TMainData;
begin
MyTree.BeginUpdate;
try
Data.Name := edtname.Text;
Data.Email := edtEmail.Text;
Data.Password := edtPassword.Text;
svNode := MyTree.AddChild(nil, Data);
finally
MyTree.EndUpdate;
end;
Label1.Caption := 'Count: '+IntToStr(MyTree.TotalCount);
end;
How can I save this into a stream or a file to be loaded back? I have tried using MyTree.SaveToFile('C:/Test.dat') and MyTree.LoadFromFile('C:/Test.dat'), but when it's loaded back the tree view contains no data, only a blank row.

Answer 1

You need to set OnLoadNode and OnSaveNode procedures for your TSVTree and implement your logic here. You can look at Project2 in the Demos folder. E.g.:
uses
uSvHelpers;
MyTree.OnSaveNode := DoSave;
MyTree.OnLoadNode := DoLoad;
procedure TForm1.DoLoad(Sender: TSVTree<TMainData>; Node: TSVTreeNode<TMainData>; Stream: TStream);
var
obj: TMainData;
begin
//
if Assigned(Node) then
begin
//read from stream
//read in correct order
obj.Name := Stream.AsString;
obj.Email := Stream.AsString;
obj.Password := Stream.AsString;
Node.FValue := obj;
end;
end;
procedure TForm1.DoSave(Sender: TSVTree<TMainData>; Node: TSVTreeNode<TMainData>; Stream: TStream);
begin
if Assigned(Node) then
begin
//read from stream
Stream.WriteString(Node.FValue.Name);
Stream.WriteString(Node.FValue.Email);
Stream.WriteString(Node.FValue.Password);
end;
end;
After that you can just call MyTree.SaveToFile('C:/Test.dat') or MyTree.LoadFromFile('C:/Test.dat'). In my demo and this example i've used another unit (uSvHelpers) which implements TStream helper for more OO stream support. You can of course use your own way to write your data information to stream.

Answer 2

Looks like you need to implement the OnSaveNode and OnLoadNode events:
procedure TForm.VTLoadNode(Sender: TBaseVirtualTree;
Node: PVirtualNode; Stream: TStream);
begin
// Load Node Data record from the stream
end;
procedure TForm.VTSaveNode(Sender: TBaseVirtualTree;
Node: PVirtualNode; Stream: TStream);
begin
// Save Node Data record to the stream
end;