EvsSimpleGraph (Load / Save Single Graph Objects

[simsee]

Dear all, I'm using TEVSimpleGraph component and I need to load from/save to disk indivual graph objects. Before to devise form scratch a custom solution (i.e. based on approaches described in http://wiki.freepascal.org/Streaming_components), I'm trying to use some built-in methods of above component, but I have some difficulties. Here is my demo code, that produces run-time errors showed in comments... Someone knows this library and can help me? Thanks!

Code: Pascal  [Select][+][-]

1. unit prova;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, usimplegraph, Forms, Controls, Graphics, Dialogs,
9.   StdCtrls;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     Button2: TButton;
18.     EvsSimpleGraph: TEvsSimpleGraph;
19.     procedure Button1Click(Sender: TObject);
20.     procedure Button2Click(Sender: TObject);
21.     procedure FormShow(Sender: TObject);
22.   private
23.     { private declarations }
24.   public
25.     { public declarations }
26.   end;
27.  
28. var
29.   Form1: TForm1;
30.   Rect : TRect;
31.   Node : TEvsGraphNode;
32.   FileStream : TFileStream;
33.  
34. implementation
35.  
36. {$R *.lfm}
37.  
38. { TForm1 }
39.  
40. procedure TForm1.FormShow(Sender: TObject);
41. begin
42.   with Rect do
43.     begin
44.       Left:=100;
45.       Right:=150;
46.       Top:=100;
47.       Bottom:=150;
48.     end;
49.   Node:=EvsSimpleGraph.InsertNode(Rect);
50. end;
51.  
52. procedure TForm1.Button1Click(Sender: TObject); //create rectangle and save it
53. begin
54.   FileStream:=TFileStream.Create('prova',fmCreate or fmOpenWrite);
55.   Node.SaveToStream(FileStream);
56.   FileStream.Free;
57.   EvsSimpleGraph.Clear;   //delete rectangle
58. end;
59.  
60. procedure TForm1.Button2Click(Sender: TObject);  //reload rectangle
61. begin
62.   FileStream:=TFileStream.Create('prova',fmOpenRead);
63.   Node.Create(EvsSimpleGraph);    // External: SIGSEGV  !!!
64.   Node.LoadFromStream(FileStream);  // External: SIGSEGV  !!!
65.   FileStream.Free;
66. end;
67.  
68. end.  

[sky_khan]

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button2Click(Sender: TObject);  //reload rectangle
2. begin
3.   FileStream:=TFileStream.Create('prova',fmOpenRead);
4.   Node.Create(EvsSimpleGraph);    // External: SIGSEGV  !!!
5.   Node.LoadFromStream(FileStream);  // External: SIGSEGV  !!!
6.   FileStream.Free;
7. end;
8.  

You cant do this.
First, it is not how objects are instantiated. You have to use as "Node:=TTheClassYouWant.Create"
Second, if you dont want to stuck with only one kind of shape, you cant create a node from correct class. Because you dont know which kind of object is in stream.

I downloaded and looked EvsSimpleGraph source and I think you can use it's WriteObjects and ReadObjects methods but they are protected.
Still you can crack it like this:

Code: Pascal  [Select][+][-]

1. type
2.   TSimpleGraphCrack = class(TEvsSimpleGraph);  
3.  
4. procedure TForm1.Button2Click(Sender: TObject);
5. var
6.   fs : TFileStream;
7. begin
8.   fs:=TFileStream.Create('prova',fmCreate);
9.   try
10.     if fGraph.SelectedObjects.Count>0 then
11.       TSimpleGraphCrack(fGraph).WriteObjects(fs,fGraph.SelectedObjects);
12.   finally
13.     fs.Free;
14.   end;
15. end;
16.  
17. procedure TForm1.Button3Click(Sender: TObject);
18. var
19.   fs : TFileStream;
20. begin
21.   fGraph.Clear;
22.   fs:=TFileStream.Create('prova',fmOpenRead);
23.   try
24.     if fs.Size>0 then
25.       TSimpleGraphCrack(fGraph).ReadObjects(fs);
26.   finally
27.     fs.Free;
28.   end;
29. end;
30.  

Button2Click will save only selected objects on graph and Button3Click will load what is saved. If you want choose objects by some other way you may create and fill your own list by

myList:=TEvsGraphObjectList.Create;
myList.Add(NodeYouWantToSave);

[simsee]

I madly used the constructor... I apologize... Thanks also for useful suggestions. Only another question: why I can't use LoadFromStream/SaveToStream methods of TEvsGraphNode class to load/save individual objects? According to documentation from the orginal library for Delphi (available with the package at http://www.delphiarea.com/?dl_id=11), these methods are intended to this purpose. Thanks again.

[simsee]

Now it works. Graph objects can be loaded/saved using LoadFromStream/SaveToStream methods, without subclassing TEVSSimpleGraph class. I thought that they did not work because I forgotten to repaint the control with the Invalidate procedure). Here a sample code (I drop expection handlers for sake of brevity):

Code: Pascal  [Select][+][-]

1. unit prova;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, usimplegraph, Forms, Controls, Graphics, Dialogs,
9.   StdCtrls;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     Button1: TButton;
17.     Button2: TButton;
18.     EvsSimpleGraph: TEvsSimpleGraph;
19.     procedure Button1Click(Sender: TObject);
20.     procedure Button2Click(Sender: TObject);
21.     procedure FormShow(Sender: TObject);
22.   private
23.     { private declarations }
24.   public
25.     { public declarations }
26.   end;
27.  
28. var
29.   Form1: TForm1;
30.   Rect : TRect;
31.   Node : TEvsGraphNode;
32.   FileStream : TFileStream;
33.  
34. implementation
35.  
36. {$R *.lfm}
37.  
38. { TForm1 }
39.  
40. procedure TForm1.FormShow(Sender: TObject);  //create a rectangle
41. begin  
42.   with Rect do        
43.     begin
44.       Left:=100;
45.       Right:=150;
46.       Top:=100;
47.       Bottom:=150;
48.     end;
49.   Node:=EvsSimpleGraph.InsertNode(Rect,TEvsRectangularNode);
50. end;
51.  
52. procedure TForm1.Button1Click(Sender: TObject); // save rectangle
53. begin
54.   FileStream:=TFileStream.Create('prova',fmCreate or fmOpenWrite);
55.   Node.SaveToStream(FileStream);
56.   FileStream.Free;
57.   EvsSimpleGraph.Clear;
58. end;
59.  
60. procedure TForm1.Button2Click(Sender: TObject);  //reload rectangle
61. begin
62.   Node:=TEvsRectangularNode.Create(EvsSimpleGraph);
63.   FileStream:=TFileStream.Create('prova',fmOpenRead);
64.   Node.LoadFromStream(FileStream);
65.   FileStream.Free;
66.   EvsSimpleGraph.Invalidate;
67. end;
68.  
69. end.  

[sky_khan]

Well, I assumed you would not want to be stuck with one and only Rectangular shape. If you absolutely know it will be only Rectangular node, not a triangle, not a circle or anything else i guess this will work too.

[simsee]

Thanks again for these additional explanations!