[Solved] Global Variable Not Visible In Another Unit

[Wilko500]

Having read up on variable declaration and making it global I though I had grasped it, but no, I have not. I have read a number of posts with similar issue but have not found solutions so I need a hint as to what I have missed.

I have declared my global variable gChartIndex in the interface section of my main unit FcMain.  That should make it global and visible in other units.

Code: Pascal  [Select][+][-]

1. unit FcMain;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.     Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, ComCtrls,
9.     ExtCtrls, GroupsAndCharts, GetFileVerInfo, Printers,
10.     Drawing, ChartSupport, ClsChartClasses;
11. Var
12.     gChartIndex:  Integer;       //Index of selected chart in ChartListView
13. type
14.  
15.   { TfrmMain }
16.  
17.   TfrmMain = class(TForm)
18.     Button1: TButton;
19.    //Lots of definitions deleted from here from brevity
20.     procedure OptGrpAllClick(Sender: TObject);
21.     procedure OptGrpSelClick(Sender: TObject);
22.  
23.   private
24.  
25.   public
26.  
27.   end;      
28.  

However in my Results unit I reference gChartIndex in procedure TfrmResults.cmdExitClick.  I added FcMain in the Implementation section to avoid a circular reference.  On running the value of gChartIndex is zero.  I also tried to prefix with unit name ie. as FcMain.gChartIndex but still the value is zero.  In both code chunks I have omitted procedures that are not involved to keep  the code as short as possible.  Help please.

Code: Pascal  [Select][+][-]

1. unit Results;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, CheckLst,
9.   ComCtrls, ExtCtrls;
10.  
11. type
12.  
13.   { frmResults }
14.  
15.   { TfrmResults }
16.  
17.   TfrmResults = class(TForm)
18.     cmdPrint: TButton;
19.     cmdExit: TButton;
20.     cmdResPrint: TButton;
21.     cmdResExit: TButton;
22.     Edit1: TEdit;
23.     Edit2: TEdit;
24.     FramePrint: TGroupBox;
25.     GroupBox1: TGroupBox;
26.     Label1: TLabel;
27.     Label2: TLabel;
28.     ListView1: TListView;
29.     ListViewResults: TCheckListBox;
30.     OptPrintAll: TRadioButton;
31.     OptPrintRange: TRadioButton;
32.     OptPrintSel: TRadioButton;
33.     procedure cmdExitClick(Sender: TObject);
34.     procedure FormCreate(Sender: TObject);
35.     procedure ListView1Click(Sender: TObject);
36.   private
37.  
38.   public
39.  
40.   end;
41.  
42. var
43.   frmResults: TfrmResults ;
44.   strVisiblePage:   String;     //The visible page in results list
45.   gResCheck:        Boolean;    //Set when resultls listview checkbox set/unset
46.   gResIndex:        Integer;    //The index of selected item in results ListView
47.  
48. implementation
49.  
50. {$R *.lfm}
51. Uses Drawing, FcMain ;
52. { TfrmResults }
53.  
54. procedure TfrmResults.FormCreate(Sender: TObject);
55. begin
56.  
57. end;
58.  
59. procedure TfrmResults.cmdExitClick(Sender: TObject);
60. begin
61.     //Close open charts
62.     frmMain.GroupBox3.Visible:=True;
63.     frmMain.ListViewCharts.SetFocus;
64.     showMessage(gChartIndex.tostring);
65.     frmMain.ListViewCharts.ItemIndex:=gChartIndex;
66.     frmResults.Close;
67.  
68. end;
69.  

[jamie]

I would say you got your assignment backwards...

[Zath]

unit Results can't see your variable because you don't have unit FcMain declared in the uses clause of unit Results.

[Wilko500]

Its included in the implementation section.  If it's in the interface section I get a circular reference.

[Wilko500]

Sorry, I forgot to include the procedure where gChartIndex is assigned.

Code: Pascal  [Select][+][-]

1. procedure TfrmMain.ListViewChartsClick(Sender: TObject);
2. //ListViewCharts - Select action
3. Var
4.     gChartIndex:      Integer;
5. begin
6. If Assigned(ListViewCharts.Selected) Then  //Prevents access violation if clicking on space
7.     Begin
8.     //Save index of selection
9.     gChartIndex:=ListViewCharts.ItemIndex;
10.     //ShowMessage(index.tostring);
11.     //Get ChartId and GroupId
12.     gChId:=ListViewCharts.Selected.Caption;       //Get selected Chart Id
13.     gGrpId:=ListViewCharts.Selected.SubItems[0];  //Get Selected Group Id
14.     //Now create chart classes
15.     CS:=TChartSettings.Create(gChid);     //Class of Chart Settings
16.     CD:=TChartDetails.Create(gChid);   //Class of Chart Parameters
17.     CG:=TChartGroup.Create(gGrpId);       //Class of Chart Group Details
18.     //Display the chart's settings
19.     LoadChartSettings(gChId);
20.     //And enable the "Select" button
21.     DoButtons(frmMain,'CmdCh', '0001');
22. {EndIf}End;
23. end; /code]

[Wilko500]

Ahhh!  Because it's in implementation it's private to unit Results????? Therefore not defined.

If so how to reference without circular reference?

[egsuh]

Including the unit within uses clause in the implementation setcion is fine, unless you are accessing the variable within interface section. You have re-declared gChartIndex within procedure TfrmMain.ListViewChartsClick(Sender: TObject). In this case, it is regarded as local variable and global variable is not accessed within the procedure.

[MarkMLl]

Including the unit within uses clause in the implementation setcion is fine, unless you are accessing the variable within interface section. You have re-declared gChartIndex within procedure TfrmMain.ListViewChartsClick(Sender: TObject). In this case, it is regarded as local variable and global variable is not accessed within the procedure.

Agreed, provided that the code quoted in two messages is consistent. This isn't FORTRAN where you say that two variables are equivalent, you import the unit (which exports the global variable) and don't redefine.

On the rare occasion it's necessary I find a class helper to be a useful way of avoiding a circular reference:

Code: Pascal  [Select][+][-]

1. unit cms50dpluscode;
2.  
3. interface
4.  
5. type
6.   TCMS50DPlusForm = class(TForm)
7. ...
8.   protected
9.     fcommsThread: TThread;
10. ...
11.   end;
12.  
13. var
14.   CMS50DPlusForm: TCMS50DPlusForm;
15.  
16.  
17. implementation
18. ...
19.  
20. type
21.   TcommsThread= class(TThread)
22. ...
23.   end;
24.  
25.   TCMS50DPlusFormH=                     (* Avoid circular definition            *)
26.     class helper for TCMS50DPlusForm
27.     protected
28.       function CommsThread(): TCommsThread; inline;
29.     end;
30.  
31.  
32. (* This helper avoids problems with circular references, in particular many
33.   occurrences of things like TCommsThread(CMS50DPlusForm.CommsThread).Synchronize()
34.   in favour of the somewhat more concise CMS50DPlusForm.CommsThread.Synchronize().
35. *)
36. function TCMS50DPlusFormH.CommsThread(): TCommsThread; inline;
37.  
38. begin
39.   result := fCommsThread as TcommsThread
40. end { TCMS50DPlusFormH.CommsThread } ;
41.  
42. ...
43.     CMS50DPlusForm.CommsThread.Synchronize(@CMS50DPlusForm.CommsThread.writerPlaybackShim)
44. ...
45.  

However in at least most cases you can achieve the same effect by careful choice of class structure.

MarkMLl

[Wilko500]

Including the unit within uses clause in the implementation setcion is fine, unless you are accessing the variable within interface section. You have re-declared gChartIndex within procedure TfrmMain.ListViewChartsClick(Sender: TObject). In this case, it is regarded as local variable and global variable is not accessed within the procedure.

Thank you.  Problem fixed.  One of those cases when "you can't see the wood for the trees".   Now that you have pointed out the re-declaration I understand why it wasn't working.  The declaration started off in procedure TfrmMain.ListViewChartsClick(Sender: TObject) then got moved BUT I failed to comment it out as I had intended.