Delphi TStringList as object field - delphi

Question

This may very well have been asked many times before but, if so, I cannot for the life of me find the answer. So I apologise in advance if this is the case.
I have this object in a Delphi unit. I'm collating a list of employers from one source which are of type TEmployerData as below.
Once I've collated a list of employers, I will then collect employee and payslips data from other sources which belong to each individual employer.
unit EmployerObjUnit;
interface
uses
Classes, SysUtils, Variants,Types, Generics.Collections, Generics.Defaults, EmployeeObjUnit, PayObjUnit;
type
TEmployerData = class
private
FErID: string;
FErName: string;
FErAccsRef: string;
FErPAYE: string;
FErAddr1: string;
FErAddr2: string;
FErAddr3: string;
FErAddr4: string;
FErPostCd: string;
FErPath: string;
FErEesList: TObjectList<TFPSEmployee>;
FErPayList: TObjectList<TFPSPayment>;
FErYears: TStringList;
procedure SetErID (const Value: string);
procedure SetErName (const Value: string);
procedure SetErAccsRef (const Value: string);
procedure SetErPAYE (const Value: string);
procedure SetErAddr1 (const Value: string);
procedure SetErAddr2 (const Value: string);
procedure SetErAddr3 (const Value: string);
procedure SetErAddr4 (const Value: string);
procedure SetErPostCd (const Value: string);
procedure SetErPath (const Value: string);
constructor Create; overload;
published
property ErID:string read FErID write SetErID;
property ErName:string read FErName write SetErName;
property ErAccsRef:string read FErAccsRef write SetErAccsRef;
property ErPAYE:string read FErPAYE write SetErPAYE;
property ErAddr1:string read FErAddr1 write SetErAddr1;
property ErAddr2:string read FErAddr2 write SetErAddr2;
property ErAddr3:string read FErAddr3 write SetErAddr3;
property ErAddr4:string read FErAddr4 write SetErAddr4;
property ErPostCd:string read FErPostCd write SetErPostCd;
property ErPath: string read FErPath write SetErPath;
property ErEesList: TObjectList<TFPSEmployee> read FErEesList;
property ErPayList: TObjectList<TFPSPayment> read FErPayList;
property ErYears: TStringList read FErYears;
public
procedure AddEmployee(const FPSEmployee: TFPSEmployee);
procedure AddPayslip(const FPSPayslip: TFPSPayment);
procedure AddYear(const Year: string);
end;
All well and dandy so far.
I want to store the employee and payslip data in the ErEEsList and ErPayList ObjectLists, and the relevant years these relate to in the ErYears StringList.
The rest of the class code is:
constructor TEmployerData.Create;
begin
inherited;
FErEesList:=TObjectList<TFPSEmployee>.Create(True);
FErPayList:=TObjectList<TFPSPayment>.Create(True);
FErYears:=TStringList.Create;
end;
procedure TEmployerData.SetErAccsRef(const Value: string);
begin
// all the other setters are in here
end;
procedure TEmployerData.AddEmployee(const FPSEmployee: TFPSEmployee);
var
IsDupe: Boolean;
i: integer;
begin
if FErEesList.Count=0 then
FErEesList.Add(FPSEmployee)
else
begin
IsDupe:=False;
for i := 0 to FErEesList.Count-1 do
begin
if (FErEesList[i].PayID=FPSEmployee.PayID)
AND (FErEesList[i].AccountsRef=FPSEmployee.AccountsRef)
AND (FErEesList[i].TaxYear=FPSEmployee.TaxYear) then
IsDupe:=True;
end;
if IsDupe=False then
FErEesList.Add(FPSEmployee);
if IsDupe=True then
FPSEmployee.Free;
end;
FErEesList.Sort(TComparer<TFPSEmployee>.Construct(
function(const A, B :TFPSEmployee): integer
begin
if A.TaxYear=B.TaxYear then
Result:=0
else if A.TaxYear<B.TaxYear then
Result:=-1
else
Result:=1;
end
));
end;
procedure TEmployerData.AddPayslip(const FPSPayslip: TFPSPayment);
begin
FErPayList.Add(FPSPayslip);
FErPayList.Sort(TComparer<TFPSPayment>.Construct(
function(const A, B :TFPSPayment): integer
begin
if A.TaxYear=B.TaxYear then
Result:=0
else if A.TaxYear<B.TaxYear then
Result:=-1
else
Result:=1;
end
));
end;
procedure TEmployerData.AddYear(const Year: string);
var
i: integer;
GotYr: Boolean;
begin
GotYr:=False;
if FErYears.Count=0 then
FErYears.Add(Year)
else
begin
for i := 0 to FErYears.Count-1 do
begin
if Year=FErYears[i] then
GotYr:=True;
end;
if GotYr=False then
FErYears.Add(Year);
end;
end;
end.
Now, I can collate my list of employers without issue. I can get the information I need for each employee and payslip, BUT when I try to write anything using AddEmployee() or AddYear(), I keep getting Access Violation errors (not even got as far as AddPayslip() yet!). Unfortunately, I'm not fluent enough to figure out why.
The above class is used in one Form unit.
ErsObjList: TObjectList<TEmployerData>;
The above is declared in the Private section of the form unit.
It is created when the form is created. It is freed when the form closes.
Then this is used to fill ErsObjList.
procedure TGetXMLForm.Button1Click(Sender: TObject);
var
//more XML variables
ANode, BNode, CNode: IXMLNode;
NumDir: string;
Employer: TEmployerData;
begin
ErStream:=TFileStream.Create('Employer List.xml', fmOpenRead);
// load of xml setup
try
if Length(XList)>0 then
begin
for i := 0 to Length(XList)-1 do
begin
SetLength(FPSList, 0);
FPSList:=TDirectory.GetFiles(XList[i], 'FPS*.xml', TSearchOption.soAllDirectories);
try
if Length(FPSList)>0 then
begin
// scan through ErListXML for the corresponding number
ErNodes:=ErListXML.DocumentElement.ChildNodes;
if ErNodes.Count>0 then
begin
for x:= 0 to Ernodes.Count-1 do
begin
ANode:=ErNodes[x].ChildNodes.FindNode('Number');
if StrToInt(ANode.Text)=StrToInt(NumDir) then
begin
// create an employer obj from ErListXML
Employer:=TEmployerData.Create;
Employer.ErID:=ANode.Text;
Employer.ErName:=ErNodes[x].ChildNodes.FindNode('Name').Text;
// and so on until
Employer.ErPath:=XList[i];
ErsObjList.Add(Employer);
end;
end;
end;
end;
except
ShowMessage('Exception class name :- '+E.ClassName);
Exit;
end;
end;
end;
ErListXML.Free;
except
ShowMessage('Error reading Employer List xml file');
end;
end;
Button1 gets my employer data from a source, and builds an ObjectList (ErsObjList) without issue.
Then I use this when Button2 is clicked:
procedure TGetXMLForm.Button2Click(Sender: TObject);
var
i: integer;
FPSStream: TStream;
begin
for i := 0 to ErsObjList.Count-1 do
begin
GetPayDetails(ErsObjList[i]);
WriteData;
end;
end;
Which in turn triggers a fuller version of this (I've just removed some basic code for readability - nothing which would affect the issue):
procedure TGetXMLForm.GetRTIDetails(const Employer: TEmployerData);
var
FpsList: TStringDynArray;
// other items
TaxYear: string;
Employee: TFPSEmployee;
Payslip: TFPSPayment;
DateConInf: TFormatSettings;
TaxCd: string;
begin
SetLength(FpsList, 0);
FpsList:=TDirectory.GetFiles(Employer.ErPath, 'FPS*.xml', TSearchOption.soAllDirectories);
if Length(FpsList)>0 then
begin
try
for i := 0 to Length(FpsList)-1 do
begin
// loading some data from XML files
TaxYear:=CNode.ChildNodes.FindNode('RelatedYear').Text;
Employer.AddYear(TaxYear);
// my code then triggers an AV in the "AddYear" procedure
This where it goes wrong.
It does call the procedure AddYear() with the correct value for TaxYear.
It does not flag up any compilation errors.
I would appreciate any help.
edited

Answer 1

For all the code I was trying to cycle through the answer should have been very obvious. But as I said I'm not experienced enough to know.
The TEmployerData class constructor was declared in the wrong place so these
FErEesList: TObjectList<TFPSEmployee>;
FErPayList: TObjectList<TFPSPayment>;
FErYears: TStringList;
were not being initialised correctly when an Employer object was being created. This then caused the runtime AVs.