How do I sort a generic list using a custom comparer?

Question

I\'m kinda a Delphi-newbie and I don\'t get how the Sort method of a TList of Records is called in order to sort the records by ascending integer value. I have a record like

Answer 1

I want to share my solution (based on the input I have gathered here).

It's a standard setup. A filedata class that holds data of a single file in a generic TObjectList. The list has the two private attributes fCurrentSortedColumn and fCurrentSortAscending to control the sort order. The AsString-method is the path and filename combined.

function TFileList.SortByColumn(aColumn: TSortByColums): boolean;
var
  Comparison: TComparison;
begin
  result := false;
  Comparison := nil;

  case aColumn of
    sbcUnsorted   : ;
    sbcPathAndName: begin
                      Comparison := function(const Left, Right: TFileData): integer
                                    begin
                                      Result := TComparer.Default.Compare(Left.AsString,Right.AsString);
                                    end;
                    end;
    sbcSize       : begin
                      Comparison := function(const Left, Right: TFileData): integer
                                    begin
                                      Result := TComparer.Default.Compare(Left.Size,Right.Size);
                                      if Result = 0 then
                                        Result := TComparer.Default.Compare(Left.AsString,Right.AsString);
                                    end;
                    end;
    sbcDate       : begin
                      Comparison := function(const Left, Right: TFileData): integer
                                    begin
                                      Result := TComparer.Default.Compare(Left.Date,Right.Date);
                                      if Result = 0 then
                                        Result := TComparer.Default.Compare(Left.AsString,Right.AsString);
                                    end;
                    end;
    sbcState      : begin
                      Comparison := function(const Left, Right: TFileData): integer
                                    begin
                                      Result := TComparer.Default.Compare(Left.FileDataResult,Right.FileDataResult);
                                      if Result = 0 then
                                        Result := TComparer.Default.Compare(Left.AsString,Right.AsString);
                                    end;
                     end;
  end;

  if assigned(Comparison) then
  begin
    Sort(TComparer.Construct(Comparison));

    // Control the sort order
    if fCurrentSortedColumn = aColumn then
      fCurrentSortAscending := not fCurrentSortAscending
    else begin
      fCurrentSortedColumn := aColumn;
      fCurrentSortAscending := true;
    end;

    if not fCurrentSortAscending then
      Reverse;

    result := true;
  end;
end;