Sorting a memo in Delphi

Question

I have to make an highscore memo for my school in Delphi 6. Is there a way to sort the MemoLines on numbers or alphabet?

I use 4 Tedits and 1 TMemo. If the game ends, my code will check who has got the highest score. This is how to check if Player1 got a higher score then player2:

if in1>p2in1 then begin
  highscore.naammemo.Lines.Add(Speler1.Caption);
  highscore.saldomemo.Lines.Add(Saldo1.Text);
end;

How do I create a code for the TMemo to sort the highest score of each game?

Answer 1

Here's some sample code that will let you experiment with sorting. It uses a text value and a number on each line, separated by a tab character (#9). There's code at the start of each button click handler that resets the text to the same starting value, so you can see the effects. The first button (btnNameSort) sorts by the text values using the standard TStringList.Sort, and the second (btnScoreSort) sorts by the numeric value using a TListSortCompare custom sort function.

// Simply uses TStringList.Sort to sort in the default (alpha) order
procedure TForm1.btnNameSortClick(Sender: TObject);
var
  SL: TStringList;
begin
  InitMemoLines;
  SL := TStringList.Create;
  try
    Memo1.Lines.BeginUpdate;
    try
      SL.Assign(Memo1.Lines);
      SL.Sort;
      Memo1.Lines.Assign(SL);
    finally
      Memo1.Lines.EndUpdate;
    end;
  finally
    SL.Free;
  end;
end;

// Sorts by extracting the text after the tab character on the lines
// being compared, converting to numbers, and comparing the numbers.
// Called by using SL.CustomSort in the btnScoreSortClick event
// below.
//
// NOTE: Will obviously fail if the lines don't contain a tab, or
// if the content after the tab can't be converted to a numeric.
// Neither of those cases is handled here for brevity. 
function NumberedListSort(List: TStringList; Index1, Index2: Integer): Integer;
var
  Line1, Line2: string;
  Num1, Num2: Integer;
begin
  Line1 := List[Index1];
  Line2 := List[Index2];
  Num1 := StrToInt(Copy(Line1, Pos(#9, Line1) + 1, 255));
  Num2 := StrToInt(Copy(Line2, Pos(#9, Line2) + 1, 255));
  Result := Num1 - Num2;
end;

// Calls NumberedListSort to sort by the numbers on the right end 
// of each line in the memo
procedure TForm1.btnScoreSortClick(Sender: TObject);
var
  SL: TStringList;
begin
  InitMemoLines;
  SL := TStringList.Create;
  try
    Memo1.Lines.BeginUpdate;
    try
      SL.Assign(Memo1.Lines);
      SL.CustomSort(NumberedListSort);
      Memo1.Lines.Assign(SL);
    finally
      Memo1.Lines.EndUpdate;
    end;
  finally
    SL.Free;
  end;
end;

// Calls InitMemoLines to set the starting content of the memo
procedure TForm1.FormCreate(Sender: TObject);
begin
  InitMemoLines;
end;

// Generates content of memo
procedure TForm1.InitMemoLines;
var
  i: Integer;
begin
  Memo1.Lines.Clear;
  for i := 1 to 10 do
    Memo1.Lines.Append(Format('Line ' + Chr(90 - i) + #9 + ' %d', [i]));
end;

Answer 2

I think the simplest way would be something along these lines:

1. Transfer the content from the memo to a TStringList instance.
2. Call CustomSort on the TStringList instance, passing an appropriate sort compare function.
3. Transfer the content back to the memo.

Steps 1 and 3 are simple calls to Assign. So step 1 would be:

StringList.Assign(Memo.Lines);

And step 3 would be:

Memo.Lines.Assign(StringList);

Step 2 is the tricky bit. You've got to provide a compare function of this type:

TStringListSortCompare = function(List: TStringList; 
  Index1, Index2: Integer): Integer;

Your function will look like this:

function MySortCompare(List: TStringList; Index1, Index2: Integer): Integer;
begin
  Result := MyCompareStrings(List[Index1], List[Index2]);
end;

where MyCompareStrings is a function that compares two strings according to your rules. The return value of that function follows the usual convention for a compare function. Negative means less than, positive means greater than and zero means equal.

Of course, you can write the logic directly inline to MySortCompare if you prefer.