delphi - 命令历史记录单元的意外行为

Question

我编写了这样的模块来存储我的绘图应用程序中图片的最后更改“在Delphi中

    unit HistoryQueue;

    interface

    uses
      Graphics;

   type
myHistory = class
  constructor Create(Size:Integer);
  public
    procedure Push(Bmp:TBitmap);
    function Pop():TBitmap;
    procedure Clean();
    procedure Offset();
    function isEmpty():boolean;
    function isFull():boolean;
    function getLast():TBitmap;
  protected
    historyQueueArray: array of TBitmap;
    historyIndex, hSize:Integer;
  end;

implementation

procedure myHistory.Push(Bmp:TBitmap);
var tbmp:TBitmap;
begin
  if(not isFull) then begin
      Inc(historyIndex);
      historyQueueArray[historyIndex]:=TBitmap.Create;
      historyQueueArray[historyIndex].Assign(bmp);
  end else begin
      Offset();
      historyQueueArray[historyIndex]:=TBitmap.Create;
      historyQueueArray[historyIndex].Assign(bmp);
  end;

end;

procedure myHistory.Clean;
var i:Integer;
begin
{  for i:=0 to hSize do begin
    historyQueueArray[i].Free;
    historyQueueArray[i].Destroy;
  end;        }

end;

constructor myHistory.Create(Size:Integer);
begin
  hSize:=Size;
  SetLength(historyQueueArray, hSize);
  historyIndex:=-1;
end;

function myHistory.isEmpty: boolean;
begin
  Result:=(historyIndex = -1);
end;

function myHistory.isFull: boolean;
begin
  Result:=(historyIndex = hSize);
end;

procedure myHistory.Offset; {to handle overflow}
var i:integer;
begin
  //historyQueueArray[0]:=nil;
  for i:=0 to hSize-1 do begin
    historyQueueArray[i]:=TBitmap.Create;
    historyQueueArray[i].Assign(historyQueueArray[i+1]);
  end;
end;

function myHistory.Pop: TBitmap;
var
  popBmp:TBitmap;
begin
  popBmp:= TBitmap.Create;
  popBmp.Assign(historyQueueArray[historyIndex]);
  Dec(historyIndex);
  Result:=popBmp;
end;

function myHistory.getLast: TBitmap; {this function I use when I need refresh the cnvas when I draw ellipse or rect, to get rid of traces and safe previous changes of the picture}
var
  tBmp:TBitmap;
begin
  tBmp:= TBitmap.Create;
  tBmp.Assign(historyQueueArray[historyIndex]);
  Result:=tBmp;
end;

end.

这就是我使用它的方式

procedure TMainForm.FormCreate(Sender: TObject);
var
  cleanBmp:TBitmap;
begin
    {...}

    doneRedo:=false;

    redomode:=false; undomode:=false;
//init arrays
    picHistory:=myHistory.Create(10);   //FOR UNDO
    tempHistory:=myHistory.Create(10); //FOR REDO

    cleanbmp:=TBitmap.Create;
    cleanbmp.Assign(imgMain.Picture.Bitmap);
    picHistory.Push(cleanbmp);
    cleanbmp.Free;

    {...}

end;

 procedure TMainForm.btnUndoClick(Sender: TObject);
var redBmp:TBitmap;
begin

  undoMode:=true;
  //if there were some changes
  if(not picHistory.isEmpty) then begin
    redBmp:=TBitmap.Create;
    redBmp.Assign(picHistory.getLast);
    //clean canvas
    imgMain.Picture.Bitmap:=nil; 
    //get what was there before
    imgMain.Canvas.Draw(0,0, picHistory.Pop);
    //and in case if we will not make any changes after UNDO(clicked one or more times)
    //and call REDO then
    tempHistory.Push(redBmp);//we save what were on canvas before UNDOand push it to redo history
    redBmp.Free;
  end;

end;


procedure TMainForm.btnRedoClick(Sender: TObject);
var undBmp:TBitmap;
begin
  redoMode:=true;
  if(not tempHistory.isEmpty) then begin

    doneRedo:=True;

    undBmp:=TBitmap.Create;

    undBmp.Assign(tempHistory.getLast);
    imgMain.Picture.Bitmap:=nil;
    MainForm.imgMain.Canvas.Draw(0,0, tempHistory.Pop);

    //same history (like with UNDO implementation) here but reverse
    picHistory.Push(undBmp);
    undBmp.Free;
  end;
end;


{...}

procedure TMainForm.imgMainMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var bmp:TBitmap;
begin
//if mouse were down and then it's up this means we drew something
//and must save changes into history to be able to make UNDO
  {...}
    bmp:=TBitmap.Create;
    try
      bmp.Assign(imgMain.Picture.Bitmap);
      picHistory.Push(bmp);
      //if there are some changes added after redo then we clean redo history
     if (doneRedo) then begin
        tempHistory.Clean;
        doneRedo:=false;
     end;
    finally
      bmp.Free;
      //sor of refresh
      imgMain.Canvas.Draw(0,0, picHistory.getLast);
    end;
  {...}

但问题是它的工作方式与我预期的不同。一个例子:

如果我按一次撤消按钮 - 什么也不会发生。两次 - 它立即完成它应该做的事情。

如果我画了一个椭圆，然后单击“撤消”一次并开始绘制新的椭圆 - 最后绘制的椭圆就消失了!

这是椭圆绘制方法，如果它可以帮助找出问题

    procedure TMainForm.ellipseDraw(X, Y: Integer);
    begin
      imgMain.Canvas.Pen.Color:=useColor;
      imgMain.Canvas.Brush.Color:=scndColor;

      imgMain.Canvas.Pen.Width:=size;

      if(mouseIsDown) then  begin
        imgMain.Canvas.Draw(0,0, picHistory.getLast); //there gonna be no bizzare traces from figures
        imgMain.Canvas.Ellipse(dX, dY, X,Y);
      end;
    end;

Answer 1

回答

If I push undo button once - nothing happens. On twice - it does what it should at once.

这确实正是您的代码所做的:

• 在 imgMainMouseUp 中，将当前图片添加到撤消列表中，并且
• 在 btnUndoClick 中，您可以从撤消列表中检索最后一个位图，该位图与当前在图像上看到的位图相同。

针对这个特定问题的解决方案是将前一个位图添加到撤消列表中，而不是当前位图。

奖金

并发送至地址David's comment关于泄漏，您的实现会泄漏位图，因为:

• 例程Pop和getLast返回一个新本地创建的位图。这将销毁它的责任交给了例程的调用者。您的 MainForm 代码不会破坏这些位图，因此它们是内存泄漏。解决方案是简单地返回数组中的项，而不是创建新的 Bitmap。
• 在 Offset 例程中，您再次创建新的位图并泄漏所有以前的位图。只需将 Queue[I] 分配给 Queue[I + 1]。
• 在 Push 方法中，您忘记释放最后一项。
• 该类没有析构函数，这再次将销毁所有位图的责任交给了对象的用户，需要调用Clean，但事实并非如此。解决方案是向您的对象添加一个析构函数，该析构函数调用 Clean。

除了这些泄漏之外，您的代码还存在更多问题。这里有一些修复和提示:

• 由于动态数组是从零开始的，因此您的 isFull 例程在应该返回 True 时却没有返回 True。它应该实现为 Result := HistoryIndex = hSize - 1;
• 您的数组不是队列 ( FIFO )，而是堆栈 ( LIFO )。
• 您的 Pop 例程不会检查空列表。

总而言之，您的历史课最好看起来像:

uses
  SysUtils, Graphics;

type
  TBitmapHistory = class(TObject)
  private
    FIndex: Integer;
    FStack: array of TBitmap;
    procedure Offset;
  public
    procedure Clear;
    function Count: Integer;
    constructor Create(ACount: Integer);
    destructor Destroy; override;
    function Empty: Boolean;
    function Full: Boolean;
    function Last: TBitmap;
    function Pop: TBitmap;
    procedure Push(ABitmap: TBitmap);
  end;

implementation

{ TBitmapHistory }

procedure TBitmapHistory.Clear;
var
  I: Integer;
begin
  for I := 0 to Count - 1 do
    FreeAndNil(FStack[I]);
  FIndex := -1;
end;

function TBitmapHistory.Count: Integer;
begin
  Result := Length(FStack);
end;

constructor TBitmapHistory.Create(ACount: Integer);
begin
  inherited Create;
  SetLength(FStack, ACount);
  FIndex := -1;
end;

destructor TBitmapHistory.Destroy;
begin
  Clear;
  inherited Destroy;
end;

function TBitmapHistory.Empty: Boolean;
begin
  Result := FIndex = -1;
end;

function TBitmapHistory.Full: Boolean;
begin
  Result := FIndex = Count - 1;
end;

function TBitmapHistory.Last: TBitmap;
begin
  if Empty then
    Result := nil
  else
    Result := FStack[FIndex];
end;

procedure TBitmapHistory.Offset;
begin
  FStack[0].Free;
  Move(FStack[1], FStack[0], (Count - 1) * SizeOf(TBitmap));
end;

function TBitmapHistory.Pop: TBitmap;
begin
  if not Empty then
  begin
    Result := Last;
    Dec(FIndex);
  end;
end;

procedure TBitmapHistory.Push(ABitmap: TBitmap);
begin
  if Full then
    Offset
  else
    Inc(FIndex);
  FStack[Findex].Free;
  FStack[FIndex] := TBitmap.Create;
  FStack[Findex].Assign(ABitmap);
end;

备注:

• 在 Contnrs 单元中还存在一个专门的类 TObjectStack，您可以覆盖/利用它。
• 您的 MainForm 代码也存在问题，但我礼貌地将其留给您解决。