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社区首页 >问答首页 >销毁TStringEditLink后的访问冲突(TVirtualStringTree) -拉撒路示例

销毁TStringEditLink后的访问冲突(TVirtualStringTree) -拉撒路示例
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Stack Overflow用户
提问于 2016-08-05 21:49:24
回答 4查看 563关注 0票数 1

我尝试实现了一个基于Lazarius的example的VirtualStringTree编辑器

你能告诉我为什么在TStringEditLink被销毁后我会遇到访问冲突吗?

奇怪的是,只有当我按下ESCAPE或ENTER时才会出现错误。如果我从一个单元格单击到另一个单元格,则没有错误。

就像观察一样,我提出如果从destructor TStringEditLink.Destroy中删除FEdit.Free代码,错误就会消失。

你有解决这个问题的办法吗?

下面是完整的代码:

unit Unit2;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, VirtualTrees, EditorLink, Vcl.StdCtrls,
  Vcl.ExtCtrls, Vcl.Imaging.jpeg;

type
  TTreeData = record
    Fields: array of String;
  end;
  PTreeData = ^TTreeData;

const
  SizeVirtualTree = SizeOf(TTreeData);

type
  TForm2 = class(TForm)
    VirtualTree: TVirtualStringTree;
    procedure FormCreate(Sender: TObject);
    procedure VirtualTreeClick(Sender: TObject);
    procedure VirtualTreeCreateEditor(Sender: TBaseVirtualTree;
      Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
    procedure VirtualTreeEditing(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; var Allowed: Boolean);
    procedure VirtualTreeFreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
    procedure VirtualTreeGetNodeDataSize(Sender: TBaseVirtualTree;
      var NodeDataSize: Integer);
    procedure VirtualTreeGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
    procedure VirtualTreeNewText(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; NewText: string);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.FormCreate(Sender: TObject);
var
  Node: PVirtualNode;
  LTreeData: PTreeData;
begin
  VirtualTree.Clear;
  VirtualTree.BeginUpdate;

  //node 1
  Node:= VirtualTree.AddChild(nil,nil);
  VirtualTree.ValidateNode(Node,False);

  LTreeData:= VirtualTree.GetNodeData(Node);
  SetLength(LTreeData^.Fields,3);

  LTreeData^.Fields[0]:= 'John';
  LTreeData^.Fields[1]:= '2500';
  LTreeData^.Fields[2]:= 'Production';

  //node 2
  Node:= VirtualTree.AddChild(nil,nil);
  VirtualTree.ValidateNode(Node,False);

  LTreeData:= VirtualTree.GetNodeData(Node);
  SetLength(LTreeData^.Fields,3);

  LTreeData^.Fields[0]:= 'Mary';
  LTreeData^.Fields[1]:= '2100';
  LTreeData^.Fields[2]:= 'HR';

  VirtualTree.EndUpdate;
end;

procedure TForm2.VirtualTreeClick(Sender: TObject);
var
  VT: TVirtualStringTree;
  Click: THitInfo;
begin
  VT:= Sender as TVirtualStringTree;
  VT.GetHitTestInfoAt(Mouse.CursorPos.X-VT.ClientOrigin.X, Mouse.CursorPos.Y-VT.ClientOrigin.Y, True, Click);
  VT.EditNode(Click.HitNode,Click.HitColumn);
end;

procedure TForm2.VirtualTreeCreateEditor(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
begin
  EditLink := TStringEditLink.Create;
end;

procedure TForm2.VirtualTreeEditing(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; var Allowed: Boolean);
begin
  Allowed:= True;
end;

procedure TForm2.VirtualTreeFreeNode(Sender: TBaseVirtualTree;
  Node: PVirtualNode);
var
  LTreeData: PTreeData;
begin
  LTreeData:= Sender.GetNodeData(Node);
  Finalize(LTreeData^);
end;

procedure TForm2.VirtualTreeGetNodeDataSize(Sender: TBaseVirtualTree;
  var NodeDataSize: Integer);
begin
  NodeDataSize:= SizeVirtualTree;
end;

procedure TForm2.VirtualTreeGetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: string);
var
  LTreeData: PTreeData;
begin
  if Assigned(Node) and (Column > NoColumn) then
    begin
      LTreeData:= Sender.GetNodeData(Node);
      CellText:= LTreeData^.Fields[Column];
    end;
end;

procedure TForm2.VirtualTreeNewText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; NewText: string);
var
  LTreeData: PTreeData;
begin
  LTreeData:= Sender.GetNodeData(Node);
  LTreeData^.Fields[Column]:= NewText;
end;

end.

EditorLink单元

unit EditorLink;

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs,
  VirtualTrees, Messages, Windows, StdCtrls, Vcl.ExtCtrls;

type

  TStringEditLink = class(TInterfacedObject, IVTEditLink)
  private
    FEdit: TWinControl;
    FTree: TVirtualStringTree;
    FNode: PVirtualNode;
    FColumn: Integer;
    FStopping: Boolean;
  protected
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  public
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

implementation

uses unit2;

destructor TStringEditLink.Destroy;
begin
  FEdit.Free;  //--> seems that due to this I get the access violation
  inherited;
end;

procedure TStringEditLink.EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  case Key of
    VK_ESCAPE:
      begin
        FTree.CancelEditNode;
        Key := 0;
        FTree.setfocus;
      end;
    VK_RETURN:
      begin
       PostMessage(FTree.Handle, WM_KEYDOWN, VK_DOWN, 0);
       Key := 0;
       FTree.EndEditNode;
       FTree.setfocus;
      end;
  end; //case
end;

function TStringEditLink.BeginEdit: Boolean;
begin
  Result := not FStopping;
  if Result then
    begin
      FEdit.Show;
      FEdit.SetFocus;
    end;
end;

function TStringEditLink.CancelEdit: Boolean;
begin
  Result := True;
  FEdit.Hide;
end;

function TStringEditLink.EndEdit: Boolean;
var
  s: String;
begin
  Result := True;
  s := TComboBox(FEdit).Text;
  FTree.Text[FNode, FColumn] := s;

  FTree.InvalidateNode(FNode);
  FEdit.Hide;
  FTree.SetFocus;
end;

function TStringEditLink.GetBounds: TRect;
begin
  Result := FEdit.BoundsRect;
end;

function TStringEditLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
var
  FCellText: String;
  FCellTextBounds: TRect;
  FCellFont: TFont;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;

  FNode := Node;
  FColumn := Column;

  FCellFont:= TFont.Create;
  FTree.GetTextInfo(FNode, FColumn, FCellFont, FCellTextBounds, FCellText);

  FEdit := TComboBox.Create(nil);
  with FEdit as TComboBox do
    begin
      Visible := False;
      Parent := Tree;
      Items.Add('Google');
      Items.Add('Yahoo');
      Items.Add('Altavista');
      OnKeyDown := EditKeyDown;
      Text:= FCellText;
    end;
end;

procedure TStringEditLink.ProcessMessage(var Message: TMessage);
begin
  FEdit.WindowProc(Message);
end;

procedure TStringEditLink.SetBounds(R: TRect);
var
  Dummy: Integer;
begin
  FTree.Header.Columns.GetColumnBounds(FColumn, Dummy, R.Right);
  FEdit.BoundsRect := R;
end;

end.
EN

回答 4

Stack Overflow用户

回答已采纳

发布于 2016-08-26 13:55:24

我在最后使用的解决方案如下所示:

TBasePanel = class(TPanel)
  private
    procedure CMRelease(var Message: TMessage); message CM_RELEASE;
  protected
  public
    procedure Release; virtual;
  end;

TStringEditLink = class(TInterfacedObject, IVTEditLink)
  private
    FBasePanel: TBasePanel;
    ...
  protected
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  public
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

implementation

procedure TBasePanel.CMRelease(var Message: TMessage);
begin
  Free;
end;

procedure TBasePanel.Release;
begin
  if HandleAllocated then
    PostMessage(Handle, CM_RELEASE, 0, 0);
end;

destructor TStringEditLink.Destroy;
begin
  if Assigned(FBasePanel) then FBasePanel.Release;
  inherited;
end;

对于希望同时显示的任意多个组件编辑器,应该将FBasePanel用作ownerparent

票数 0
EN

Stack Overflow用户

发布于 2016-08-06 07:37:17

代码的伪堆栈跟踪说明了这个问题:

FEdit.EditKeyDown()
  -- calls --
FTree.EndEditNode()  { or FTree.CancelEditNode }
  -- which calls --
TStringEditLink.Destroy()
  -- which calls --
FEdit.Free()

在按键事件处理程序代码完成运行之前,FEdit.EditKeyDown()的事件处理程序中的代码将释放FEdit。从而导致访问冲突错误。

我们通过设置一个信号机制来处理这个问题,这样TStringEditLink就可以在完成时向main form发送信号,main form就可以运行代码来销毁TStringEditLink (因为它是最初创建TStringEditLink的那个)。我们向主窗体添加了一个TTimer,并添加了一个接收信号的属性。TTimer监视该属性。TStringEditLink组件有一个指向窗体的指针,因此它可以设置该属性。

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, VirtualTrees;

type
  TEditorAction = (eaCancel, eaAccept, eaNotSet);

  TForm1 = class(TForm)
    vstTree: TVirtualStringTree;
    procedure vstTreeCreateEditor(Sender: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
    procedure DoWatchTreeEditorTimer(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FEndEditTimer: TTimer;
    FEditorAction: TEditorAction;
    procedure SetEditorAction(const Value: TEditorAction);
  public
    property EditorAction: TEditorAction read FEditorAction write SetEditorAction;
  end;

  TPropertyEdit = class(TInterfacedObject, IVTEditLink)
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  private
    FEdit: TWinControl;
    FTree: TVirtualStringTree;
    FNode: PVirtualNode;
    FColumn: Integer;
  public
    FForm: TForm1;
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  FEndEditTimer := TTimer.Create(nil);
  FEndEditTimer.Enabled := False;
  FEndEditTimer.Interval := 100;
  FEndEditTimer.OnTimer := DoWatchTreeEditorTimer;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeAndNil(FEndEditTimer);
end;

procedure TForm1.vstTreeCreateEditor(Sender: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
begin
  EditLink := TPropertyEdit.Create;
  TPropertyEdit(EditLink).FForm := Self; { lets us signal the form when the editor needs to be destroyed }
  FEditorAction := eaNotSet;
end;

procedure TForm1.SetEditorAction(const Value: TEditorAction);
begin
  if FEditorAction <> Value then
  begin
    FEditorAction := Value;
    FEndEditTimer.Enabled := True;
  end;
end;

procedure TForm1.DoWatchTreeEditorTimer(Sender: TObject);
begin
  FEndEditTimer.Enabled := False;
  Application.ProcessMessages;
  case FEditorAction of
    eaCancel:
      begin
        vstTree.CancelEditNode;
        vstTree.SetFocus;
      end;
    eaAccept:
      begin
        vstTree.EndEditNode;
        vstTree.SetFocus;
      end;
  end;
end;

{ TPropertyEdit }

function TPropertyEdit.BeginEdit: Boolean;
begin
  Result := True;
  FEdit.Show;
end;

function TPropertyEdit.CancelEdit: Boolean;
begin
  Result := True;
  FEdit.Hide;
  FForm.FEditorAction := eaCancel;
end;

destructor TPropertyEdit.Destroy;
begin
  if FEdit <> nil then
    FreeAndNil(FEdit);
  inherited;
end;

procedure TPropertyEdit.EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  case Key of
    VK_ESCAPE:
      begin
        Key := Word(0); { some versions of Delphi throw random A/V errors if '0' is not cast as a Word() }
        FForm.EditorAction := eaCancel;
      end;
    VK_RETURN:
      begin
        Key := Word(0); { some versions of Delphi throw random A/V errors if '0' is not cast as a Word() }
        FForm.EditorAction := eaAccept
      end;
  end;
end;

function TPropertyEdit.EndEdit: Boolean;
begin
  Result := True;
  { Do something with the value provided by the user }
  FEdit.Hide;
  FForm.EditorAction := eaAccept;
end;

function TPropertyEdit.GetBounds: TRect;
begin
  Result := FEdit.BoundsRect;
end;

function TPropertyEdit.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;
  FNode := Node;
  FColumn := Column;
  { Setup the editor for user }
  FEdit := TSomeWinControl.Create(nil);
  FEdit.Properties := Values;
  { Capture keystrokes }
  FEdit.OnKeyDown := EditKeyDown;
end;

procedure TPropertyEdit.ProcessMessage(var Message: TMessage);
begin
  FEdit.WindowProc(Message);
end;

procedure TPropertyEdit.SetBounds(R: TRect);
var
  Dummy: Integer;
begin
  FTree.Header.Columns.GetColumnBounds(FColumn, Dummy, R.Right);
  FEdit.BoundsRect := R;
end;

end.

我们的代码做了很多额外的事情,所以上面的代码是基本部分的复制/粘贴,以演示如何克服竞争条件。这是未经测试的,但应该会让你朝着正确的方向前进。

票数 0
EN

Stack Overflow用户

发布于 2016-08-10 18:52:37

一种解决方案也是释放以前创建的控件。

function TStringEditLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
var
  FCellText: String;
  FCellTextBounds: TRect;
  FCellFont: TFont;
  i: Integer;
  Item: TControl;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;

  FNode := Node;
  FColumn := Column;

  FCellFont:= TFont.Create;
  FTree.GetTextInfo(FNode, FColumn, FCellFont, FCellTextBounds, FCellText);

  //----->> free previuous created control <<----------
  for i := (FTree.ControlCount - 1) downto 0 do
    begin
      Item := FTree.controls[i];
      if assigned(item) then
        begin
          if item is TComboBox then FreeAndNil(item);
        end;
    end;
  //---------------------------------------------------

  FEdit := TComboBox.Create(nil);
  with FEdit as TComboBox do
    begin
      Visible := False;
      Parent := Tree;
      Items.Add('Google');
      Items.Add('Yahoo');
      Items.Add('Altavista');
      OnKeyDown := EditKeyDown;
      Text:= FCellText;
    end;
end;
票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/38790920

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