Delphi 中的自动释放策略

一、指定 Owner 后, 随 Owner 连带释放:

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//uses Vcl.StdCtrls, Vcl.ExtCtrls;var  panel: TPanel;procedure TForm1.Button1Click(Sender: TObject);begin  panel := TPanel.Create(Self);  panel.Parent := Self;  with TButton.Create(panel) do //AOwner = panel  begin    Parent := panel;    Caption := 'New Button';  end;end;procedure TForm1.Button2Click(Sender: TObject);begin  if Assigned(panel) then    FreeAndNil(panel); //连带释放以它为 Owner 的对象end;

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二、使用接口:

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unit Unit1;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    procedure Button1Click(Sender: TObject);  end;  //  IBass = Interface    function GetName: string;    procedure SetName(const AName: string);    property Name: string read GetName write SetName;  end;  //  TBass = class(TInterfacedObject, IBass)  private    FName: string;  protected    function GetName: string;    procedure SetName(const AName: string);  public    constructor Create(const AName: string);  end;var  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);var  X: IBass;begin  X := TBass.Create('WanYi');  ShowMessage(X.Name);  X.Name := '万一';  ShowMessage(X.Name);  {X 在此自动释放}end;{ TBass }constructor TBass.Create(const AName: string);begin  FName := AName;end;function TBass.GetName: string;begin  Result := FName;end;procedure TBass.SetName(const AName: string);begin  FName := AName;end;end.

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三、使用结构:

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unit Unit1;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    procedure Button1Click(Sender: TObject);  end;  //  TBass = record  private    FName: string;    procedure SetName(const AName: string);  public    constructor Create(const AName: string);    property Name: string read FName write SetName;  end;var  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);var  X: TBass;begin  X := TBass.Create('WanYi');  ShowMessage(X.Name);  X.Name := '万一';  ShowMessage(X.Name);  {X 在此自动释放}end;{ TBass }constructor TBass.Create(const AName: string);begin  FName := AName;end;procedure TBass.SetName(const AName: string);begin  FName := AName;end;end.

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四、在 initialization 中建立、在 finalization 中释放:

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unit Unit1;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    procedure Button1Click(Sender: TObject);  end;var  Form1: TForm1;implementation{$R *.dfm}var  List: TStringList;procedure TForm1.Button1Click(Sender: TObject);begin  List.Clear;  List.Add('WanYi');  ShowMessage(List.Text);end;initialization  List := TStringList.Create;finalization  List.Free;end.

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五、使用动态数组而不是 TList、TStringList 等:

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procedure TForm1.Button1Click(Sender: TObject);var  arr: Array of string;  i: Integer;  s: string;begin  for i := 0 to 6 do  begin    SetLength(arr, Length(arr)+1);    arr[High(arr)] := StringOfChar(Char(i+65), 3);  end;  for s in arr do ShowMessage(s);end;procedure TForm1.Button2Click(Sender: TObject);var  arr: TArray<string>;  i: Integer;  s: string;begin  for i := 0 to 6 do  begin    SetLength(arr, Length(arr)+1);    arr[High(arr)] := StringOfChar(Char(i+65), 3);  end;  for s in arr do ShowMessage(s);end;

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六、使用 TObjectList 而不是 TList:

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uses System.Contnrs;procedure TForm1.Button1Click(Sender: TObject);var  list: TObjectList;  i: Integer;  btn: TButton;begin  list := TObjectList.Create;  for i := 0 to 6 do  begin    btn := TButton.Create(Self);    with btn do begin      Caption := Format('Btn %d', [i+1]);      Parent := Self;      Top := Height * i;      Left := Width * i div 2;    end;    list.Add(btn);  end;  ShowMessage('TObjectList 释放时, 会同时释放其中的对象');  list.Free;end;procedure TForm1.Button2Click(Sender: TObject);var  list: TList;  i: Integer;  btn: TButton;begin  list := TList.Create;  for i := 0 to 6 do  begin    btn := TButton.Create(Self);    with btn do begin      Caption := Format('Btn %d', [i+1]);      Parent := Self;      Top := Height * i;      Left := Width * i div 2;    end;    list.Add(btn);  end;  ShowMessage('TList 释放后, 其中的对象并未释放');  list.Free;end;

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七、使用 TObjectList<T> 而不是 TList<T>:

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uses System.Generics.Collections;procedure TForm1.Button1Click(Sender: TObject);var  list: TObjectList<TButton>;  i: Integer;  btn: TButton;begin  list := TObjectList<TButton>.Create;  for i := 0 to 6 do  begin    btn := TButton.Create(Self);    with btn do begin      Caption := Format('Btn %d', [i+1]);      Parent := Self;      Top := Height * i;      Left := Width * i div 2;    end;    list.Add(btn);  end;  ShowMessage('TObjectList 释放时, 会同时释放其中的对象');  list.Free;end;procedure TForm1.Button2Click(Sender: TObject);var  list: TList<TButton>;  i: Integer;  btn: TButton;begin  list := TList<TButton>.Create;  for i := 0 to 6 do  begin    btn := TButton.Create(Self);    with btn do begin      Caption := Format('Btn %d', [i+1]);      Parent := Self;      Top := Height * i;      Left := Width * i div 2;    end;    list.Add(btn);  end;  ShowMessage('TList 释放后, 其中的对象并未释放');  list.Free;end;

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八、使用结构体而不是结构体指针:

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{假如某个函数的参数需要一个结构指针}function Area(rect: PRect): Integer;begin  Result := rect.Width * rect.Height;//  Result := rect^.Width * rect^.Height;end;{直接声明指针并分配空间后需手动释放}procedure TForm1.Button1Click(Sender: TObject);var  P: PRect;begin  New(P);  P^ := Rect(10, 10, 60, 50);  ShowMessage(IntToStr(Area(P))); //2000  Dispose(P);end;{}procedure TForm1.Button2Click(Sender: TObject);var  R: TRect;begin  R := Rect(10, 10, 60, 50);  ShowMessage(IntToStr(Area(@R))); //2000end;

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