Delphi 中的自动释放策略

来自万一老师的博客：http://www.cnblogs.com/del/archive/2011/12/21/2295794.html

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一、指定 Owner 后, 随 Owner 连带释放:

---

//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;

---

二、使用接口:

---

unit Unit1;

interface

uses
  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.

---

三、使用结构:

---

unit Unit1;

interface

uses
  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.

---

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

---

unit Unit1;

interface

uses
  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.

---

五、使用动态数组而不是 TList、TStringList 等:

---

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;

---

六、使用 TObjectList 而不是 TList:

---

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;

---

七、使用 TObjectList<T> 而不是 TList<T>:

---

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;

---

八、使用结构体而不是结构体指针:

---

{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))); //2000
end;