DELPHI FAQ: Использование классовых методов для выявления утечек памяти

Использование классовых методов для выявления утечек памяти

Class Methods aply to the class level, in other words you donґt need an instance to call the method

I wish we could define class objects as well, but they doesnґt exist in Object Pascal, so we will do a trick, we are going to define a variable in the implementation section of the unit, this variable will hold the number of instances the class will have in a moment in time. Object Oriented purist might claim about it, but it works, nobody is perfect (not even Delphi!).

For example say you need to create instances of a class named TFoo, so you create the following Unit.

We will define two class procedures: AddInstance(to increse the counter of instances) and ReleaseInstance(to decrese the number of instances), these are called in the constructor and the destructor acordingly. Finally we define a class function NumOfInstances which returns the actual number of instances.

Add a Initilialization and a Finalization section to the Unit, in the Finalization section ask if the number of instances is <> 0, if this is the case you known that you didinґt destroy all the objects that you created.

unit U_Foo;

interface

uses
  Classes, Windows, SysUtils;

type
  TFoo = class
  private
    class procedure AddInstance;
    class procedure ReleaseInstance;
  public
    constructor Create;
    destructor Destroy; override;
    class function NumOfInstances: Integer;
  end;

implementation

var
  TFoo_Instances: Integer = 0;

  { TFoo }

class procedure TFoo.AddInstance;
begin
  Inc(TFoo_Instances);
end; //end of TFoo.AddInstance

constructor TFoo.Create;
begin
  AddInstance;
end; //end of TFoo.Create

destructor TFoo.Destroy;
begin
  ReleaseInstance;
  inherited;
end; //end of TFoo.Destroy

class function TFoo.NumOfInstances: Integer;
begin
  Result := TFoo_Instances;
end; //end of TFoo.NumOfInstances

class procedure TFoo.ReleaseInstance;
begin
  Dec(TFoo_Instances);
end; //end of TFoo.ReleaseInstance

initialization

finalization

  if TFoo_Instances <> 0 then
    MessageBox(0,
      PChar(Format('%d instances of TFoo active', [TFoo_Instances])),
      'Warning', MB_OK or MB_ICONWARNING);

end.

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