我试图找出最好的依赖注入方式,以用于一些需要长时间重构并且必须逐步完成的旧代码。大多数旧类使用“Parent”属性来确定各种事情,并且经常通过构造函数参数传递父属性,如下所示:
constructor TParentObject.Create;
begin
FChildObject := TChildObject.Create(Self);
end;
constructor TChildObject.Create(AParent: TParentObject)
begin
FParent := AParent;
end;
这相当典型于我们的遗留代码库。但是,当移动到接口和构造函数注入时,Spring4D框架在创建Child对象时不知道Parent。因此它将只获取一个新的parent而不是现有的那个。当然,我可以创建一个属性getter/setter,但这将表明类的一个“可选”属性,实际上这是一个必需的属性。请参见下面的代码以获得更多解释:
unit uInterfaces;
interface
uses
Spring.Collections;
type
IChildObject = interface;
IParentObject = interface
['{8EA8F9A2-E627-4546-8008-0A77DA2B16F1}']
function GetSomethingRequiredByChild: string;
procedure SetSomethingRequiredByChild(const Value: string);
property SomethingRequiredByChild: string read GetSomethingRequiredByChild write SetSomethingRequiredByChild;
function GetChild: IChildObject;
property Child: IChildObject read GetChild;
end;
// This introduces a property getter/setter
// However it also implies that Parent can be NIL which it cannot
IChildObject = interface
['{ECCA09A6-4A52-4BE4-A72E-2801160A9086}']
function GetParent: IParentObject;
procedure SetParent(const Value: IParentObject);
property Parent: IParentObject read GetParent write SetParent;
end;
TParentObject = class(TInterfacedObject, IParentObject)
private
FChild: IChildObject;
FSomethingRequiredByChild: string;
function GetChild: IChildObject;
function GetSomethingRequiredByChild: string;
procedure SetSomethingRequiredByChild(const Value: string);
public
constructor Create;
end;
TChildObject = class(TInterfacedObject, IChildObject)
private
FParent: IParentObject;
function GetParent: IParentObject;
procedure SetParent(const Value: IParentObject);
public
// This requries a Parent object, but how does the Spring4D resolve the correct parent?
constructor Create(const AParent: IParentObject);
end;
implementation
uses
Spring.Services;
{ TParentObject }
constructor TParentObject.Create;
begin
// Here is the old way...
FChild := TChildObject.Create(Self); // Old way of doing it
// This is the Service Locator way...
FChild := ServiceLocator.GetService<IChildObject>;
// I would prefer that the Parent is assigned somehow by the Service Locator
// IS THIS POSSIBLE - or am I dreaming?
FChild.Parent := Self;
end;
function TParentObject.GetChild: IChildObject;
begin
Result := FChild;
end;
function TParentObject.GetSomethingRequiredByChild: string;
begin
Result := FSomethingRequiredByChild;
end;
procedure TParentObject.SetSomethingRequiredByChild(const Value: string);
begin
FSomethingRequiredByChild := Value;
end;
{ TChildObject }
constructor TChildObject.Create(const AParent: IParentObject);
begin
FParent := AParent;
end;
function TChildObject.GetParent: IParentObject;
begin
Result := FParent;
end;
procedure TChildObject.SetParent(const Value: IParentObject);
begin
FParent := Value;
end;
end.
也许有一些方法学,可以使用 DI 框架设置父对象,但我不知道该如何操作。
希望我的问题表述清楚了。如果需要,我可以提供更多的描述或代码示例。