问题描述
我有一个包含一些事件属性的类,另一个包含事件处理程序的类。在编译时,我不知道任何一个类的结构,在运行时,我仅使用它们的名称来了解事件属性和事件处理程序之间的匹配。我想使用RTTI将事件处理程序分配给相应的事件属性,该怎么办?
我目前有这样的东西:
type
TMyEvent = reference to procedure(const AInput: TArray<string>; out AOutput: TArray<string>);
TMyBeforeEvent = reference to procedure(const AInput: TArray<string>; out AOutput: TArray<string>; out ACanContinue: boolean);
TMyClass = class
private
FOnBeforeEvent: TMyBeforeEvent;
FOnEvent: TMyEvent;
public
property OnBeforeEvent: TMyBeforeEvent read FOnBeforeEvent write FOnBeforeEvent;
property OnEvent: TMyEvent read FOnEvent write FOnEvent;
end;
TMyEventHandler = class
public
procedure dobeforeEvent(const AInput: TArray<string>; out AOutput: TArray<string>; out ACanContinue: boolean);
procedure DoEvent(const AInput: TArray<string>; out AOutput: TArray<string>);
end;
procedure AssignEvent;
implementation
uses
Vcl.Dialogs,System.RTTI;
{ TMyEventHandler }
procedure TMyEventHandler.dobeforeEvent(const AInput: TArray<string>;
out AOutput: TArray<string>; out ACanContinue: boolean);
begin
// do something...
end;
procedure TMyEventHandler.DoEvent(const AInput: TArray<string>;
out AOutput: TArray<string>);
begin
// do something...
end;
procedure AssignEvent;
var
LObj: TMyClass;
LEventHandlerObj: TMyEventHandler;
LContextObj,LContextHandler: TRttiContext;
LTypeObj,LTypeHandler: TRttiType;
LEventProp: TRttiProperty;
LMethod: TRttiMethod;
LNewEvent: TValue;
begin
LObj := TMyClass.Create;
LEventHandlerObj := TMyEventHandler.Create;
LContextObj := TRttiContext.Create;
LTypeObj := LContextObj.GetType(LObj.Classtype);
LEventProp := LTypeObj.GetProperty('OnBeforeEvent');
LContextHandler := TRttiContext.Create;
LTypeHandler := LContextHandler.GetType(LEventHandlerObj.Classtype);
LMethod := LTypeHandler.getmethod('dobeforeEvent');
LEventProp.SetValue(LObj,LNewEvent {--> what value should LNewEvent have?});
end;
解决方法
reference to procedure(...)
是匿名方法类型。在幕后,它通过与IInterface
的参数匹配的Invoke()
方法实现为接口对象(即实现procedure
接口的类)。
例如,由于TMyEventHandler.DoBeforeEvent()
与该条件不匹配,因此不能将TMyClass.OnBeforeEvent
直接与TMyEventHandler
一起使用。但是,您可以将对DoBeforeEvent()
的调用包装在实际的匿名过程中,例如:
procedure AssignEvent;
var
LObj: TMyClass;
LEventHandlerObj: TMyEventHandler;
LEventHandler: TMyBeforeEvent;
LContextObj: TRttiContext;
LMethod: TRttiMethod;
LEventProp: TRttiProperty;
begin
LObj := TMyClass.Create;
LEventHandlerObj := TMyEventHandler.Create;
LContextObj := TRttiContext.Create;
LMethod := LContextObj.GetType(LEventHandlerObj.ClassType).GetMethod('DoBeforeEvent');
LEventHandler := procedure(const AInput: TArray<string>; out AOutput: TArray<string>; out ACanContinue: boolean);
begin
// Note: I don't know if/how TRttiMethod.Invoke() can handle
// 'out' parameters,so this MAY require further tweaking...
LMethod.Invoke(LEventHandlerObj,[AInput,AOutput,ACanContinue]);
end;
LEventProp := LContextObj.GetType(LObj.ClassType).GetProperty('OnBeforeEvent');
LEventProp.SetValue(LObj,TValue.From(LEventHandler));
end;
与将TMyEventHandler.DoEvent()
与TMyClass.OnEvent
一起使用。
或者,如果将reference to procedure(...)
更改为procedure(...) of object
,则可以使用TMethod
记录将TMyEventHandler.DoBeforeEvent()
直接分配给{ {1}},例如:
TMyClass.OnBeforeEvent
与将procedure AssignEvent;
var
LObj: TMyClass;
LEventHandlerObj: TMyEventHandler;
LEventHandler: TMyBeforeEvent;
LContextObj: TRttiContext;
LEventProp: TRttiProperty;
LMethod: TRttiMethod;
begin
LObj := TMyClass.Create;
LEventHandlerObj := TMyEventHandler.Create;
LContextObj := TRttiContext.Create;
LEventProp := LContextObj.GetType(LObj.ClassType).GetProperty('OnBeforeEvent');
LMethod := LContextObj.GetType(LEventHandlerObj.ClassType).GetMethod('DoBeforeEvent');
with TMethod(LEventHandler) do
begin
Code := LMethod.CodeAddress;
Data := LEventHandlerObj;
end;
LEventProp.SetValue(LObj,TValue.From(LEventHandler));
end;
与TMyEventHandler.DoEvent()
一起使用。
好问题!
我相信我找到了一种合理的方法。
为说明起见,请创建一个新的VCL应用程序,该应用程序具有一个窗体(Form1
)和一个按钮(Button1
)。给表单一个OnClick
处理程序:
procedure TForm1.FormClick(Sender: TObject);
begin
ShowMessage(Self.Caption);
end;
我们将尝试仅使用RTTI以及属性和方法名称(作为字符串)将此处理程序分配给按钮的OnClick
属性。
要记住的关键是方法指针是一对(代码指针,对象指针),特别是TMethod
记录:
procedure TForm1.FormCreate(Sender: TObject);
var
C: TRttiContext;
b,f: TRttiType;
m: TRttiMethod;
bp: TRttiProperty;
handler: TMethod;
begin
C := TRttiContext.Create;
f := C.GetType(TForm1);
m := f.GetMethod('FormClick');
b := C.GetType(TButton);
bp := b.GetProperty('OnClick');
handler.Code := m.CodeAddress;
handler.Data := Form1;
bp.SetValue(Button1,TValue.From<TNotifyEvent>(TNotifyEvent(handler)));
end;