方法指针的RTTI信息

Question

能否获得关于TMethod的RTTI信息？

我可以通过

Instance := TObject(Method.Data);

所以我可以得到实例的RTTI类型，但是如何获得正确的TRttiMethod呢？我想检查使用方法指针传入的方法的属性。

Answer 1

这种方法在理论上是有效的，在实践中有一个很好的改变，但是有几件事情可能会阻止您获得TRttiMethod。

• TMethod记录上写的是Data: Pointer，而不是TObject。这意味着可能会有其他东西，而不是TObject作为Data！这是一个严重的问题，因为如果Data不是TObject，那么尝试从其中提取RTTI将导致运行时错误。
• 并非所有方法都有RTTI。默认情况下，私有区域中的方法没有RTTI，可以使用{$RTTI}停止为公共成员或已发布成员生成RTTI。

这两个问题对于我们在Delphi中通常使用的事件实现类型(双击对象检查器中事件的名称并填写代码)来说不会是一个问题，但我还是认为您不是在谈论"vanila“实现。没有多少人会用属性来装饰默认的事件处理程序！

演示上述所有内容的代码：

program Project15;

{$APPTYPE CONSOLE}

uses
  SysUtils, RTTI;

type
  // Closure/Event type
  TEventType = procedure of object;

  // An object that has a method compatible with the declaration above
  TImplementation = class
  private
    procedure PrivateImplementation;
  public
    procedure HasRtti;

    procedure GetPrivateImpEvent(out Ev:TEventType);
  end;

  TRecord = record
    procedure RecordProc;
  end;

  // an object that has a compatible method but provides no RTTI
  {$RTTI EXPLICIT METHODS([])}
  TNoRttiImplementation = class
  public
    procedure NoRttiAvailable;
  end;

procedure TImplementation.GetPrivateImpEvent(out Ev:TEventType);
begin
  Ev := PrivateImplementation;
end;

procedure TImplementation.HasRtti;
begin
  WriteLn('HasRtti');
end;

procedure TNoRttiImplementation.NoRttiAvailable;
begin
  WriteLn('No RTTI Available');
end;

procedure TRecord.RecordProc;
begin
  WriteLn('This is written from TRecord.RecordProc');
end;

procedure TImplementation.PrivateImplementation;
begin
  WriteLn('PrivateImplementation');
end;

procedure TotalyFakeImplementation(Instance:Pointer);
begin
  WriteLn('Totaly fake implementation, TMethod.Data is nil');
end;

procedure SomethingAboutMethod(X: TEventType);
var Ctx: TRttiContext;
    Typ: TRttiType;
    Method: TRttiMethod;
    Found: Boolean;
begin
  WriteLn('Invoke the method to prove it works:');
  X;
  // Try extract information about the event
  Ctx := TRttiContext.Create;
  try
    Typ := Ctx.GetType(TObject(TMethod(X).Data).ClassType);
    Found := False;
    for Method in Typ.GetMethods do
      if Method.CodeAddress = TMethod(X).Code then
      begin
        // Got the Method!
        WriteLn('Found method: ' + Typ.Name + '.' + Method.Name);
        Found := True;
      end;
    if not Found then
      WriteLn('Method not found.');
  finally Ctx.Free;
  end;
end;

var Ev: TEventType;
    R: TRecord;

begin
  try
    try
      WriteLn('First test, using a method that has RTTI available:');
      SomethingAboutMethod(TImplementation.Create.HasRtti);
      WriteLn;

      WriteLn('Second test, using a method that has NO rtti available:');
      SomethingAboutMethod(TNoRttiImplementation.Create.NoRttiAvailable);
      WriteLn;

      WriteLn('Third test, private method, default settings:');
      TImplementation.Create.GetPrivateImpEvent(Ev);
      SomethingAboutMethod(Ev);
      WriteLn;

      WriteLn('Assign event handler using handler from a record');
      try
        SomethingAboutMethod(R.RecordProc);
      except on E:Exception do WriteLn(E.Message);
      end;
      WriteLn;

      WriteLn('Assign event handler using static procedure');
      try
        TMethod(Ev).Data := nil;
        TMethod(Ev).Code := @TotalyFakeImplementation;
        SomethingAboutMethod(Ev);
      except on E:Exception do WriteLn(E.Message);
      end;
      WriteLn;

    except
      on E: Exception do Writeln(E.ClassName, ': ', E.Message);
    end;
  finally ReadLn;
  end;
end.