方法指针的RTTI信息 [英] RTTI information for method pointer

问题描述

可以获取关于 TMethod 的RTTI信息吗？

Is it possible to obtain RTTI information about a TMethod?

我可以通过

Instance := TObject(Method.Data);

所以我可以获得实例的RTTI类型，但是如何获得正确的 TRttiMethod ？我想检查使用方法指针传递的方法的属性。

so I can get the RTTI type of the instance, but how can I get the correct TRttiMethod? I want to check for attributes on a method passed in using a method pointer.

推荐答案

这种方法在理论上有效，有一个良好的变化将会在实践中起作用，但有几件事情可能会阻止您持有 TRttiMethod 。

This approach works in theory, and there's a good change it will work in practice, but there are a couple of things that could prevent you from getting hold of the TRttiMethod.

• TMethod 记录说数据：指针，而不是$ code> TObject 。这意味着可能会有另外一个可能的东西 TObject 作为数据！这是一个严重的问题，因为如果 Data 不是 TObject ，那么尝试从中提取RTTI将会导致运行时错误。


• 并非所有方法都具有RTTI。默认情况下，私人区域中的方法没有RTTI，并且可以使用 {$ RTTI} 停止为公共或已发布成员生成RTTI。

• The TMethod record says Data: Pointer, not TObject. This implies there might be a possibility of having something other then an TObject as the Data! This is a serious issue, because if the Data is not TObject, then attempting to extract RTTI from it is going to result in runtime errors.
• Not all methods have RTTI. By default methods in the private area do not have RTTI, and one can use the {$RTTI} to stop generating RTTI for public or published members as well.

这两个问题对于我们在Delphi中的常见类型的事件实现来说不会是一个问题（双击事件在Object中的名称检查员并填写代码），但是再一次，我不认为你在谈论vanila实现。没有多少人使用Attributes来装饰默认的事件处理程序！

Those two issues would not be a problem for the usual type of event implementations we have in Delphi (double-click on the name of the event in Object Inspector and fill in the code), but then again I don't think you're talking about "vanila" implementations. Not many people would decorate the default event handlers with Attributes!

演示所有上述代码：

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.

这篇关于方法指针的RTTI信息的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！