{"id":3948,"date":"2016-06-13T19:19:25","date_gmt":"2016-06-13T11:19:25","guid":{"rendered":"http:\/\/blog.qdac.cc\/?p=3948"},"modified":"2016-06-13T19:19:25","modified_gmt":"2016-06-13T11:19:25","slug":"%e7%bf%bb%e8%af%91-virtual-method-interception-%e8%99%9a%e6%96%b9%e6%b3%95%e6%8b%a6%e6%88%aa","status":"publish","type":"post","link":"https:\/\/blog.qdac.cc\/?p=3948","title":{"rendered":"[\u7ffb\u8bd1] Virtual method interception \u865a\u65b9\u6cd5\u62e6\u622a"},"content":{"rendered":"

\u539f\u6587\u5730\u5740\uff1ahttp:\/\/blog.barrkel.com\/2010\/09\/virtual-method-interception.html<\/a><\/p>\n

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\u6ce8\uff1a\u57fa\u4e8e\u672c\u4eba\u82f1\u6587\u6c34\u5e73\uff0c\u4ee5\u4e0b\u7ffb\u8bd1\u53ea\u662f\u6211\u81ea\u5df1\u7684\u7406\u89e3\uff0c\u5982\u5bf9\u8bfb\u8005\u9020\u6210\u672a\u77e5\u5f71\u54cd\uff0c\u4e00\u5207\u540e\u679c\u81ea\u8d1f\u3002\u6587\u7ae0\u7684\u6392\u7248\u5bf9\u9f50,\u884c\u95f4\u8ddd\u5b9e\u5728\u641e\u5f97\u5934\u5927\uff0c\u51d1\u5408\u770b\u4e00\u4e0b\u3002<\/span><\/p>\n

Delphi XE\u5728rtti.pas\u5355\u5143\u6709\u4e00\u4e2a\u65b0\u7684\u7c7b\u578bTVirtualMethodInterceptor\u3002\u5b83\u6700\u521d\u662f\u8bbe\u8ba1\u7528\u4e8eDataSnap\u7684\u8ba4\u8bc1\u573a\u666f\uff08\u867d\u7136\u6211\u4e0d\u8ba4\u4e3a\u53ea\u80fd\u7528\u5728\u8fd9\u91cc\uff09\u3002<\/p>\n

\u8fd9\u4e2a\u7c7b\u505a\u4e86\u4ec0\u4e48\uff1f\u4ece\u672c\u8d28\u4e0a\u8bb2\uff0c\u5b83\u5728\u8fd0\u884c\u65f6\u52a8\u6001\u5730\u521b\u5efa\u4e86\u4e00\u79cd\u884d\u751fmetaclass\uff0c\u5e76\u91cd\u5199\u7236\u7c7b\u7684\u865a\u65b9\u6cd5\uff0c\u901a\u8fc7\u521b\u5efa\u4e00\u4e2a\u65b0\u7684\u865a\u62df\u65b9\u6cd5\u8868\u548c\u5e76\u586b\u5145\u5230\u7236\u7c7b\u3002\u7528\u6237\u53ef\u4ee5\u62e6\u622a\u865a\u62df\u51fd\u6570\u8c03\u7528\uff0c\u5728\u4ee3\u7801\u5b9e\u73b0\u4e2d\u6539\u53d8\u53c2\u6570\uff0c\u6539\u53d8\u8fd4\u56de\u503c\uff0c\u62e6\u622a\u548c\u4e2d\u65ad\u5f02\u5e38\u6216\u629b\u51fa\u65b0\u7684\u5f02\u5e38\uff0c\u6216\u5b8c\u5168\u53d6\u4ee3\u65b9\u6cd5\u3002\u5728\u6982\u5ff5\u4e0a\uff0c\u5b83\u6709\u70b9\u7c7b\u4f3c\u4e8e.NET\u548cJava\u4e2d\u7684\u52a8\u6001\u4ee3\u7406\u3002\u5b83\u5c31\u50cf\u5728\u8fd0\u884c\u65f6\u4ece\u4e00\u4e2a\u7c7b\u4e2d\u6d3e\u751f\u51fa\u6765\u7684\u65b0\u7c7b\uff0c\u91cd\u5199\u865a\u65b9\u6cd5\uff08\u4f46\u4e0d\u6dfb\u52a0\u65b0\u7684\u5b57\u6bb5\u5c5e\u6027\uff09\uff0c\u7136\u540e\u5c06\u4e00\u4e2a\u5b9e\u4f8b\u7684\u8fd0\u884c\u7c7b\u578b\u66f4\u6539\u4e3a\u8fd9\u4e2a\u65b0\u7684\u6d3e\u751f\u7c7b\u3002<\/p>\n

\u4e3a\u4ec0\u4e48\u8981\u8fd9\u4e48\u505a\uff1f\u4e24\u4e2a\u76ee\u7684\uff1a\u6d4b\u8bd5\u548c\u8fdc\u7a0b\u5904\u7406\u3002(\u201c\u865a\u62df\u65b9\u6cd5\u62e6\u622a\u201d\u6700\u521d\u7528\u5728DataSnap\u8ba4\u8bc1\u90e8\u5206)\u3002<\/p>\n

\u7528\u4e00\u4e2a\u4f8b\u5b50\u5f00\u59cb\uff1a<\/p>\n

uses SysUtils, Rtti; \r\n{$APPTYPE console}\r\n\r\ntype \r\nTFoo = class \r\n\/\/ \u4fee\u6539x \u7684\u503c \r\nfunction Frob(var x: Integer): Integer; virtual; \r\nend;\r\n\r\nfunction TFoo.Frob(var x: Integer): Integer; \r\nbegin \r\nx := x * 2; \r\nResult := x + 10; \r\nend;\r\n\r\nprocedure WorkWithFoo(Foo: TFoo); \r\nvar \r\na, b: Integer; \r\nbegin \r\na := 10; \r\nWriteln(' a = ', a); \r\ntry \r\nb := Foo.Frob(a); \r\nWriteln(' result = ', b); \r\nWriteln(' a = ', a); \r\nexcept \r\non e: Exception do \r\nWriteln(' \u5f02\u5e38: ', e.ClassName); \r\nend; \r\nend;\r\n\r\nprocedure P; \r\nvar \r\nFoo: TFoo; \r\nvmi: TVirtualMethodInterceptor; \r\nbegin \r\nvmi := nil; \r\nFoo := TFoo.Create; \r\ntry \r\nWriteln('\u62e6\u622a\u4ee5\u524d:'); \r\nWorkWithFoo(Foo);\r\n\r\nvmi := TVirtualMethodInterceptor.Create(Foo.ClassType); \r\nvmi.OnBefore := procedure(Instance: TObject; Method: TRttiMethod; \r\nconst Args: TArray<TValue>; out DoInvoke: Boolean; out Result: TValue) \r\nvar \r\ni: Integer; \r\nbegin \r\nWrite('[\u4e4b\u524d] \u8c03\u7528\u65b9\u6cd5', Method.Name, ' \u53c2\u6570: '); \r\nfor i := 0 to Length(Args) - 1 do \r\nWrite(Args[i].ToString, ' '); \r\nWriteln; \r\nend;\r\n\r\n\/\/ \u6539\u53d8 foo \u5b9e\u4f8b\u7684 metaclass pointer \r\nvmi.Proxify(Foo);\r\n\r\n\/\/\u6240\u6709\u7684\u865a\u65b9\u6cd5\u8c03\u7528\u4ee5\u524d\uff0c\u90fd\u8c03\u7528\u4e86OnBefore\u4e8b\u4ef6 \r\nWriteln('\u62e6\u622a\u4ee5\u540e:'); \r\nWorkWithFoo(Foo); \r\nfinally \r\nFoo.Free; \r\nvmi.Free; \r\nend; \r\nend;\r\n\r\nbegin \r\nP; \r\nReadln; \r\nend.<\/pre>\n
\u4ee5\u4e0b\u662f\u8f93\u51fa:<\/p>\n
<\/p>\n
\u4f60\u4f1a\u53d1\u73b0\u5b83\u62e6\u622a\u6240\u6709\u7684\u865a\u62df\u65b9\u6cd5\uff0c\u5305\u62ec\u90a3\u4e9b\u6240\u8c13\u7684\u9500\u6bc1\u8fc7\u7a0b\u4e2d\uff0c\u4e0d\u53ea\u662f\u6211\u4eec\u81ea\u5df1\u58f0\u660e\u7684\u3002<\/p>\n
\uff08\u6790\u6784\u51fd\u6570\u672c\u8eab\u662f\u4e0d\u5305\u62ec\u5728\u5185\u3002\uff09<\/p>\n
\u53ef\u4ee5\u5b8c\u5168\u6539\u53d8\u65b9\u6cd5\u7684\u5b9e\u73b0\uff0c\u5e76\u8df3\u8fc7\u8c03\u7528\u65b9\u6cd5\u7684\u4e3b\u4f53\uff1a<\/strong><\/p>\n
procedure P; \r\nvar \r\nFoo: TFoo; \r\nvmi: TVirtualMethodInterceptor; \r\nctx: TRttiContext; \r\nm: TRttiMethod; \r\nbegin \r\nvmi := nil; \r\nFoo := TFoo.Create; \r\ntry \r\nWriteln('\u62e6\u622a\u4ee5\u524d:'); \r\nWorkWithFoo(Foo);\r\n\r\nvmi := TVirtualMethodInterceptor.Create(Foo.ClassType);\r\n\r\nm := ctx.GetType(TFoo).GetMethod('Frob'); \r\nvmi.OnBefore := procedure(Instance: TObject; Method: TRttiMethod; \r\nconst Args: TArray<TValue>; out DoInvoke: Boolean; out Result: TValue) \r\nbegin \r\nif Method = m then \r\nbegin \r\nDoInvoke := False; \/\/\u539f\u65b9\u6cd5\u7684\u903b\u8f91\u4e0d\u8c03\u7528\u4e86 \r\nResult := 42; \r\nArgs[0] := -Args[0].AsInteger; \r\nend;\r\n\r\nend;<\/pre>\n
\u5728\u8fd9\u91cc\uff0c\u4e2d\u65ad\u4e86\u65b9\u6cd5\u7684\u8c03\u7528\u5e76\u628a\u8fd4\u56de\u7ed3\u679c\u8d4b\u503c\u4e3a42\uff0c\u540c\u65f6\u4fee\u6539\u7b2c\u4e00\u4e2a\u53c2\u6570\u7684\u503c\uff0c\u4ee5\u4e0b\u8f93\u51fa\uff1a<\/p>\n
\u62e6\u622a\u524d:
\nbefore: a = 10
\nResult = 30
\nafter: a = 20
\n\u62e6\u622a\u540e:
\nbefore: a = 10
\nResult = 42
\nafter: a = \u201310<\/p>\n
\u53ef\u4ee5\u901a\u8fc7\u4e00\u4e2a\u5f02\u5e38\u6765\u4e2d\u65ad\u65b9\u6cd5\u7684\u8c03\u7528:<\/strong><\/p>\n
vmi.OnBefore := procedure(Instance: TObject; Method: TRttiMethod;\r\n      const Args: TArray; out DoInvoke: Boolean; out Result: TValue)\r\n    begin\r\n      if Method = m then\r\n        raise Exception.Create('Aborting');\r\n    end;<\/pre>\n
\u8f93\u51fa:<\/p>\n
\u62e6\u622a\u524d:
\nbefore: a = 10
\nResult = 30
\nafter: a = 20
\n\u62e6\u622a\u540e:
\nbefore: a = 10
\nException: Exception<\/p>\n
\u4e0d\u5c40\u9650\u4e8e\u5728\u65b9\u6cd5\u8c03\u7528\u524d\u62e6\u622a\uff0c\u540c\u65f6\u4e5f\u53ef\u4ee5\u5728\u65b9\u6cd5\u8c03\u7528\u540e\u62e6\u622a\uff0c\u5e76\u53ef\u4ee5\u4fee\u6539\u53c2\u6570\u548c\u8fd4\u56de\u503c:<\/strong><\/p>\n
m := ctx.GetType(TFoo).GetMethod('Frob');\r\n    vmi.OnAfter := procedure(Instance: TObject; Method: TRttiMethod;\r\n      const Args: TArray; var Result: TValue)\r\n    begin\r\n      if Method = m then\r\n        Result := Result.AsInteger + 1000000;\r\n    end;<\/pre>\n
\u4ee5\u4e0b\u662f\u8f93\u51fa:<\/p>\n
\u62e6\u622a\u524d:
\nbefore: a = 10
\nResult = 30
\nafter: a = 20
\n\u62e6\u622a\u540e:
\nbefore: a = 10
\nResult = 1000030
\nafter: a = 20<\/p>\n
 <\/p>\n
\u5982\u679c\u865a\u62df\u65b9\u6cd5\u4e2d\u629b\u51fa\u4e86\u4e00\u4e2a\u5f02\u5e38\uff0c\u53ef\u4ee5\u5c4f\u853d\u6389\u8fd9\u4e2a\u5f02\u5e38:<\/strong><\/p>\n
function TFoo.Frob(var x: Integer): Integer;\r\nbegin\r\n  raise Exception.Create('Abort');\r\nend;\r\n\r\n\/\/ ...\r\n    m := ctx.GetType(TFoo).GetMethod('Frob');\r\n    vmi.OnException := procedure(Instance: TObject; Method: TRttiMethod;\r\n      const Args: TArray; out RaiseException: Boolean;\r\n      TheException: Exception; out Result: TValue)\r\n    begin\r\n      if Method = m then\r\n      begin\r\n        RaiseException := False;  \/\/\u5c4f\u853d\u6389\u539f\u65b9\u6cd5\u4e2d\u7684\u5f02\u5e38\r\n        Args[0] := Args[0].AsInteger * 2;\r\n        Result := Args[0].AsInteger + 10;\r\n      end;\r\n    end;<\/pre>\n
\u8f93\u51fa:<\/p>\n
Before hackery:
\nbefore: a = 10
\nException: Exception
\nAfter interception:
\nbefore: a = 10
\nResult = 30
\nafter: a = 20<\/p>\n
\u6709\u4ef6\u4e8b\u8981\u77e5\u9053\uff0c\u7c7bTVirtualMethodInterceptor \u662f\u6ca1\u6709\u7684, \u5b83\u901a\u8fc7\u62e6\u622a\u5bf9\u8c61\u5de5\u4f5c\uff0c\u62e6\u622a\u9700\u8981\u4e00\u4e9b\u5185\u5b58\u5f00\u9500\uff0c\u4f46\u8fd9\u662f\u5f88\u5c11\u7684:<\/p>\n
PPointer(foo)^ := vmi.OriginalClass;<\/p>\n
\u53e6\u4e00\u4e2a\u6307\u9488: \u7c7b\u7684\u7ee7\u627f\u94fe\u662f\u88ab\u6302\u94a9\u8fc7\u7a0b\u6539\u53d8\u4e86\u3002\u8fd9\u53ef\u4ee5\u5f88\u5bb9\u6613\u5730\u663e\u793a:<\/p>\n
\/\/...\r\n    Writeln('After interception:');\r\n    WorkWithFoo(foo);\r\n    \r\n    Writeln('Inheritance chain while intercepted:');\r\n    cls := foo.ClassType;\r\n    while cls <> nil do\r\n    begin\r\n      Writeln(Format('  %s (%p)', [cls.ClassName, Pointer(cls)]));\r\n      cls := cls.ClassParent;\r\n    end;\r\n    \r\n    PPointer(foo)^ := vmi.OriginalClass;\r\n    \r\n    Writeln('After unhooking:');\r\n    WorkWithFoo(foo);\r\n    \r\n    Writeln('Inheritance chain after unhooking:');\r\n    cls := foo.ClassType;\r\n    while cls <> nil do\r\n    begin\r\n      Writeln(Format('  %s (%p)', [cls.ClassName, Pointer(cls)]));\r\n      cls := cls.ClassParent;\r\n    end;\r\n\/\/ ...<\/pre>\n
\u8f93\u51fa:<\/p>\n
Before hackery:
\nbefore: a = 10
\nException: Exception
\nAfter interception:
\nbefore: a = 10
\nResult = 30
\nafter: a = 20
\nInheritance chain while intercepted:
\nTFoo (01F34DA8) \u00a0 \u00a0 \/\/\u8fd0\u884c\u65f6\u589e\u52a0\u7684\u7c7b<\/span>
\nTFoo (0048BD84) \u00a0 \u00a0 \/\/vmi.OriginalClass<\/span>
\nTObject (004014F0)
\nAfter unhooking:
\nbefore: a = 10
\nException: Exception
\nInheritance chain after unhooking:
\nTFoo (0048BD84)
\nTObject (004014F0)<\/p>\n
\u8be5\u529f\u80fd\u4e3b\u8981\u662f\u524d\u671f\u5e93\u7684\u57fa\u7840\u4fee\u8865\uff0c\u4f46\u5e0c\u671b\u4f60\u53ef\u4ee5\u770b\u5230\uff0c\u8fd9\u4e0d\u662f\u592a\u96be\u3002\uff08\u63d0\u4f9b\u4e00\u79cd\u6253\u8865\u4e01\u7684\u65b9\u5f0f\uff09<\/p>\n
\u4e24\u4e2a\u95ee\u9898\uff1a<\/strong><\/p>\n
1\uff1a\u8fd9\u79cd\u65b9\u6cd5\u8ddf\u5199Helper\u7684\u533a\u522b\uff1f<\/p>\n
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\u539f\u6587\u5730\u5740\uff1ahttp:\/\/blog.bar […]<\/p>\n","protected":false},"author":104,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[8],"tags":[],"class_list":["post-3948","post","type-post","status-publish","format-standard","hentry","category-delphi"],"views":2865,"_links":{"self":[{"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/posts\/3948","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/users\/104"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3948"}],"version-history":[{"count":4,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/posts\/3948\/revisions"}],"predecessor-version":[{"id":3952,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=\/wp\/v2\/posts\/3948\/revisions\/3952"}],"wp:attachment":[{"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3948"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3948"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.qdac.cc\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3948"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}