Delphi：在运行时查找从给定基类下降的类？ [英] Delphi: At runtime find classes that descend from a given base class?

问题描述

在运行时，是否找到从特定基类下载的所有类？

Is there at way, at runtime, to find all classes that descend from a particular base class?

例如，假装有一个类：

TLocalization = class(TObject)
...
public
   function GetLanguageName: string;
end;

或假装有一个类：

TTestCase = class(TObject)
...
public
   procedure Run; virtual;
end;

或假装有一个类：

TPlugIn = class(TObject)
...
public
   procedure Execute; virtual;
end;

或假装有一个类：

TTheClassImInterestedIn = class(TObject)
...
public
   procedure Something;
end;

在运行时，我想查找从 TTestCase ，以便我可以与他们一起做东西。

At runtime i want to find all classes that descend from TTestCase so that i may do stuff with them.

可以查询RTTI是否有此类信息？

Can the RTTI be queried for such information?

或者：在Delphi中有没有办法走每个课？我可以直接调用：

Alternatively: Is there a way in Delphi to walk every class? i can then simply call:

RunClass: TClass;

if (RunClass is TTestCase) then
begin
   TTestCase(RunClass).Something;
end;

另见

• 查找导出的所有类从python中的给定基类


• Java：在运行时，查找扩展基类的应用程序中的所有类



See also

• Finding all classes that derive from a given base class in python
• Java: At runtime, find all classes in app that extend a base class

推荐答案

嗯，是的，有一种方法，但你不会喜欢它。 （显然，我需要一个这样的免责声明，以防止我的其他完全有帮助的评论被哦，所以知道的，但不是那么宽恕的高级SO成员。）

Well, yes, there is a way, but you're not going to like it. (Appearantly, I need a disclaimer like this, to prevent my otherwise perfectly helpfull comment getting downvoted by the oh-so knowledgable, but not so forgiving 'senior' SO members.)

FYI：以下描述是当Delphi 5是最新版本时，我实际写的一段代码的高级概述。最大的从那时起，该代码被移植到更新的Delphi版本（目前直到Delphi 2010），并且仍然可以工作！

FYI : The following description is a high-level overview of a piece of code I actually wrote when Delphi 5 was the latest & greatest. Since then, that code was ported over to newer Delphi versions (currently up until Delphi 2010) and still works!

对于初学者，你需要知道一个类是什么不仅仅是VMT和附带功能的组合（也可能是某些类型信息，具体取决于编译器版本和设置）。您可能知道，类型为TClass的类只是指向该类VMT的内存地址的指针。换句话说：如果你知道一个类的VMT的地址，那就是TClass指针。

For starters, you need to know that a class is nothing more than a combination of a VMT and the accompanying functions (and maybe some type-info, depending on compiler-version and -settings). As you probably know, a class - as identified by the type TClass - is just a pointer to the memory address of that classes' VMT. In other words : If you known the address of the VMT of a class, that's the TClass pointer as well.

由于这些知识坚定地在你心中，你实际上可以扫描您的可执行内存，并且对于每个地址测试，如果它看起来像一个VMT。似乎是VMT的所有地址都可以添加到列表中，从而完整地概述了可执行文件中包含的所有类。 （实际上，这甚至可以让您访问在单元的实现部分中单独声明的课程，以及作为二进制文件分发的组件和图书馆链接的课程！）

With that piece of knowledge stuck firmly in your mind, you can actually scan your executable memory, and for each address test if it 'looks like' a VMT. All addresses that seem to be a VMT can than be added to a list, resulting in a complete overview of all classes contained in your executable! (Actually, this even gives you access to classes declared solely in the implementation-section of a unit, and classes linked-in from components & libraries that are distributed as binaries!)

当然，有一些地址似乎是一个有效的VMT的风险，但实际上是一些随机的其他数据（或代码） - 但是我已经提出了测试，这从来没有发生过大约6年在十多个积极维护的应用程序中运行此代码）。

Sure, there's a risk that some addresses seem to be a valid VMT, but are actually some random other data (or code) - but with the tests I've come up with, this has never happened to me yet (in about 6 years running this code in more than ten actively maintained applications).

所以这里是你应该做的检查（按照这个确切的顺序！）：

So here's the checks you should do (in this exact order!) :



1. 地址是否等于TObject的地址？如果是这样，这个地址是一个VMT，我们完成了！


2. 读取TClass（address）.ClassInfo;如果它被分配：
   
1. Is the address equal to the address of TObject? If so, this address is a VMT and we're done!
2. Read TClass(address).ClassInfo; If it's assigned :


1. 它应该在代码段内（不，我不会详细介绍 - 只是谷歌）


2. 此ClassInfo的最后一个字节（通过添加SizeOf（TTypeInfo）+ SizeOf（TTypeData）确定））也应该落入该代码段


3. 此ClassInfo类型PTypeInfo）应该有它的种类字段设置为tkClass


4. 在此ClassInfo上调用GetTypeData，导致一个PTypeData
   
1. it should fall inside a code-segment (no, I won't go into details on that - just google it up)
2. the last byte of this ClassInfo (determined by adding SizeOf(TTypeInfo) + SizeOf(TTypeData)) should also fall inside that code-segment
3. this ClassInfo (which is of type PTypeInfo) should have it's Kind field set to tkClass
4. Call GetTypeData on this ClassInfo, resulting in a PTypeData


1. 这也应该是在有效的代码段内


2. 最后一个字节（通过添加SizeOf（TTypeData确定））也应该落入该代码段


3. 此TypeData它的ClassType字段应等于要测试的地址。









• 现在阅读VMT-to-be在偏移量vmtSelfPtr，并测试这是否导致正在测试的地址（应该指向自己）


• 读取vmtClassName并检查它是否指向有效的类名ck指针，再次驻留在有效段中，字符串长度可以接受，IsValidIdent应该返回True）


• 读取vmtParent - 它也应该在有效的代码段


• 现在转换为一个TClass并读取ClassParent - 它也应该属于有效的代码段


• 读取vmtInstanceSize，它应该是> = TObject.InstanceSize和< = MAX_INSTANCE_SIZE（您的确定）


• 从它的ClassParent读取vmtInstanceSize，它也应该是> = TObject.InstanceSize和< =以前读取的实例大小（父类不能大于子类）


• 您可以检查所有来自索引号0及以上的VMT条目是有效的代码指针（尽管确定VMT中的条目数量有一些问题...没有任何指标）。


• 使用ClassParent重新执行这些检查。 （这应该达到上面的TObject测试，或者惨败！）


• Now read the VMT-to-be at the offset vmtSelfPtr and test if this results in the address being tested (should point to itself)
• Read vmtClassName and check if that points to a valid classname (check pointer to reside in a valid segment again, that the string length is acceptable, and IsValidIdent should return True)
• Read vmtParent - it should also fall in a valid code segment
• Now cast to a TClass and read ClassParent - it should also fall in a valid code segment
• Read vmtInstanceSize, it should be >= TObject.InstanceSize and <= MAX_INSTANCE_SIZE (yours to determine)
• Read vmtInstanceSize from it's ClassParent, it should also be >= TObject.InstanceSize and <= the previously read instance size (parent classes can never be larger than child classes)
• Optionally, you could check if all VMT entries from index 0 and upwards are valid code pointers (although it's a bit problematic to determine the number of entries in a VMT... there's no indicator for this).
• Recurse these checks with the ClassParent. (This should reach the TObject test above, or fail miserably!)

如果所有这些检查成立，测试地址是有效的VMT（就我而言），可以添加到列表中。

If all these checks hold, the test-address is a valid VMT (as far as I'm concerned) and can be added to the list.

祝你好运，实现这一切，花了大约一个星期才能得到这个权利。

Good luck implementing this all, it took me about a week to get this right.

请告诉你如何运作。干杯！

Please tell how it works out for you. Cheers!

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