使用IMetadataImport时如何获取枚举值 [英] How to get an enumeration value when using IMetadataImport

问题描述

使用 IMetadataImport 时，如何从*.winmd文件中获取与枚举关联的数值?

How to you get the numeric value associated with an enum from a *.winmd file when using IMetadataImport?

一个很好的例子是 ApplicationHighContrastAdjustment 枚举:

A good example is ApplicationHighContrastAdjustment enumeration:

//Windows.UI.Xaml.ApplicationContrastMode (@020000006)
public enum ApplicationHighContrastAdjustment : uint
{
    None = 0u,
    Auto = 4294967295u
}

大多数枚举是0, 1, 2, ....但这枚举成员上还指定了其他值:

Most enumerations are 0, 1, 2, .... But this one has other values specified on the enum members:

• 0
• 4294967295

如何阅读以获取那些 UInt32 值

注意:该问题不必仅适用于WinRT. C#世界中使用相同的接口来检查.NET托管程序集. WinRT恰好使用相同的汇编文件格式.

Note: The question doesn't have to apply to just WinRT. The same interfaces are used in the C# world to inspect .NET managed assemblies. WinRT happens to use the same assembly file format.

我正在使用IMetadataImport来读取*.winmd(用于WinRT应用程序的TLB的现代版本)的内容.但是这个问题同样适用于读取有关.NET托管程序集的元数据.

I'm using IMetadataImport to read the contents of an *.winmd (the modern version of TLBs for WinRT applications). But the question applies equally to reading metadata about a .NET managed assembly.

关于如何启动并运行读取winmd元数据文件的精简版:

The abridged version of how to get up and running reading winmd metadata file:

// Create your metadata dispenser:
IMetadataDispsener dispener;
MetaDataGetDispenser(CLSID_CorMetaDataDispenser, IMetaDataDispenser, out dispenser);

//Open the winmd file we want to dump
String filename = "C:\Windows\System32\WinMetadata\Windows.UI.Xaml.winmd";

IMetaDataImport reader; //IMetadataImport2 supports generics
dispenser.OpenScope(filename, ofRead, IMetaDataImport, out reader); //"Import" is used to read metadata. "Emit" is used to write metadata.

获取有关枚举的信息(自动，无)

我们现在有一个读者.除了枚举程序集中的类型外，我还可以直接跳到这个问题的有趣的地方:0x02000006:

//Get metadata for enum Windows.UI.Xaml.ApplicationHighContrastAdjustment
mdToken tokenID = 0x02000006; //Windows.UI.Xaml.ApplicationHighContrastAdjustment

//btw, this is all hypothetical code that is vaguely C#/Java-like.

Pointer enum = null;
mdToken memberID;
int nCount;
while (reader.EnumMembers(ref enum, tokenID, out memberID, 1, out nCount) == S_OK)
{
   //out MemberID receives the TokenID of each member of the enumeration
}
reader.CloseEnum(enum);

对EnumMembers的调用返回了枚举的三个成员:

The call to EnumMembers returns us the three members of the enumeration:

• Windows.UI.Xaml.ApplicationContrastMode (@ 02000006)
  • 值__ (@ 04000439，私有)
  • 没有(@ 0400043A，公开)
  • 自动(@ 0400043B，公开)
  • Windows.UI.Xaml.ApplicationContrastMode (@02000006)
    • value__ (@04000439, private)
    • None (@0400043A, public)
    • Auto (@0400043B, public)

    我们实际上是通过调用 GetMemberProps 来找出他们的名字的(而且这个名字是私人的):

    We actually find out their names (and that fact that one is private) through a call to GetMemberProps:

    IMetaDataImporter.GetMemberProps(0x0400043A, ...); //"None"
    IMetaDataImporter.GetMemberProps(0x0400043B, ...); //"Auto"  
    

    注意:GetMemberProps是一个辅助函数.来自微软:

    Note: GetMemberProps is a helper function. From Microsoft:

    这是一个简单的辅助方法:如果 md 是MethodDef，则我们调用 GetMethodProps ；如果 md 是FieldDef，则称为 GetFieldProps .有关详细信息，请参见这些其他方法.

    This is a simple helper method: if md is a MethodDef, then we call GetMethodProps; if md is a FieldDef, then we call GetFieldProps. See these other methods for details.

    GetMemberProps 方法返回有关每个枚举值的全部信息-但不返回其实际枚举 value :

    The GetMemberProps method returns a whole host of information about each enum value - but not their actual enum value:

    | Metadata          | @0400043A         | @0400043B       |
    |-------------------|-------------------|-----------------|
    | Name              | "None"            | "Auto"          |
    | Attributes        | 0x00008056        | 0x00008056      |
    | Signature         | 06 11 A3 95       | 06 11 A3 95     |
    | CodeRVA           | 0x00000000        | 0x00000000      |
    | CPlusTypeFlag     | ELEMENT_TYPE_U4   | ELEMENT_TYPE_U4 |
    | DefaultValue      | (none)            | (none)          |
    

    我在成员属性中找不到任何指示该枚举分配值的内容.并查看其他 IMetadataImporter 方法:

    I cannot find anything in the member properties that indicates the enumeration's assigned value. And looking at other IMetadataImporter methods:

    • IMetdataImporter
      • GetMemberProps (GetMemberProps是根据类型调用GetMethodProps或GetFieldProps的助手)
        • GetMethodProps
        • GetFieldProps
        • IMetdataImporter
          • GetMemberProps (GetMemberProps is a helper that calls GetMethodProps or GetFieldProps depending on the type)
            • GetMethodProps
            • GetFieldProps
            • MSDN博客:元数据非托管API (初步PDF据我所知，旧版Word文档的版本是Metadata API的唯一Microsoft文档) (推荐答案

              给出我想要的 Value 的枚举成员的 tokenID :

              Given the tokenID of an enumeration member i want the Value of:

              @0400043B = Windows.UI.Xaml.ApplicationHighContrastMode.Auto
              

              您需要遍历 Constant 表(0x0B)，并找到 Parent 列(columnIndex = 1)所在的位置.

              You need to iterate through the Constant table (0x0B), and find where the Parent column (columnIndex=1) is the element you want.

              常量表如下:

              Rid  Type (iBYTE)         Parent (iCodedToken)  Value (iBLOB)
              ===  ===================  ====================  ===============
              1    ELEMENT_TYPE_I4 (8)  @04000002             00 00 00 00
              2    ELEMENT_TYPE_I4 (8)  @04000003             01 00 00 00
              3    ELEMENT_TYPE_I4 (8)  @04000005             00 00 00 00
              ...
              883  ELEMENT_TYPE_I4 (8)  @0400040A             02 00 00 00
              884  ELEMENT_TYPE_U4 (9)  @0400043A             00 00 00 00
              885  ELEMENT_TYPE_U4 (9)  @0400043B             FF FF FF FF
              886  ELEMENT_TYPE_I4 (8)  @0400043D             00 00 00 00
              ...
              

              从IMetadataImporter开始，您需要 QueryInterface ，因为它是IMetadataTables界面:

              Starting with the IMetadataImporter, you need to QueryInterface for it's IMetadataTables interface:

              //Get the tables interface
              IMetadataTables tables = reader as IMetadataImporter;
              
              //get the number of rows in the Constant (11) table
              UInt32 tabConstant = 11; //the "Constant" table
              
              UInt32 rowSize;
              UInt32 rowCount;
              UInt32 columnCount;
              UInt32 keyColumn;
              String tableName;
              tables.GetTableInfo(tabConstant,
                     out rowSize,
                     out rowCount,
                     out columnCount,
                     out keyColumn,
                     out tableName);
              

              现在，在不进行Scunt工作的情况下，您实际上必须手动对表进行迭代:

              Now with the scunt work out of the way, you have to actually manually iterate the table:

              //Loop over ever row in the Constants table
              //and look for Parent (columnIndex=1) is the parent we want
              //all code released into the public domain; no attribution required
              UInt32 desiredToken = 0x0400043B;
              
              UInt32 colParent = 1; // Parent (iCodedToken)
              UInt32 colValue  = 2; // Value  (iBLOB)
              
              for (int i = 0 to rowCount-1)
              {
                 //Get the Parent codedToken of this row
                 UInt32 value;
                 tables.GetColumn(tabConstant, colParent, i, outvalue);
              
                 // Is it the parent we're interested in (i.e. @0400043A)
                 if (value != desiredToken)
                    continue;
              
                 // We found it! Get the value from the "Value" (iBLOB) column 2
                 tables.GetColumn(tabConstant, colValue, i, out value);
              
                 //Convert blob UInt32 to a pointer to data
                 UInt32 dataLen;
                 Pointer data;
                 tables.GetBlob(value, out dataLen, out dataLen, out data);
              
                 //Convert the dataLen bytes pointed to by data to a UInt32
                 UInt32 enumValue = PUInt32(data)^;
              
                 return enumValue;
              }
              

              这篇关于使用IMetadataImport时如何获取枚举值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！