Question

我正试图在P / Invoking之前找到检测某个功能是否存在的好方法。例如，调用本机StrCmpLogicalW函数：

[SuppressUnmanagedCodeSecurity]
internal static class SafeNativeMethods
{
   [DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
   public static extern int StrCmpLogicalW(string psz1, string psz2);
}

会在某些没有此功能的系统上崩溃。

i don't want to perform version checking，因为这是不好的做法，有时可能是错误的（例如，当功能被反向移植时，或者可以卸载功能时）。

正确的方法是从shlwapi.dll检查导出的状态：

private static _StrCmpLogicalW: function(String psz1, String psz2): Integer;
private Boolean _StrCmpLogicalWInitialized;

public int StrCmpLogicalW(String psz1, psz2)
{
    if (!_StrCmpLogialInitialized)
    {
        _StrCmpLogicalW = GetProcedure("shlwapi.dll", "StrCmpLogicalW");
        _StrCmpLogicalWInitialized = true;
    }

    if (_StrCmpLogicalW)
       return _StrCmpLogicalW(psz1, psz2)
    else
       return String.Compare(psz1, psz2, StringComparison.CurrentCultureIgnoreCase);
}

问题当然是C＃不支持函数指针，即：

_StrCmpLogicalW = GetProcedure("shlwapi.dll", "StrCmpLogicalW");

无法完成。

所以我试图找到替代语法来在.NET中执行相同的逻辑。到目前为止我有以下伪代码，但我受到了阻碍：

[SuppressUnmanagedCodeSecurity]
internal static class SafeNativeMethods
{
   private Boolean IsSupported = false;
   private Boolean IsInitialized = false;

   [DllImport("shlwapi.dll", CharSet = CharSet.Unicode, Export="StrCmpLogicalW", CaseSensitivie=false, SetsLastError=true, IsNative=false, SupportsPeanutMandMs=true)]
   private static extern int UnsafeStrCmpLogicalW(string psz1, string psz2);

   public int StrCmpLogicalW(string s1, string s2)
   {
       if (!IsInitialized) 
       {
          //todo: figure out how to loadLibrary in .net
          //todo: figure out how to getProcedureAddress in .net
          IsSupported = (result from getProcedureAddress is not null);
          IsInitialized = true;
       }

       if (IsSupported) 
          return UnsafeStrCmpLogicalW(s1, s2);
       else
          return String.Compare(s1, s2, StringComparison.CurrentCultureIgnoreCase);
   }
}

我需要一些帮助。

我希望检测存在的某些导出的另一个例子是：

dwmapi.dll::DwmIsCompositionEnabled
dwmapi.dll::DwmExtendFrameIntoClientArea
dwmapi.dll::DwmGetColorizationColor
dwmapi.dll::DwmGetColorizationParameters（未记录的¹，尚未按名称导出，序号为127）
dwmapi.dll::127（未记录¹，DwmGetColorizationParameters）

自Windows 7 SP1起

¹

.NET中必须已有一个设计模式来检查操作系统功能的存在。有人能指出我在.NET中执行特征检测的首选方法的例子吗？

Answer 1

您可以P / Invoke到LoadLibraryW加载shlwapi.dll然后P / Invoke到GetProcAddressW以找到“StrCmpLogicalW”。如果返回NULL，那么它就不存在。

您不需要GetProcAddressW的实际返回值 - 只要它不是NULL，您就知道可以使用您选择的P / Invoke声明。

请注意，GetProcAddressW还支持按序数值导出的函数。

编辑：如果您想要遵循某种模式，那么这可能会有效：

首先定义一个帮助器类NativeMethodResolver，它告诉您库中是否存在方法：

public static class NativeMethodResolver
{
    public static bool MethodExists(string libraryName, string methodName)
    {
        var libraryPtr = LoadLibrary(libraryName);
        var procPtr = GetProcAddress(libraryPtr, methodName);

        return libraryPtr != UIntPtr.Zero && procPtr != UIntPtr.Zero;
    }

    [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    private static extern UIntPtr LoadLibrary(string lpFileName);

    [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Ansi)]
    private static extern UIntPtr GetProcAddress(UIntPtr hModule, string lpProcName);
}

上面的辅助类可以被SafeNativeMethod的派生类使用，这有助于锅炉电镀一些常见的东西：

public abstract class SafeNativeMethod
{
    private readonly string libraryName;
    private readonly string methodName;
    private bool resolved;
    private bool exists;

    protected SafeNativeMethod(string libraryName, string methodName)
    {
        this.libraryName = libraryName;
        this.methodName = methodName;
    }

    protected bool CanInvoke
    {
        get
        {
            if (!this.resolved)
            {
                this.exists = Resolve();
                this.resolved = true;
            }

            return this.exists; 
        }            
    }

    private bool Resolve()
    {
        return NativeMethodResolver.MethodExists(this.libraryName, this.methodName);
    }
}

定义自己的Invoke方法的派生类可以调用基类CanInvoke以查看是否应该返回默认值（或默认实现）来代替所寻找的本机的返回值方法。根据您的问题，我将 shlwapi.dll / StrCmpLogicalW 和 dwmapi.dll / DwmIsCompositionEnabled 作为SafeNativeMethod的示例实现：

public sealed class SafeStrCmpLogical : SafeNativeMethod
{
    public SafeStrCmpLogical()
        : base("shlwapi.dll", "StrCmpLogicalW")
    {           
    }

    public int Invoke(string psz1, string psz2)
    {
        return CanInvoke ? StrCmpLogicalW(psz1, psz2) : 0;
    }

    [DllImport("shlwapi.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    private static extern int StrCmpLogicalW(string psz1, string psz2);
}

public sealed class SafeDwmIsCompositionEnabled : SafeNativeMethod
{
    public SafeDwmIsCompositionEnabled()
        : base("dwmapi.dll", "DwmIsCompositionEnabled")
    {
    }

    public bool Invoke()
    {
        return CanInvoke ? DwmIsCompositionEnabled() : false;
    }

    [DllImport("dwmapi.dll", SetLastError = true, PreserveSig = false)]
    private static extern bool DwmIsCompositionEnabled();
}

然后可以像这样使用这两个：

static void Main()
{
    var StrCmpLogical = new SafeStrCmpLogical();
    var relation = StrCmpLogical.Invoke("first", "second");

    var DwmIsCompositionEnabled = new SafeDwmIsCompositionEnabled();
    var enabled = DwmIsCompositionEnabled.Invoke();
}

P /调用C＃和.NET时的功能检测

1 个答案: