C# ASP.NET错误处理-在Global.asax中未检测到正确的错误类型

我定义了一些自定义错误类，每个类都有自己的功能（未显示）：

例外。cs

public abstract class MyAppException : Exception {
  //...
}
public class ValidationException : MyAppException {
  //...
}
public class AccessDeniedException : MyAppException {
  //...
}

protected void Page_Load(object sender, EventArgs e)
{
  throw new AccessDeniedException();
}

protected void Application_Error(object sender, EventArgs e) {
  var exc = Server.GetLastError();
  if (exc is MyAppException) ((MyAppException)exc).Log();
}

现在，在空白页的代码隐藏中，我有：

test.aspx.cs

public abstract class MyAppException : Exception {
  //...
}
public class ValidationException : MyAppException {
  //...
}
public class AccessDeniedException : MyAppException {
  //...
}

protected void Page_Load(object sender, EventArgs e)
{
  throw new AccessDeniedException();
}

protected void Application_Error(object sender, EventArgs e) {
  var exc = Server.GetLastError();
  if (exc is MyAppException) ((MyAppException)exc).Log();
}

我的目的是在应用程序级别了解这一点：

Global.asax.cs

public abstract class MyAppException : Exception {
  //...
}
public class ValidationException : MyAppException {
  //...
}
public class AccessDeniedException : MyAppException {
  //...
}

protected void Page_Load(object sender, EventArgs e)
{
  throw new AccessDeniedException();
}

protected void Application_Error(object sender, EventArgs e) {
  var exc = Server.GetLastError();
  if (exc is MyAppException) ((MyAppException)exc).Log();
}

但是通过添加断点，我发现

exc is MyAppException

的计算结果为

false

---

我哪里出错了？

尝试内部异常：

if (exc.InnerException is MyAppException)

是

System.Web.UI.Page.HandleError

方法将实际异常包装到

HttpUnhandledException

中