.net – 构造函数链接和空引用测试

说：

' class MyHoyr '
  Public Sub New(ByVal myHour As MyHour)
    ' Can't doing it here !!!! '
    If myHour Is Nothing Then Throw New ArgumentNullException("myHour")

    ' Constructor call should be first '
    Me.New(myHour._timeSpan)

    ' Here is too late... '
  End Sub


  Private Sub New(ByVal timeSpan As TimeSpan)
    '.... '
  End Sub

public MyHour(MyHour myHour) : this(GetTimeSpan(myHour))
{}

private static TimeSpan GetTimeSpan(MyHour myHour)
{
    if(myHour== null) throw new ArgumentNullException("myHour");
    return myHour._timeSpan;
}

private MyHour(TimeSpan timeSpan)
{...}

我假设你可以在VB中做一些非常相似的事情. (共享方法？)

反射器向我保证这转化为：

Public Sub New(ByVal myHour As MyHour)
    Me.New(MyHour.GetTimeSpan(myHour))
End Sub

Private Sub New(ByVal timeSpan As TimeSpan)
End Sub

Private Shared Function GetTimeSpan(ByVal myHour As MyHour) As TimeSpan
    If (myHourIs Nothing) Then
        Throw New ArgumentNullException("myHour")
    End If
    Return myHour._timeSpan
End Function