IEnumerator IEnumerable vb 到 C#

Question

大家好，我是 c# 语言的新手，我使用的是 vb.net， 在下面这段代码有什么错误以及为什么，谢谢

vb.net code
Class SplitString
Implements IEnumerable
Implements IEnumerator

Private currentPosition As Integer = 0
Private m_Sentence As String
Property Sentence() As String
    Get
        Return m_Sentence
    End Get
    Set(ByVal Value As String)
        m_Sentence = Value
        Me.Reset()
    End Set
End Property

Public ReadOnly Property Current As Object Implements IEnumerator.Current
    Get
        Dim counter As Integer
        Dim tmpLength As Integer = 0
        For counter = Me.currentPosition To Me.Sentence.Length - 1
            If Me.Sentence.Chars(counter) = " "c Then
                Exit For
            Else
                tmpLength += 1
            End If
        Next
        Current = Me.Sentence.Substring(Me.currentPosition, tmpLength) ' ok 
        Me.currentPosition += tmpLength + 1
    End Get
End Property

Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
    If Me.currentPosition > Me.Sentence.Length - 1 Then
        Me.Reset()
        Return False
    Else
        Return True
    End If
End Function

Public Sub Reset() Implements IEnumerator.Reset
    Me.currentPosition = 0
End Sub

Public Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
    Return Me
End Function
End Class

但是当我尝试这个代码到 c# 时，我得到了错误

c# code
class SplitString:IEnumerable,IEnumerator
{
    private int currentPosition = 0;
    private string m_Sentence;
    public string Sentence
    {
        get { return m_Sentence; }
        set
        {
            m_Sentence = value;
            this.Reset();
        }
    }
    public IEnumerator GetEnumerator()
    {
        return this;
    }


    public object Current
    {
        get
        {
            int counter = 0;
            int tmpLength = 0;
            for (counter = this.currentPosition; counter <= this.Sentence.Length - 1; counter++)
            {
                if (this.Sentence[counter] == ' ')
                {
                    break; 
                }
                else
                {
                    tmpLength += 1;
                }
            }
            Current = this.Sentence.Substring(this.currentPosition, tmpLength); // Error
            this.currentPosition += tmpLength + 1;
            return functionReturnValue;
        }
    }
    public bool MoveNext()
    {
       if (this.currentPosition > this.Sentence.Length-1)
       {
           this.Reset();
           return false;
       }
       else
       {
           return true;
       }
    }

    public void Reset()
    {
        this.currentPosition=0;
    }
}

错误：无法将属性或索引器“Example.splitstring.current”分配给——它是只读的

Answer 1

（出于 VB6 向后兼容性/遗留原因）VB.NET 允许您通过将 Function/Property 名称设置为一个值来从 Property 或 Function 返回值。

来自文档：Function Procedures

"... 过程以两种方式之一返回此值：..."

• "...它为自己的函数名赋值一个或多个 程序的陈述。控制不返回调用 程序直到退出函数或结束函数语句 执行...”

例如

Public Function TestFunc() As String
    TestFunc = "bar"
    'some code
End Function

这大致相当于：

Public Function TestFunc() As String
    Dim temp = "bar"
    'some code
    Return temp
End Function

所以在您的 VB 代码中，它设置了属性名称以返回一个值：

Public ReadOnly Property Test As String
    Get
        Test = "foo"
    End Get
End Property

或者在你的情况下：

Current = Me.Sentence.Substring(Me.currentPosition, tmpLength)

在 C# 中没有与此等效的 direct，因为 return 会立即返回。最好的所以等效的 C# 将设置一个临时变量并返回：

var temp= this.Sentence.Substring(this.currentPosition, tmpLength);
//some more code
return temp;

每当我从 VB 的类中访问一个属性时，我总是在我的属性前加上 Me.，这样可以避免这种讨厌的行为

Answer 2

这个

Current = Me.Sentence.Substring(Me.currentPosition, tmpLength) ' ok 

是在不使用Return 关键字的情况下在方法中设置返回值的“旧”VB 方式。一般来说，下面的VB代码

    myMethodName = ...
    ...some other code...
End Function

可以改写为

    Dim someTempVariable = ...
    ...some other code...
    Return someTempVariable
End Function

（只要some other code 不退出方法）。

属性也是如此。因此，我们首先将您的旧 VB 代码重写为新 VB 代码：

        ...
    Next
    Dim returnValue = Me.Sentence.Substring(Me.currentPosition, tmpLength) 
    Me.currentPosition += tmpLength + 1
    Return returnValue
End Get

现在对 C# 的翻译应该很明显了。

Answer 3

您还没有为Current 属性声明set 块，因此它是只读的。您需要实现它，例如：

public object Current
{
    get
    {
        int counter = 0;
        int tmpLength = 0;
        for (counter = this.currentPosition; counter <= this.Sentence.Length - 1; counter++)
        {
            if (this.Sentence[counter] == ' ')
            {
                break; 
            }
            else
            {
                tmpLength += 1;
            }
        }
        Current = this.Sentence.Substring(this.currentPosition, tmpLength); // Error
        this.currentPosition += tmpLength + 1;
        return functionReturnValue;
    }
    set
    {
        this.Current = value;
    }
}

Answer 4

您的 Current 和 functionReturnValue 变量未在您的代码中定义，请在函数中定义。

   Current = this.Sentence.Substring(this.currentPosition, tmpLength); // Error
   return functionReturnValue;