Question

如何在类中的方法中更改Reference传递的参数的值？

即：

Public Class Setting

    Public Sub New(Optional ByRef target as String = Nothing)
        _target = target
    End Sub

    Private Sub Go()
        If Not IsNothing(_target) Then
            _target = "New Value"
        End If
    End Sub

End Class

用法：

Dim var1 as String = "Old Value"
Dim s as New Setting(var1)
s.Go()

在s.Go（）之后，我期待得到：

var1 = "New Value"

但我得到了：

var1 = "Old Value"

由于

Answer 1

使用包装类

例如，我使用StringBuilder作为包装类。

Public Class Setting
    Dim _target As StringBuilder
Public Sub New(Optional ByRef target as StringBuilder = Nothing)
    _target = target
End Sub

Private Sub ChangeValue()
    If Not IsNothing(_target) Then
        _target.Clear()
        _target.Append("New Value")
    End If
End Sub

Public Sub Go()
    ChangeValue()
End Sub

End Class
Sub Main()
    Dim var1 as New StringBuilder("Old Value")
    Dim s as New Setting(var1)
    s.Go()
    Console.WriteLine(var1)
End Sub

Answer 2

这个怎么样......

Public Sub New(Optional ByRef target as String = "")
    _target = target
End Sub

Private Sub ChangeValue()
    If _target.Length = 0 Then
        _target = "New Value"
    End If
End Sub

Answer 3

非常确定它必须像Mike C在评论

中所说的那样使字符串不可变

Strings (C# Programming Guide)

字符串对象是不可变的：它们具有后无法更改已创建。出现的所有String方法和C＃运算符修改字符串实际上会在新的字符串对象中返回结果。

使用Integer进行测试不是苹果，因为Integer是一种值类型

我怀疑=做了很深的复印件这是C＃
即使这样也不会将_s附加到s

public class Sclass
{
    public Sclass(ref string s)
    {
        s += "Sclass";
        string _s = s;
        _s += "_s";
    }
}

更改引用传递的参数的值

3 个答案: