Question

每当我尝试使用此循环时，它会崩溃并显示AmbiguousMatchException，但是当我将其更改为Do until k = 2时，代码运行没有问题。

Do Until k = 4
    i(k) = listview1.Items.Add(p(k, 0))
    With i(k)
        .SubItems.Add(p(k, 1))
        .SubItems.Add(p(k, 2))
        .SubItems.Add(p(k, 3))
        .SubItems.Add(p(k, 4))
    End With
    k = k + 1
Loop

我对VB.NET编码很新，但有人可以尝试解释这里的问题

Answer 1

我怀疑你的p值不是字符串或更多的原因是= Nothing。

示例：

Public Sub Bad()

    Dim listview1 As ListView = New ListView
    Dim t = Nothing
    Dim k As Integer = 0
    'Not Declared with a Type
    Dim p(,) = {{"string", "string", "string", "string", "string"}, _
                        {"string", "string", "string", "string", "string"}, _
                        {"string", "string", "string", "string", t}, _
                        {"10", "10", "test", "10", t}, _
                        {"10", "10", "test", "10", t}} 'Notice I added t as a value
    Dim i(4) As ListViewItem

    Do Until k = 4
        i(k) = listview1.Items.Add(p(k, 0))
        With i(k)
            .SubItems.Add(p(k, 1))
            .SubItems.Add(p(k, 2))
            .SubItems.Add(p(k, 3))
            .SubItems.Add(p(k, 4))
        End With
        k = k + 1
    Loop

End Sub

Public Sub Good()

    Dim listview1 As ListView = New ListView
    Dim t As String = Nothing
    Dim k As Integer = 0
    'Declared as String
    Dim p(,) As String = {{"string", "string", "string", "string", "string"}, _
                        {"string", "string", "string", "string", "string"}, _
                        {"string", "string", "string", "string", t}, _
                        {"10", "10", "test", "10", t}, _
                        {"10", "10", "test", "10", t}} 'Notice I added t as a value

    Dim i(4) As ListViewItem

    Do Until k = 4
        i(k) = listview1.Items.Add(p(k, 0))
        With i(k)
            .SubItems.Add(p(k, 1))
            .SubItems.Add(p(k, 2))
            .SubItems.Add(p(k, 3))
            .SubItems.Add(p(k, 4))
        End With
        k = k + 1
    Loop

End Sub

2个方法之间的唯一区别是P被声明为String而另一个不是。当您添加尚未转换的值时，ToString Reflection会对值的类型进行最佳猜测。如果反射无法确定过去的值是什么类型，因为它匹配多于1个类型，则抛出AmbiguousMatchException。

所以在这种情况下，t = Nothing Nothing的值可以等同于任何类型。正如您从下面的代码中看到的那样。

    Dim r = CType(Nothing, String)
    r = CType(Nothing, Integer)
    r = CType(Nothing, Object)
    r = CType(Nothing, Integer)

为了避免这种情况，最好在第一行添加：

Option Strict On

它将禁止后期绑定，并且不允许隐式输入

我的Array循环的VB.NET AmbiguousMatchException

1 个答案: