String.Format：索引（从零开始）必须大于或等于零且小于参数列表的大小

Question

我正在尝试使用值数组格式化字符串：

Dim args(2) As Object
args(0) = "some text"
args(1) = "more text"
args(2) = "and other text"

Test(args)

函数测试是：

Function Test(ByVal args As Object)
    Dim MailContent as string = "Dear {0}, This is {1} and {2}."

    'tried both with and without converting arr to Array
    args = CType(args, Array)

    MailContent = String.Format(MailContent, args) 'this line throws the error: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.

End Function

Answer 1

为什么使用Object 作为args 的类型？你只是在扔掉你所有的类型信息。

Dim args As String() = {
    "some text",
    "more text",
    "and other text"
}

Test(args)

Sub Test(args As String())
    Dim mailTemplate As String = "Dear {0}, This is {1} and {2}."
    Dim mailContent As String = String.Format(mailTemplate, args)
End Sub

String.Format 接受 ParamArray 的对象，所以它会让你传递一个 (args; CType(a, T) 只是一个产生 T 类型值的表达式，不会神奇地改变类型的args，即使您转换为正确的类型）并将其视为单元素数组。

您可能还需要使用String.Format(mailTemplate, DirectCast(args, Object()))。我无法检查。