Question

如何使用本机方法将字符串转换为使用默认值的double？

这样的东西？

dim value as double
dim text

value = Double.TryParse(text, 0)

Answer 1

Dim text As String = "123.45"
Dim value As Double
If Double.TryParse(text, value) Then
    ' text is convertible to Double, and value contains the Double value now
Else
    ' Cannot convert text to Double set the default value here 
End If

Answer 2

这应该在一行中完成：

Dim value as Double
Dim text="23.675"

If Not Double.TryParse(text, value) Then value = 4
'At this point value contains either the parsed value of text 
'or 4 if text couldn't be parsed into a double

文档：http://msdn.microsoft.com/en-us/library/994c0zb1(v=vs.110).aspx

您当然可以使用默认值创建一个方法：

Public Function TryParseDoubleDefault(text as String, defaultValue as Double) As Double
    Dim parsedValue As Double
    If Not Double.TryParse(text, parsedValue) Then parsedValue = defaultValue
    Return parsedValue
End Function

你甚至可以将它作为Double的扩展方法：

<Extension()>
Public Function TryParseDefault(aDouble As Double, text as String, defaultValue as Double) As Double
    Dim parsedValue As Double
    If Not Double.TryParse(text, parsedValue) Then parsedValue = defaultValue
    Return parsedValue
End Function

这样你就可以按照原来的要求做到这一点：

value = Double.TryParseDefault(text, 4)

使用默认值将字符串转换为double

2 个答案: