使整数为空 [英] Make An Integer Null

问题描述

我有一个更新函数，可以通过数据集更新 sql server db 表.表中的字段之一是整数并接受空值.因此，当我填充更新函数时，我需要一种方法来在函数需要整数时输入空值.

I have an update function that updates an sql server db table through a dataset. One of the fields in the table is an integer and accepts null values. So when I am populating the update function I need a way to enter a null in when the function wants an integer.

我尝试这样做，但 _intDLocation = "" 抛出异常

I tried to do it this way but _intDLocation = "" throws an exception

Dim _dLocation As String = udDefaultLocationTextEdit.Text
    Dim _intDLocation As Integer
    If _dLocation <> "" Then
        _intDLocation = Integer.Parse(udDefaultLocationTextEdit.Text)
    Else
        'NEED HELP HERE
        _intDLocation = ""
    End If

推荐答案

整数不能设置为 Null.您必须通过在单词 Integer 后添加问号使整数可空".现在 _intDLocation 不再是一个普通的整数.它是 Nullable(Of Integer) 的一个实例.

Integers cannot be set to Null. You have to make the integer "nullable" by adding a question mark after the word Integer. Now _intDLocation is no longer a normal integer. It is an instance of Nullable(Of Integer).

Dim _dLocation As String = udDefaultLocationTextEdit.Text
Dim _intDLocation As Integer?
If _dLocation <> "" Then
    _intDLocation = Integer.Parse(udDefaultLocationTextEdit.Text)
Else
    _intDLocation = Nothing
End If

稍后，如果你想检查 null，你可以使用这个方便、易读的语法:

Later on, if you want to check for null you can use this handy, readable syntax:

If _intDLocation.HasValue Then
   DoSomething()
End If

在某些情况下，您需要将值作为实际整数而不是可以为空的整数来访问.对于这些情况，您只需访问

In some cases you will need to access the value as an actual integer, not a nullable integer. For those cases, you simply access

_intDLocation.Value

在此处阅读有关 Nullable 的所有信息.

Read all about Nullable here.

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