vb.net 检查DataTable是否有行的有效方法
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Efficient way to check if DataTable has row
提问by Angkor Wat
I have a function that search for a keyword and then return DataTable. I want to check if there rows inside because sometimes there's no query found.
我有一个搜索关键字然后返回 DataTable 的函数。我想检查里面是否有行，因为有时找不到查询。
'which one shoud I use ?
If dtDataTable Is Nothing Then
'some code
lbl_count.Text = "Found 0 result"
End If
If dtDataTable.Rows.Count > 0 Then
'some code
lbl_count.Text = "Found " & dtDataTable.Rows.Count.ToString & " results"
End If
Thanks.
谢谢。
回答by Steve Echols
How about:
怎么样：
If dtDataTable IsNot Nothing AndAlso dtDataTable.Rows.Count > 0 Then
'some code
lbl_count.Text = "Found " & dtDataTable.Rows.Count.ToString & " results"
Else
'some code
lbl_count.Text = "Found 0 result"
End If
回答by JaredPar
If you're using VB 9.0 (VS 2008) you can simply this with the following
如果您使用的是 VB 9.0 (VS 2008)，您可以简单地使用以下命令
lbl_count.Text = String.Format("Found {0} result(s)", if(dbDataTable, dbDataTable.Rows.Count,0))
回答by thisismydisplayname
Steve Echols got both the nails on their heads and just so you know the Andalsochecks the first condition and if the first condition fails then a FALSE is returned; if the first condition is TRUE then and only then does it check the second condition.
Steve Echols 把两个钉子都钉在了他们的头上，所以你知道Andalso检查第一个条件，如果第一个条件失败，则返回 FALSE；如果第一个条件为 TRUE，那么它才会检查第二个条件。
this way John Boker's point is also taken care of!
这样约翰·博克的观点也得到了照顾！
Kudos to both!
为两人点赞！
回答by John Boker
You should use the second, i dont think the first would work, and if it did the second would not work because dtDataTable.Rows would throw a null reference exception.
你应该使用第二个，我不认为第一个会起作用，如果它起作用，第二个将不起作用，因为 dtDataTable.Rows 会抛出一个空引用异常。
