如何缩短If ... Else ...语句以检查Date的状态？

Question

I am a C# programmer but dabbling in VB.Net because everybody else in my team uses it. In the interests of professional development I would like to shrink the following If... Else... statement.

If cmd.Parameters("@whenUpdated").Equals(DBNull.Value) Then
    item.WhenUpdated = Nothing
Else
    item.WhenUpdated = cmd.Parameters("@whenUpdated").Value
End If

I appreciate examples are already available however I can not get it working for this specific case.

Cheers, Ian.

Answer 1

使用If作为函数而不是语句：

item.WhenUpdated = If(cmd.Parameters("@whenUpdated").Equals(DBNull.Value), cmd.Parameters("@whenUpdated").Value, Nothing)

Answer 2

Similar to the ternary operator in C#, VB has the IIF function .

item.WhenUpdated = IIF(cmd.Parameters("@whenUpdated").Equals(DBNull.Value),
                            cmd.Parameters("@whenUpdated").Value, 
                            Nothing)

If the first argument (the boolean expression) evaluates to true, then the second argument is returned from the function. If the first argument is false, then the third argument is returned.

Answer 3

item.WhenUpdated = Nothing
If cmd.Parameters("@whenUpdated").Equals(DBNull.Value) Then
    item.WhenUpdated = cmd.Parameters("@whenUpdated").Value
End If

Only 1 line, but still shorter.

The IF function is definitely the shortest, but not the most readable.

Answer 4

One less line

item.WhenUpdated = Nothing
If cmd.Parameters("@whenUpdated").Equals(DBNull.Value) Then
    item.WhenUpdated = cmd.Parameters("@whenUpdated").Value
End If

Answer 5

Use the operator If(...) if you want short-circuiting behavior.

Use the function IIf(...) if you don't want short-circuiting behavior.