I don't know how many times I've written this code like this: if (string Variable!= null) int x = string Variable. Length; In Visual Basic I'd write this: If string Variable Is Not Nothing then Dim x as Integer x = string Variable. Length End If I test the string for null/nothing because if I try to get the Length of a variable set to null/ Nothing. well, I don't get the string's Length (null values don't have lengths). Instead, I get an exception. To simplify this block of code, both C 6.0 and Visual Basic 14 add a new operator that you can tack onto the end of a string (or other values the question mark (?). If the string that the operator is added to is null then the expression returns null and no further processing happens. This means that I could rewrite my previous code like this: int x = string Variable?. Length; If string Variable is set to null or Nothing, processing ends at the? mark and no attempt is made to retrieve the Length value. which means no exception is raised. However, my code still isn't right because, after all, the expression with the? operator has to return something. If my string is null then the? operator will return null. and my code has to handle that. The solution is to use a nullable data type to catch the result of my expression. For my example, the final code looks like this: Dim x As Integer? = string Variable?. Length Two other items: First, you can use the? operator with types other than strings. Second, if you think the? operator is useful, consider looking at the string object's Is Null Or White Space method. Posted by Peter Vogel on at 11:05 AM.
Category: C, VB. NET, ASP. NETType: Snippets Difficulty: Beginning Author: Rafiq Version Compatibility: Visual Basic. NET More information: Check for DBNull in VB. NET, with optional specification of type, so it converts null to the appropriate value (e.g., for string, 0 for numbers). Instructions: Copy the declarations and code below and paste directly into your VB project. Declarations: Code.
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