Avoiding NullReferenceException in Request.QueryString

Question

This code throws a NullReferenceException if mode is not specified in the pages query string:

bool isAdvancedMode = Request.QueryString["mode"].Equals("advanced");

This is how I work around this:

bool isAdvancedMode = (Request.QueryString["mode"] + "").Equals("advanced");

Is this standard practise, or a hack?

Simon Belanger · Accepted Answer · 2013-07-18 15:06:09Z

7

You can use the null-coalescing operator:

bool isAdvancedMode = (Request.QueryString["mode"] ?? String.Empty).Equals("advanced");

Edit: If you want to re-use this logic, try this extension method:

public static bool EqualIfExists(this string source, string comparison)
{
    return source != null && source.Equals(comparison);
}

Request.QueryString["mode"].EqualIfExists("advanced")

Add more overrides to match Equals signature. I'm not sure if this is a good name (I think it is not).

edited Jul 18, 2013 at 15:06

answered Jul 18, 2013 at 14:51

Simon Belanger

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3 Comments

AndrewK Over a year ago

Nice. We'll see which one he picks!

Simon Belanger Over a year ago

Ahah. Last time @newStackExchangeInstance and I (like 30 minutes ago) answered the same questions 30 seconds apart, I won. I feel this one should go to him. So +1 to him. ;)

Tom Gullen Over a year ago

Thanks for answers, think this one goes to Simon as he was first to answer!

It'sNotALie. · Accepted Answer · 2013-07-18 14:52:10Z

4

Well, I would recommend this instead:

bool isAdvancedMode = (Request.QueryString["mode"] ?? "").Equals("advanced");

In fact, this is what your code compiles to (Nearer the bottom, but it's a good read so I'd read it all). Yours is good practice, but this is a bit more clear.

answered Jul 18, 2013 at 14:52

It'sNotALie.

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Comments

AndrewK · Accepted Answer · 2013-07-18 14:51:34Z

2

Why not use the null coalescing operator?

bool isAdvancedMode = (Request.QueryString["mode"] ?? String.Empty).Equals("advanced");

answered Jul 18, 2013 at 14:51

AndrewK

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3 Comments

It'sNotALie. Over a year ago

Well, actually, it compiles to the same code. Don't believe me? ericlippert.com/2013/06/17/…

AndrewK Over a year ago

I wasn't saying that it doesn't, just stating that the null-coalescing operator is more readable.

It'sNotALie. Over a year ago

I know, just interesting fact of the day :)

EkoostikMartin · Accepted Answer · 2013-07-18 14:53:21Z

0

Different approach, while a bit more code, I think is more clear the intent.

bool isAdvancedMode = String.IsNullOrWhitespace(Request.QueryString["mode"]) ? 
                        false : Request.QueryString["mode"].Equals("advanced")

answered Jul 18, 2013 at 14:53

EkoostikMartin

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2 Comments

Simon Belanger Over a year ago

While this is good, It feels dirty to me to access a dictionary value twice (even though it's O(1) in most cases). Also, it could be reduced to !String.IsNullOrWhitespace(Request.QueryString["mode"]) && Request.QueryString["mode"].Equals("advanced")

EkoostikMartin Over a year ago

@SimonBelanger good point about dictionary access, in that case I would use your ?? method myself too :)

Ehsan · Accepted Answer · 2013-07-18 14:54:35Z

0

what about this

bool isAdvancedMode=(Request.QueryString["mode"] ?? string.Empty).Equals("advanced");

answered Jul 18, 2013 at 14:54

Ehsan

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1 Comment

Tom Gullen Over a year ago

Looking for a one liner really as this problem is a common occurance

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