How to Check byte array empty or not?

Question

I am downloading the word file for GetSourceAttachment method. When this method returns empty bytes then my byte Attachment array gives an error:

Object reference not set instance of object

It gives the error when I check the length of Attachment in if condition.

Can any one help me to default initialize the byte array, then check the length?

try
{
        byte[] Attachment = null ;

        string Extension = string.Empty;
        ClsPortalManager objPortalManager = new ClsPortalManager();
        Attachment = objPortalManager.GetSourceAttachment(Convert.ToInt32(hdnSourceId.Value), out Extension);
        if (Attachment.Length > 0 && Attachment != null)
        {
            DownloadAttachment("Attacment", Attachment, Extension);
        }
        else
        {
            ClientScript.RegisterStartupScript(typeof(Page), "SymbolError", "<script type='text/javascript'>alert('Attachment is not Uploaded !');</script>");
        }            
}
catch
{

}

Soner Gönül · Accepted Answer · 2013-05-10 06:19:32Z

103

Just do

if (Attachment != null  && Attachment.Length > 0)

From && Operator

The conditional-AND operator (&&) performs a logical-AND of its bool operands, but only evaluates its second operand if necessary.

answered May 10, 2013 at 6:19

Soner Gönül

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Comments

Matthew Watson · Accepted Answer · 2021-02-09 10:05:15Z

26

You must swap the order of your test:

From:

if (Attachment.Length > 0 && Attachment != null)

To:

if (Attachment != null && Attachment.Length > 0 )

The first version attempts to dereference Attachment first and therefore throws if it's null. The second version will check for nullness first and only go on to check the length if it's not null (due to "boolean short-circuiting").

[EDIT] I come from the future to tell you that with later versions of C# you can use a "null conditional operator" to simplify the code above to:

if (Attachment?.Length > 0)

edited Feb 9, 2021 at 10:05

answered May 10, 2013 at 6:17

Matthew Watson

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Comments

Metin Atalay · Accepted Answer · 2016-11-14 08:59:38Z

21

.Net V 4.6 OR C # 6.0

Try This

 if (Attachment?.Length > 0)

answered Nov 14, 2016 at 8:59

Metin Atalay

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2 Comments

HellBaby Over a year ago

Maybe in 5 years our systems will recognize it... in my 4.6 framework project it's still compiles as an error.

René Kåbis Over a year ago

@HellBaby then you need to check the language associated with your project. Just because you are using DotNet 4.6 doesn’t mean that you are using C# >= 6. You could still be using C#5 for all you know. Go into your project's settings: right-click on project -> Properties -> Build -> Advanced and set the language explicitly to C# >= 6.

Habib · Accepted Answer · 2013-05-10 06:18:18Z

10

Your check should be:

if (Attachment != null  && Attachment.Length > 0)

First check if the Attachment is null and then lenght, since you are using && that will cause short-circut evaluation

&& Operator (C# Reference)

The conditional-AND operator (&&) performs a logical-AND of its bool operands, but only evaluates its second operand if necessary.

Previously you had the condition like: (Attachment.Length > 0 && Attachment != null), since the first condition is accessing the property Length and if Attachment is null, you end up with the exception, With the modified condition (Attachment != null && Attachment.Length > 0), it will check for null first and only moves further if Attachment is not null.

answered May 10, 2013 at 6:18

Habib

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2 Comments

SANDEEP Over a year ago

Thanks Thanks Thanks Habib....So much. but can you tell me what a issue with previous one plz

Habib Over a year ago

@SANDEEP, just modified the answer, for why you were getting the exception before

pejman · Accepted Answer · 2021-09-08 11:42:38Z

4

The best if statement in my opinion is this:

if(Attachment  is { Length: > 0 })

this code check both: null and length of the attachment

answered Sep 8, 2021 at 11:42

pejman

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Comments

jbdeguzman · Accepted Answer · 2019-11-13 05:04:39Z

0

Now we could also use:

if (Attachment != null  && Attachment.Any())

Any() is often easier to understand in a glance for the developer than checking Length() > 0. Also has very little difference with processing speed.

answered Nov 13, 2019 at 5:04

jbdeguzman

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1 Comment

Tolbxela Over a year ago

Yes, but .Any() is not internal method and adds a dependency to System.Linq (LINQ) library. LINQ is great, but for this simple action I wouldn't add an extra dependency.

Mangaldeep Singh Pannu · Accepted Answer · 2020-02-24 11:56:02Z

0

In Android Studio version 3.4.1

if(Attachment != null)
{
   code here ...
}

edited Feb 24, 2020 at 11:56

Mangaldeep Singh Pannu

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answered Feb 24, 2020 at 11:13

Ganesan J

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1 Comment

Tolbxela Over a year ago

The question was for C#. See the tag at bottom... ;-)

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