Abstract Array Length?

Question

0.00/5 (No votes)

See more:

I have a variable of type object, which I know to contain an array. I know nothing about the contained type (it can vary), and neither I need to. All I want is to get the array size/length (number of elements in that array).

What is the right way of doing it in C#?

Posted 20-Dec-12 2:40am

Vitaly Tomilov

Add a Solution

5 solutions

Solution 4

Hi,

You can try this:

C#

int lengthOfArray = ((Array)obj).Length; // change obj into the name of your object

Hope this helps.

Posted 20-Dec-12 2:54am

Thomas Daniels

Updated 20-Dec-12 2:55am

v2

Comments

Vitaly Tomilov 20-Dec-12 9:17am

Good fix on your part, because the first version, suggesting use of (object[]obj).Length was no good, but use of Array works :)

Thomas Daniels 20-Dec-12 9:21am

Thank you!

Solution 1

its impossible to get the length without know the object is of type Array. You can check whether the object instance is of type array using 'is' operator and conver it using 'as' operator.

/Edit.
try casting the Object with ICollection and use the Count Property.

Posted 20-Dec-12 2:43am

Jibesh

Updated 20-Dec-12 2:57am

v2

Comments

Vitaly Tomilov 20-Dec-12 8:47am

I said in the question that I already know it is an array.

Jibesh 20-Dec-12 8:48am

oh.. my bad.. sorry.

Solution 5

C#

((ICollection)myObject).Count

(error handling omitted).

Posted 20-Dec-12 3:23am

CPallini

Updated 20-Dec-12 3:24am

v2

Comments

Thomas Daniels 20-Dec-12 9:25am

What you can add: The ICollection class in in the System.Collections namespace.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Pascal-78 · Accepted Answer · 2012-12-20T02:51:00

You can cast your object to Array

C#

object o = new int[3];
string test = (o as Array).Length.ToString();
MessageBox.Show(test);

or if it is a list:

C#

object o = new List<int>(3);
string test = (o as IList).Count.ToString();
MessageBox.Show(test)

and you can combine both using the operator is

C#

if(o is IList) size = (o as IList).Count;
if(o is Array) size = (o as Array).Length;

Update:
After test, int[] is IList too, but the List<int> is not Array, you may use the IList in all case

Vitaly Tomilov · Accepted Answer · 2012-12-20T02:52:00

Solution 3

I've just discovered that I can do the following trick that became possible only in .NET 4.0, using keyword dynamic:

C#

object obj; // We know it is an array, don't care about which type;
int arraySize = ((dynamic)obj).Length;

This seems to work fine. I wonder though, if there is any caveat to doing it... :)

Posted 20-Dec-12 2:52am

Vitaly Tomilov

Updated 20-Dec-12 2:53am

v2

Comments

Jibesh 20-Dec-12 9:00am

you can also use ICollection base.

lewax00 20-Dec-12 10:20am

If you're using it a lot, using dynamic might cause a performance hit (I'm pretty sure it uses reflection, which from what I've heard can be a little slow), otherwise it should be fine (and should even work if you later pass in a custom class, as long as it has an integer property called Length).

Abstract Array Length?

5 solutions

Solution 2

Solution 4

Solution 1

Solution 3

Solution 5

Add your solution here

Preview 0

Existing Members

...or Join us