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Trick when using Array.Contains() C# 2.0

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Wouldn’t it be nice if you could test whether an element is contained in an array by using a Contains method just like the one available on List objects? Wouldn’t it be good if you could write code like this?
string[] stuff = ....;
if (stuff.Contains(“item”))
{
    ...
}

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In .NET 3.5, this is possible out of the box (make sure you reference System.Core and include the System.Linq namespace) but if you try to run this code in .NET 2.0 or .NET 3.0, you will get errors. Nevertheless the .NET Framework 2.0 does provide a Contains() method on any Array object.

In the .NET Framework 2.0, System.Array implements the System.Collections.Generic.IList<T> interface. Unfortunately the implementation of the IList interface is provided at runtime, so we do not see the methods in Visual Studio and we cannot write array.Contains().

Instead, we have to cast the array to the appropriate IList interface:

string[] arr = new string[] { “RR US”, “RR India”, “RR UK” };
if (!((IList<string>)arr).Contains(“India”))
{
     System.Console.WriteLine ("Correct! We are working with RR India");
}

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The documentation explains it as follows:

In the .NET Framework version 2.0, the Array class implements the System.Collections.Generic.IList, System.Collections.Generic.ICollection, and System.Collections.Generic.IEnumerable generic interfaces. The implementations are provided to arrays at run time, and therefore are not visible to the documentation build tools. As a result, the generic interfaces do not appear in the declaration syntax for the Array class, and there are no reference topics for interface members that are accessible only by casting an array to the generic interface type (explicit interface implementations). The key thing to be aware of when you cast an array to one of these interfaces is that members which add, insert, or remove elements throw NotSupportedException.


So next time, you can save yourself from writing (unnecessary) code like this:

bool found =false;
    foreach (string s in array)
    {
        if (s.Equals(“item”))
        {
            found =true;
            break;
        }
    }
    if (found)
    {
       ........
    }

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Some of you guys might have an alternate solution for this.
For example

bool exists = Array.IndexOf(arr, "RR India") >= 0

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No doubt this is an alternative solution solutions. This may differ in terms of performance. But, this is for c# 2.0 and as explained above .NET Framework 2.0 does provide a Contains() method on any Array object. So this may helpful for framework wise comparison.

Happy Programming!!!
4
Comment
5 Comments
 

Expert Comment

by:RETAILREALM
This is good stuff. Great work!!!
0
 
LVL 18

Expert Comment

by:Rajar Ahmed
always good to have plan b for any solution .
i will definitely use this in future ...
thanks..
0
 
LVL 1

Expert Comment

by:apuma
I have found that in some cases using a dictionary object is useful, (as of 3.5?) you can call contains , or countainsKey to check either objects or keys. and since it is a based on a hashmap, the containskey is extremely fast in large lists [compared to standard arrays, lists].  since the dictionary constructor specifies the object type for the list you also maintain all the intelisense for the objects, as apposed to a standard hashmap (or is it hashtable?) which only returns Object class Objects
0
 
LVL 17

Expert Comment

by:nepaluz
The problem you describe is NOT limited to .NET 2.0, infact, the same happens with .NET 4.5 on arrays and arraylists. Lists dynamically typecast values inside them in LINQ whereas this is not the case with arrays. The cure you prescribe, though, is correct.
0
 
LVL 16

Expert Comment

by:Easwaran Paramasivam
Good findings!!
0

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