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C#: List contains custom object

Posted on 2008-10-01
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Last Modified: 2013-12-17
Is there any way of using System.Collections.List.Contains() method to check if a collection of specific custom object has a given object, given that only one or few property (ies) of the object to look for are taken into account?
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Question by:karakav
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5 Comments
 
LVL 14

Expert Comment

by:Binuth
ID: 22613201
use System.Collections.List.Find()  to implement custom search
try this sample...
public class TestObject
{
	public TestObject()
	{
 
		System.Collections.Generic.List<testCalss> lstTestClass = new List<testCalss>();
 
		lstTestClass.Add(new testCalss(10 , 20));
		lstTestClass.Add(new testCalss(10 , 20));
		lstTestClass.Add(new testCalss(15 , 20));
 
		testCalss ObjClassFound;
		ObjClassFound = lstTestClass.Find(findObject);
 
	}
 
 
	public bool findObject(testCalss val)
	{
		if (val.iNumber1 == 15)
			return true;
		else
			return false;
	}
 
}
public class testCalss
{
	public Int32 iNumber1;
	public Int32 iNumber2;
	public testCalss(Int32 _iNumber1,Int32 _iNumber2)
	{
		this.iNumber1 = _iNumber1;
		this.iNumber2 = _iNumber2;
	}
}

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LVL 4

Author Comment

by:karakav
ID: 22613326
What if I want to pass the value to compare to in the findObject delegate?
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LVL 37

Accepted Solution

by:
gregoryyoung earned 500 total points
ID: 22615177
use an anonymous delegate or create a small wrapper class for your delegate.

There are plenty of examples of using anonymous delegates available on the web and the latter basically does the same thing by hand that the compiler does with an anonymous delegate.

class MyTestClassMatcher {
   private readonly int number1;
   private readonly int number2;

   public MyTestClassMatcher(int _number1, int _number2) {
       number1 = _number1;
       number2 = _number2;
   }

   public bool IsMatch(testCalss obj) {
         return obj.Number1 == number1 && obj.Number2 == number2;
   }
}

To use like in the example above

                lstTestClass.Add(new testCalss(10 , 20));
                lstTestClass.Add(new testCalss(10 , 20));
                lstTestClass.Add(new testCalss(15 , 20));
 
                MyClassFinder finder = new MyClassFinder(10, 20);
                ObjClassFound = lstTestClass.Find(finder.IsMatch);

to read more about how to use anonymous delegates for this check out http://msdn.microsoft.com/en-us/library/0yw3tz5k(VS.80).aspx


but basically it would be ...

public testClass SearchList(List<testClass>list, int value1, int value2) {
    return list.Find(delegate(testClass obj)
                             {
                                   return obj.number1 == value1 && obj.number2 == value2;
                             }
                          );
}

Cheers,

Greg
0
 
LVL 4

Author Closing Comment

by:karakav
ID: 31501912
Thanks a lot. This tip is really amazing.
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