Queue.Contains(myobj) return always false..

[semedao]

Hi
I have some Queue object that I enqueue other objects into it.
I want to check if someobject already exists before enqueue , using the
Contains method
but italways return false.
in the object that I enqueue I implement CompareTo method (Icompareable)
but the debugger doesn't go there...
thanks

 

[Walter Wang [MSFT]]

Hi,

Queue.Contains internally uses Object.Equals() to determine whether or not
two object instances are equal. So I think you need to override the Equals
method in your object like the following example:

public class Foo
{
public int id;

public override bool Equals(object obj)
{
if (obj is Foo)
{
return (obj as Foo).id == id;
}
return false;
}
}

class Program
{
static void Main(string[] args)
{
Queue q = new Queue();
Foo f1 = new Foo();
f1.id = 1;
Foo f2 = new Foo();
f2.id = 1;
q.Enqueue(f1);
if (q.Contains(f2))
{
Console.WriteLine("contains");
}
}
}

I hope this helps. Please feel free to post here if anything is unclear.

Sincerely,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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[Glenn]

You can override the Equals and GetHashCode methods.

public class TestClass
{
public DateTime _time;
public string _name;

public TestClass( DateTime time, string name )
{
_time = time;
_name = name;
}

public override bool Equals( object obj )
{
TestClass tc = obj as TestClass;

return tc._name == this._name;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}

It'll work without overriding GetHashCode, but you'll get a warning.

HTH

Glenn

 

[Stoitcho Goutsev \(100\)]

semedao,

Queue.Contains uses Equals method to compare items. You should override
this method if you need to provide custom comparition. If you decide to do
this read MSDN article for Object.Equals method. There are the requirements
for this method when overriden.

It is realy strange that it doesn't work though. Can you post a compilable
sample that demonstrates the problem?

 

[Walter Wang [MSFT]]

Hi semedao,

What do you think of the replies above? Please feel free to post here if
anything is unclear.

Regards,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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[semedao]

Thanks , I override it and it'swork , but some confused why to override
twice the same method , one by implementing IEquatable , and other for
regular...

 

[Walter Wang [MSFT]]

Hi,

The generic interface IEquatable is an interface which will compare an
object against another object to see if they are equal. It has one method
for you to implement, the Equals( T obj ) method. This is pretty similar
to the System.Object.Equals method you maybe thinking, but the difference
is that the Object.Equals method that all classes have, is not type
specific, while the IEquatable interface is a generic type and will be
type-safe. When thinking about value types this comes into play even more
because with the Object.Equals, we have to box/unbox those values in order
to compare them, while our type-safe version of IEquatable will not need to
box the value type.

If you are using generic version of Queue<>, then either overriding
Object.Equals or implementing IEquatable<> will work. But the latter is
recommended since it has better performance. If you are using non generic
version of Queue, then only overriding Object.Equals will work.

Regards,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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[Walter Wang [MSFT]]

Hi Semedao,

Did my previous reply answer your question? Please reply here to let me
know whether you need further information. Thank you.

Regards,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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that others may learn and benefit from your issue.
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[semedao]

Yes , thank you
I need to implement the regular equals , because I can't use the generic
queue in the place I need it.