ArrayList Contains

[HarvSather]

C# VS2005

I have a class with 5 properties

I am adding instances this class to an ArrayList

I want to test to see if an instance is already in the ArrayList before
attempting to add the item

From my reading, it seems that I have to have an Equals method in my class

I have created an Equals method, but it is never called

Does anyone have some insight into my problem?

TIA

Harvey Sather
Saskatoon Canada

[Michael C]

"HarvSather" <ha********@msn.com> wrote in message
news:uH**************@TK2MSFTNGP02.phx.gbl...

C# VS2005

I have a class with 5 properties

I am adding instances this class to an ArrayList

I want to test to see if an instance is already in the ArrayList before
attempting to add the item

From my reading, it seems that I have to have an Equals method in my class
You don't have to have an equals method. It will match on the instance if
you don't. You only need the equals if you want something more advanced.
I have created an Equals method, but it is never called

Did you use the override keyword? If you don't use this it will not be
called.

Michael

[Michael Nemtsev]

Hello HarvSather,

You need compare classes' member not the classes instances.
H> C# VS2005
H> I have a class with 5 properties
H> I am adding instances this class to an ArrayList
H> I want to test to see if an instance is already in the ArrayList
H> before attempting to add the item
H> From my reading, it seems that I have to have an Equals method in my
H> class
H> I have created an Equals method, but it is never called
H> Does anyone have some insight into my problem?

---
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour

"At times one remains faithful to a cause only because its opponents do not
cease to be insipid." (c) Friedrich Nietzsche

[HarvSather]

In the Equals method, I compare the properties of two instances.
I want to know if one instance is the same as another.
The thing that tells me that is if one of the properties in each instance is
equal.

The thing is, the equals method never gets called.

So, I am not sure if we are talking about the same thing.

Do you have some sample "working" code that you can post?

Thanks


"Michael Nemtsev" <ne*****@msn.com> wrote in message
news:9c**************************@msnews.microsoft .com...

Hello HarvSather,

You need compare classes' member not the classes instances.
H> C# VS2005
H> I have a class with 5 properties
H> I am adding instances this class to an ArrayList
H> I want to test to see if an instance is already in the ArrayList
H> before attempting to add the item
H> From my reading, it seems that I have to have an Equals method in my
H> class
H> I have created an Equals method, but it is never called
H> Does anyone have some insight into my problem?

---
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour

"At times one remains faithful to a cause only because its opponents do
not cease to be insipid." (c) Friedrich Nietzsche

[HarvSather]

Well, I found the answer

I was declaring the Equals method with the wrong signature

Initially I had
public bool Equals(clsValueListItems vobjItem)

but it should be
public override bool Equals(object vobjItem)

The parameter must be a generic object rather than a specific type
Then you can cast it to a local variable and of the type you want
The whole Equals method looks like this in my class

public override bool Equals(object vobjItem)
{
if (vobjItem == null || GetType() != vobjItem.GetType())
return false;

clsValueListItems lobjItem = (clsValueListItems)vobjItem;
bool lblnIsContained = false;

if (lobjItem.ItemDataString == mstrItemData ||
(lobjItem.ItemDataInt == mintItemData && mintItemData != -10))
lblnIsContained = true;

return lblnIsContained;
}
The Contains method of an ArrayList uses the Equals method of the class to
determine if the item is in the list.
You have to override the base Equals method so that it works for the class
your are using

Harvey Sather
Saskatoon Canada



"HarvSather" <ha********@msn.com> wrote in message
news:uD**************@TK2MSFTNGP04.phx.gbl...

In the Equals method, I compare the properties of two instances.
I want to know if one instance is the same as another.
The thing that tells me that is if one of the properties in each instance
is equal.

The thing is, the equals method never gets called.

So, I am not sure if we are talking about the same thing.

Do you have some sample "working" code that you can post?

Thanks


"Michael Nemtsev" <ne*****@msn.com> wrote in message
news:9c**************************@msnews.microsoft .com...

Hello HarvSather,

You need compare classes' member not the classes instances.
H> C# VS2005
H> I have a class with 5 properties
H> I am adding instances this class to an ArrayList
H> I want to test to see if an instance is already in the ArrayList
H> before attempting to add the item
H> From my reading, it seems that I have to have an Equals method in my
H> class
H> I have created an Equals method, but it is never called
H> Does anyone have some insight into my problem?

---
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour

"At times one remains faithful to a cause only because its opponents do
not cease to be insipid." (c) Friedrich Nietzsche

[Greg Young]

There might be a problem here with some of your code ...

if (vobjItem == null || GetType() != vobjItem.GetType())
return false;

What if I later what to subclass your type?

The following code should be a bit more friendly with polymorphism ..

clsValueListItems tmp = vobjItem as clsValueListItems;
if(tmp == null) {
return false;
}
//continue as normal.
Cheers,

Greg Young
MVP - C#

"HarvSather" <ha********@msn.com> wrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

Well, I found the answer

I was declaring the Equals method with the wrong signature

Initially I had
public bool Equals(clsValueListItems vobjItem)

but it should be
public override bool Equals(object vobjItem)

The parameter must be a generic object rather than a specific type
Then you can cast it to a local variable and of the type you want
The whole Equals method looks like this in my class

public override bool Equals(object vobjItem)
{
if (vobjItem == null || GetType() != vobjItem.GetType())
return false;

clsValueListItems lobjItem = (clsValueListItems)vobjItem;
bool lblnIsContained = false;

if (lobjItem.ItemDataString == mstrItemData ||
(lobjItem.ItemDataInt == mintItemData && mintItemData != -10))
lblnIsContained = true;

return lblnIsContained;
}
The Contains method of an ArrayList uses the Equals method of the class to
determine if the item is in the list.
You have to override the base Equals method so that it works for the class
your are using

Harvey Sather
Saskatoon Canada



"HarvSather" <ha********@msn.com> wrote in message
news:uD**************@TK2MSFTNGP04.phx.gbl...

In the Equals method, I compare the properties of two instances.
I want to know if one instance is the same as another.
The thing that tells me that is if one of the properties in each instance
is equal.

The thing is, the equals method never gets called.

So, I am not sure if we are talking about the same thing.

Do you have some sample "working" code that you can post?

Thanks


"Michael Nemtsev" <ne*****@msn.com> wrote in message
news:9c**************************@msnews.microsoft .com...

Hello HarvSather,

You need compare classes' member not the classes instances.
H> C# VS2005
H> I have a class with 5 properties
H> I am adding instances this class to an ArrayList
H> I want to test to see if an instance is already in the ArrayList
H> before attempting to add the item
H> From my reading, it seems that I have to have an Equals method in my
H> class
H> I have created an Equals method, but it is never called
H> Does anyone have some insight into my problem?

---
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour

"At times one remains faithful to a cause only because its opponents do
not cease to be insipid." (c) Friedrich Nietzsche

[Nick Hounsome]

"HarvSather" <ha********@msn.com> wrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

Well, I found the answer

I was declaring the Equals method with the wrong signature

Initially I had
public bool Equals(clsValueListItems vobjItem)

but it should be
public override bool Equals(object vobjItem)

Always use intellisense - it saves a lot of problems - You can start the
line with "override" rather than public and it will sort it all out nicely
for you when you've decided what you are overriding.

Of course if you had put override in anyway the compiler would have told you
that you weren't overriding anything.

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

Why don't you use one of the generic implementations?

You can use ArrayList.Contains , if does use Equals . So yes, you need to
have an Equals method in your class.

Can you post your Equals ethod?

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

"HarvSather" <ha********@msn.com> wrote in message
news:uH**************@TK2MSFTNGP02.phx.gbl...

C# VS2005

I have a class with 5 properties

I am adding instances this class to an ArrayList

I want to test to see if an instance is already in the ArrayList before
attempting to add the item

From my reading, it seems that I have to have an Equals method in my class

I have created an Equals method, but it is never called

Does anyone have some insight into my problem?

TIA

Harvey Sather
Saskatoon Canada

[Chris Dunaway]

Take a look at the IEquatable<T> interface. Perhaps that will help.