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Overriding Equals method not being called when doing IndexOf an item in an ArrayList

From reading the documentation, this should be a relatively easy thing. I
have an arraylist of custom class instances which I want to search with
an"indexof" where I'm passing an instance if the class where only the
"searched" property has a value. I expected to get the index into the
arraylist where I could then get the entire class instance. However, the
'indexof' is never calling my overloaded, overrides Equals method. Here is
the code snippet:

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load

Dim PeopleCollectio n As New ArrayList

Dim Customer As New Person
Customer.Age = 25
Customer.IsMale = "Yes"

PeopleCollectio n.Add(Customer)

Dim y As New Person
y.Age = 25
Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
returns -1, meaning it didn't match anything
End Sub

Public Class Person
Private _IsMale As String
Private _age As Integer
Public Overloads Overrides Function equals(ByVal obj As Object) As Boolean
If obj Is Nothing Then Return False
If Me.GetType Is obj.GetType Then
Return Me.Age = CType(obj, Person).Age
End If
End Function
Public Property IsMale() As String
Get
Return _IsMale
End Get
Set(ByVal Value As String)
_IsMale = Value
End Set
End Property
Public Property Age() As Integer
Get
Return _age
End Get
Set(ByVal Value As Integer)
_age = Value
End Set
End Property
End Class

In this example I wanted to get the instance of the PERSON whose age is 25.
If I put a breakpoint in my overloads overrides equals method, it never
breaks. My EQUALS method is not being called.

Can anybody explain what is going on, and how I can get my indexof to do
what I need it to do?

Thanks, John
Nov 21 '05 #1
18 4763

JohnR wrote:
From reading the documentation, this should be a relatively easy thing. I have an arraylist of custom class instances which I want to search with an"indexof" where I'm passing an instance if the class where only the "searched" property has a value. I expected to get the index into the arraylist where I could then get the entire class instance. However, the 'indexof' is never calling my overloaded, overrides Equals method. Here is the code snippet:

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load

Dim PeopleCollectio n As New ArrayList

Dim Customer As New Person
Customer.Age = 25
Customer.IsMale = "Yes"

PeopleCollectio n.Add(Customer)

Dim y As New Person
y.Age = 25
Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
returns -1, meaning it didn't match anything
End Sub

Public Class Person
Private _IsMale As String
Private _age As Integer
Public Overloads Overrides Function equals(ByVal obj As Object) As Boolean If obj Is Nothing Then Return False
If Me.GetType Is obj.GetType Then
Return Me.Age = CType(obj, Person).Age
End If
End Function [snip]
In this example I wanted to get the instance of the PERSON whose age is 25. If I put a breakpoint in my overloads overrides equals method, it never breaks. My EQUALS method is not being called.

Can anybody explain what is going on, and how I can get my indexof to do what I need it to do?


This is technically a feature not a bug (doesn't help I know), as the
behaviour is as documented. In the docs for ArrayList.Index Of, you will
see it says:
Remarks
....
This method determines equality by calling Object.Equals.


which is why your class's Equals method is not being called. To get the
behaviour you want you have a number of choices which include these as
I think the most obvious two:

- Implement a strongly-typed ArrayList for storing solely Person
objects, that uses Person.Equals when doing an IndexOf operation;

- Use a different collection class, one that explicitly supports the
use of overriden Equals operators. For example, a Hashtable uses the
Equals implementation of the key objects, rather than always using
Object.Equals

If you need wither or both of these options explained more, feel free
to ask :)

--
Larry Lard
Replies to group please

Nov 21 '05 #2
Hi Larry,
- Implement a strongly-typed ArrayList for storing solely Person objects, that uses Person.Equals when doing an IndexOf operation;

I'm not exactly sure what you mean...

Every entry into the arraylist was of type PERSON. But, still, the indexof
didn't call the object.equals in the Person class. I'm guessing that it is
calling a object.equals method that is in the ArrayList class, so I tried
to create a new class ARRAYLISTPERSON which inherits from arraylist. I then
put the overrides overloads function equals(byval obj as object) as boolean
in the arraylistperson class def'n and stored my PERSON instances in this
class rather than the regular arraylist class. Unfortunately, when the
indexof method was called, my Equals function was not called, so I'm still
at a loss.

Do you have a small code example of how to override the Object.equals
method of an arraylist.index of?

Thanks, John
"Larry Lard" <la*******@hotm ail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .
JohnR wrote:
From reading the documentation, this should be a relatively easy

thing. I
have an arraylist of custom class instances which I want to search

with
an"indexof" where I'm passing an instance if the class where only the

"searched" property has a value. I expected to get the index into

the
arraylist where I could then get the entire class instance.

However, the
'indexof' is never calling my overloaded, overrides Equals method.

Here is
the code snippet:

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load

Dim PeopleCollectio n As New ArrayList

Dim Customer As New Person
Customer.Age = 25
Customer.IsMale = "Yes"

PeopleCollectio n.Add(Customer)

Dim y As New Person
y.Age = 25
Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
returns -1, meaning it didn't match anything
End Sub

Public Class Person
Private _IsMale As String
Private _age As Integer
Public Overloads Overrides Function equals(ByVal obj As Object) As

Boolean
If obj Is Nothing Then Return False
If Me.GetType Is obj.GetType Then
Return Me.Age = CType(obj, Person).Age
End If
End Function

[snip]

In this example I wanted to get the instance of the PERSON whose age

is 25.
If I put a breakpoint in my overloads overrides equals method, it

never
breaks. My EQUALS method is not being called.

Can anybody explain what is going on, and how I can get my indexof to

do
what I need it to do?


This is technically a feature not a bug (doesn't help I know), as the
behaviour is as documented. In the docs for ArrayList.Index Of, you will
see it says:
Remarks
...
This method determines equality by calling Object.Equals.


which is why your class's Equals method is not being called. To get the
behaviour you want you have a number of choices which include these as
I think the most obvious two:

- Implement a strongly-typed ArrayList for storing solely Person
objects, that uses Person.Equals when doing an IndexOf operation;

- Use a different collection class, one that explicitly supports the
use of overriden Equals operators. For example, a Hashtable uses the
Equals implementation of the key objects, rather than always using
Object.Equals

If you need wither or both of these options explained more, feel free
to ask :)

--
Larry Lard
Replies to group please

Nov 21 '05 #3

JohnR wrote:
Hi Larry,
> - Implement a strongly-typed ArrayList for storing solely
Person
> objects, that uses Person.Equals when doing an
IndexOf operation;

I'm not exactly sure what you mean...

Every entry into the arraylist was of type PERSON. But, still, the indexof didn't call the object.equals in the Person class. I'm guessing that it is calling a object.equals method that is in the ArrayList class,
An ArrayList will *always* use Object.Equals (the Equals method defined
in the base class Object) when checking for equality in its IndexOf
method. That is just the way ArrayList is implemented.

so I tried
to create a new class ARRAYLISTPERSON which inherits from arraylist. I then put the overrides overloads function equals(byval obj as object) as boolean in the arraylistperson class def'n and stored my PERSON instances in this class rather than the regular arraylist class. Unfortunately, when the indexof method was called, my Equals function was not called, so I'm still at a loss.
Supplying a new Equals method, wherever you do it, won't change
ArrayList's behaviour - it will always use Object.Equals.

Do you have a small code example of how to override the Object.equals method of an arraylist.index of?
What you need to change the behaviour of is the *IndexOf* method. Here
is the general idea:

Public Class ArrayListOfPers on
Inherits ArrayList

Public Shadows Function IndexOf(ByVal p As Person) As Integer
Dim iterp As Person
Dim i As Integer

For i = 0 To Me.Count - 1
iterp = DirectCast(Me(i ), Person)
If p.Equals(iterp) Then Return i
Next

Return -1
End Function
End Class

Usage example:

Dim al As ArrayList = New ArrayList

al.Add(New Person(10))
al.Add(New Person(5))

MsgBox(al.Index Of(New Person(5)))
'this will show -1, because ArrayList uses Object.Equals to
compare
'while performing the IndexOf method
'and Object.Equals requires reference equivalence

Dim alp As ArrayListOfPers on = New ArrayListOfPers on

alp.Add(New Person(10))
alp.Add(New Person(5))

MsgBox(alp.Inde xOf(New Person(5)))
'this will return 1, because ArrayListOfPers on uses
Person.Equals
'while performing IndexOf(As Person)
**** PLEASE NOTE **** that this lacks robustness in a number of ways,
and this is *not* how I would suggest implementing a strongly-typed
collection in anything larger than a toy (ie personal-use only)
application. The main problems are that: There is nothing to stop a
careless client of ArrayListOfPers on adding a non-Person; the Item()
property is still returned As Object so must be casted to Person; an
ArrayListOfPers on can be casted down to ArrayList and lose all its
custom behaviour. To reiterate, DON'T do custom collections in this way
in seroius apps! This is just an example! You can find many posts on
the correct ways to implement custom collections here in this group. Or
start a new thread and ask, as that is a separate topic :)

Thanks, John
"Larry Lard" <la*******@hotm ail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .

JohnR wrote:
From reading the documentation, this should be a relatively easy

thing. I
have an arraylist of custom class instances which I want to search

with
an"indexof" where I'm passing an instance if the class where only the
"searched" property has a value. I expected to get the index into

the
arraylist where I could then get the entire class instance.

However, the
'indexof' is never calling my overloaded, overrides Equals method.

Here is
the code snippet:

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load

Dim PeopleCollectio n As New ArrayList

Dim Customer As New Person
Customer.Age = 25
Customer.IsMale = "Yes"

PeopleCollectio n.Add(Customer)

Dim y As New Person
y.Age = 25
Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this
always returns -1, meaning it didn't match anything
End Sub

Public Class Person
Private _IsMale As String
Private _age As Integer
Public Overloads Overrides Function equals(ByVal obj As Object) As

Boolean
If obj Is Nothing Then Return False
If Me.GetType Is obj.GetType Then
Return Me.Age = CType(obj, Person).Age
End If
End Function

[snip]

In this example I wanted to get the instance of the PERSON whose

age is 25.
If I put a breakpoint in my overloads overrides equals method, it

never
breaks. My EQUALS method is not being called.

Can anybody explain what is going on, and how I can get my indexof
to do
what I need it to do?


This is technically a feature not a bug (doesn't help I know), as the behaviour is as documented. In the docs for ArrayList.Index Of, you will see it says:

Remarks
...
This method determines equality by calling Object.Equals.


which is why your class's Equals method is not being called. To get the behaviour you want you have a number of choices which include these as I think the most obvious two:

- Implement a strongly-typed ArrayList for storing solely Person
objects, that uses Person.Equals when doing an IndexOf operation;

- Use a different collection class, one that explicitly supports the use of overriden Equals operators. For example, a Hashtable uses the Equals implementation of the key objects, rather than always using
Object.Equals

If you need wither or both of these options explained more, feel free to ask :)

--
Larry Lard
Replies to group please


Nov 21 '05 #4
Hi Larry,

thanks for the quick reply. You have confirmed my idea of what needs to
be done... I have created my own custom arraylist as you suggested, and
created a few 'wrapper' functions to store/access/search/retrieve items
stored in it regardless of class.

it is a shame, however, that the arraylist.index of class doesn't call the
overridden object.equals methods. Oh, well...

Regards,
John

"Larry Lard" <la*******@hotm ail.com> wrote in message
news:11******** **************@ z14g2000cwz.goo glegroups.com.. .

JohnR wrote:
Hi Larry,
> - Implement a strongly-typed ArrayList for storing solely
Person
> objects, that uses Person.Equals when doing an

IndexOf
operation;

I'm not exactly sure what you mean...

Every entry into the arraylist was of type PERSON. But, still, the

indexof
didn't call the object.equals in the Person class. I'm guessing that

it is
calling a object.equals method that is in the ArrayList class,


An ArrayList will *always* use Object.Equals (the Equals method defined
in the base class Object) when checking for equality in its IndexOf
method. That is just the way ArrayList is implemented.

so I tried
to create a new class ARRAYLISTPERSON which inherits from arraylist.

I then
put the overrides overloads function equals(byval obj as object) as

boolean
in the arraylistperson class def'n and stored my PERSON instances in

this
class rather than the regular arraylist class. Unfortunately, when

the
indexof method was called, my Equals function was not called, so I'm

still
at a loss.


Supplying a new Equals method, wherever you do it, won't change
ArrayList's behaviour - it will always use Object.Equals.

Do you have a small code example of how to override the

Object.equals
method of an arraylist.index of?


What you need to change the behaviour of is the *IndexOf* method. Here
is the general idea:

Public Class ArrayListOfPers on
Inherits ArrayList

Public Shadows Function IndexOf(ByVal p As Person) As Integer
Dim iterp As Person
Dim i As Integer

For i = 0 To Me.Count - 1
iterp = DirectCast(Me(i ), Person)
If p.Equals(iterp) Then Return i
Next

Return -1
End Function
End Class

Usage example:

Dim al As ArrayList = New ArrayList

al.Add(New Person(10))
al.Add(New Person(5))

MsgBox(al.Index Of(New Person(5)))
'this will show -1, because ArrayList uses Object.Equals to
compare
'while performing the IndexOf method
'and Object.Equals requires reference equivalence

Dim alp As ArrayListOfPers on = New ArrayListOfPers on

alp.Add(New Person(10))
alp.Add(New Person(5))

MsgBox(alp.Inde xOf(New Person(5)))
'this will return 1, because ArrayListOfPers on uses
Person.Equals
'while performing IndexOf(As Person)
**** PLEASE NOTE **** that this lacks robustness in a number of ways,
and this is *not* how I would suggest implementing a strongly-typed
collection in anything larger than a toy (ie personal-use only)
application. The main problems are that: There is nothing to stop a
careless client of ArrayListOfPers on adding a non-Person; the Item()
property is still returned As Object so must be casted to Person; an
ArrayListOfPers on can be casted down to ArrayList and lose all its
custom behaviour. To reiterate, DON'T do custom collections in this way
in seroius apps! This is just an example! You can find many posts on
the correct ways to implement custom collections here in this group. Or
start a new thread and ask, as that is a separate topic :)

Thanks, John
"Larry Lard" <la*******@hotm ail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .
>
> JohnR wrote:
>> From reading the documentation, this should be a relatively easy
> thing. I
>> have an arraylist of custom class instances which I want to search
> with
>> an"indexof" where I'm passing an instance if the class where only

the >
>> "searched" property has a value. I expected to get the index into
> the
>> arraylist where I could then get the entire class instance.
> However, the
>> 'indexof' is never calling my overloaded, overrides Equals method.
> Here is
>> the code snippet:
>>
>> Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
>> System.EventArg s) Handles MyBase.Load
>>
>> Dim PeopleCollectio n As New ArrayList
>>
>> Dim Customer As New Person
>> Customer.Age = 25
>> Customer.IsMale = "Yes"
>>
>> PeopleCollectio n.Add(Customer)
>>
>> Dim y As New Person
>> y.Age = 25
>> Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always >> returns -1, meaning it didn't match anything
>> End Sub
>>
>> Public Class Person
>> Private _IsMale As String
>> Private _age As Integer
>> Public Overloads Overrides Function equals(ByVal obj As Object) As
> Boolean
>> If obj Is Nothing Then Return False
>> If Me.GetType Is obj.GetType Then
>> Return Me.Age = CType(obj, Person).Age
>> End If
>> End Function
> [snip]
>>
>> In this example I wanted to get the instance of the PERSON whose age > is 25.
>> If I put a breakpoint in my overloads overrides equals method, it
> never
>> breaks. My EQUALS method is not being called.
>>
>> Can anybody explain what is going on, and how I can get my indexof to > do
>> what I need it to do?
>
> This is technically a feature not a bug (doesn't help I know), as the > behaviour is as documented. In the docs for ArrayList.Index Of, you will > see it says:
>
>>>
> Remarks
> ...
> This method determines equality by calling Object.Equals.
>>>
>
> which is why your class's Equals method is not being called. To get the > behaviour you want you have a number of choices which include these as > I think the most obvious two:
>
> - Implement a strongly-typed ArrayList for storing solely Person
> objects, that uses Person.Equals when doing an IndexOf operation;
>
> - Use a different collection class, one that explicitly supports the > use of overriden Equals operators. For example, a Hashtable uses the > Equals implementation of the key objects, rather than always using
> Object.Equals
>
> If you need wither or both of these options explained more, feel free > to ask :)
>
> --
> Larry Lard
> Replies to group please
>

Nov 21 '05 #5
John,
Your code works as expected! As Larry pointed out, ArrayList.Index Of uses
Object.Equals to match the items. Object.Equals is an overridable method, so
it behaves polymorphically across any type that overrides it. Your Person
type overrides Object.Equals. So ArrayList.Index Of will call Person.Equals.

Trying your code as posted returns 0 in VB.NET 2003!

To see that Person.Equals is actually getting called, simply place a
breakpoint on the Person.Equals method before calling
PeopleCollectio n.IndexOf.

Hope this helps
Jay
"JohnR" <Jo******@hotma il.com> wrote in message
news:HRkbe.5251 $WX.1041@trndny 01...
| From reading the documentation, this should be a relatively easy thing.
I
| have an arraylist of custom class instances which I want to search with
| an"indexof" where I'm passing an instance if the class where only the
| "searched" property has a value. I expected to get the index into the
| arraylist where I could then get the entire class instance. However, the
| 'indexof' is never calling my overloaded, overrides Equals method. Here
is
| the code snippet:
|
| Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
| System.EventArg s) Handles MyBase.Load
|
| Dim PeopleCollectio n As New ArrayList
|
| Dim Customer As New Person
| Customer.Age = 25
| Customer.IsMale = "Yes"
|
| PeopleCollectio n.Add(Customer)
|
| Dim y As New Person
| y.Age = 25
| Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
| returns -1, meaning it didn't match anything
| End Sub
|
| Public Class Person
| Private _IsMale As String
| Private _age As Integer
| Public Overloads Overrides Function equals(ByVal obj As Object) As Boolean
| If obj Is Nothing Then Return False
| If Me.GetType Is obj.GetType Then
| Return Me.Age = CType(obj, Person).Age
| End If
| End Function
| Public Property IsMale() As String
| Get
| Return _IsMale
| End Get
| Set(ByVal Value As String)
| _IsMale = Value
| End Set
| End Property
| Public Property Age() As Integer
| Get
| Return _age
| End Get
| Set(ByVal Value As Integer)
| _age = Value
| End Set
| End Property
| End Class
|
| In this example I wanted to get the instance of the PERSON whose age is
25.
| If I put a breakpoint in my overloads overrides equals method, it never
| breaks. My EQUALS method is not being called.
|
| Can anybody explain what is going on, and how I can get my indexof to do
| what I need it to do?
|
| Thanks, John
|
|
Nov 21 '05 #6
Larry,
| >>
| Remarks
| ...
| This method determines equality by calling Object.Equals.
| >>
|
| which is why your class's Equals method is not being called. To get the
| behaviour you want you have a number of choices which include these as
Err! Object.Equals is overridable, John overrode it. Overridable means the
method behaves polymorphically .

When ArrayList.Index Of calls Object.Equals, because John's Person.Equals
overrides it, Person.Equals will actually be called!

Using Shadows is anti-polymorphic. When ArrayList.Index Of calls
Object.Equals, if Person shadows Equals, then Object.Equals will be called &
not Person.Equals. Rarely do you want to use Shadows as they are
anti-polymorphic!

John's code as posted works as expected, I suspect there is another problem
going on.

Hope this helps
Jay


"Larry Lard" <la*******@hotm ail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .
|
| JohnR wrote:
| > From reading the documentation, this should be a relatively easy
| thing. I
| > have an arraylist of custom class instances which I want to search
| with
| > an"indexof" where I'm passing an instance if the class where only the
|
| > "searched" property has a value. I expected to get the index into
| the
| > arraylist where I could then get the entire class instance.
| However, the
| > 'indexof' is never calling my overloaded, overrides Equals method.
| Here is
| > the code snippet:
| >
| > Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
| > System.EventArg s) Handles MyBase.Load
| >
| > Dim PeopleCollectio n As New ArrayList
| >
| > Dim Customer As New Person
| > Customer.Age = 25
| > Customer.IsMale = "Yes"
| >
| > PeopleCollectio n.Add(Customer)
| >
| > Dim y As New Person
| > y.Age = 25
| > Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
| > returns -1, meaning it didn't match anything
| > End Sub
| >
| > Public Class Person
| > Private _IsMale As String
| > Private _age As Integer
| > Public Overloads Overrides Function equals(ByVal obj As Object) As
| Boolean
| > If obj Is Nothing Then Return False
| > If Me.GetType Is obj.GetType Then
| > Return Me.Age = CType(obj, Person).Age
| > End If
| > End Function
| [snip]
| >
| > In this example I wanted to get the instance of the PERSON whose age
| is 25.
| > If I put a breakpoint in my overloads overrides equals method, it
| never
| > breaks. My EQUALS method is not being called.
| >
| > Can anybody explain what is going on, and how I can get my indexof to
| do
| > what I need it to do?
|
| This is technically a feature not a bug (doesn't help I know), as the
| behaviour is as documented. In the docs for ArrayList.Index Of, you will
| see it says:
|
| >>
| Remarks
| ...
| This method determines equality by calling Object.Equals.
| >>
|
| which is why your class's Equals method is not being called. To get the
| behaviour you want you have a number of choices which include these as
| I think the most obvious two:
|
| - Implement a strongly-typed ArrayList for storing solely Person
| objects, that uses Person.Equals when doing an IndexOf operation;
|
| - Use a different collection class, one that explicitly supports the
| use of overriden Equals operators. For example, a Hashtable uses the
| Equals implementation of the key objects, rather than always using
| Object.Equals
|
| If you need wither or both of these options explained more, feel free
| to ask :)
|
| --
| Larry Lard
| Replies to group please
|
Nov 21 '05 #7

Jay B. Harlow [MVP - Outlook] wrote:
Larry,
| >>
| Remarks
| ...
| This method determines equality by calling Object.Equals.
| >>
|
| which is why your class's Equals method is not being called. To get the | behaviour you want you have a number of choices which include these as Err! Object.Equals is overridable, John overrode it. Overridable means the method behaves polymorphically .

When ArrayList.Index Of calls Object.Equals, because John's Person.Equals overrides it, Person.Equals will actually be called!

Using Shadows is anti-polymorphic. When ArrayList.Index Of calls
Object.Equals, if Person shadows Equals, then Object.Equals will be called & not Person.Equals. Rarely do you want to use Shadows as they are
anti-polymorphic!

John's code as posted works as expected, I suspect there is another problem going on.


So it does. Guess I should have checked that before going off on one,
to avoid looking silly now. Oh well.

--
Larry Lard
Replies to group please

Nov 21 '05 #8
In article <HRkbe.5251$WX. 1041@trndny01>, JohnR wrote:
From reading the documentation, this should be a relatively easy thing. I
have an arraylist of custom class instances which I want to search with
an"indexof" where I'm passing an instance if the class where only the
"searched" property has a value. I expected to get the index into the
arraylist where I could then get the entire class instance. However, the
'indexof' is never calling my overloaded, overrides Equals method. Here is
the code snippet:

Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load

Dim PeopleCollectio n As New ArrayList

Dim Customer As New Person
Customer.Age = 25
Customer.IsMale = "Yes"

PeopleCollectio n.Add(Customer)

Dim y As New Person
y.Age = 25
Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
returns -1, meaning it didn't match anything
End Sub

Public Class Person
Private _IsMale As String
Private _age As Integer
Public Overloads Overrides Function equals(ByVal obj As Object) As Boolean
If obj Is Nothing Then Return False
If Me.GetType Is obj.GetType Then
Return Me.Age = CType(obj, Person).Age
End If
End Function
Public Property IsMale() As String
Get
Return _IsMale
End Get
Set(ByVal Value As String)
_IsMale = Value
End Set
End Property
Public Property Age() As Integer
Get
Return _age
End Get
Set(ByVal Value As Integer)
_age = Value
End Set
End Property
End Class

In this example I wanted to get the instance of the PERSON whose age is 25.
If I put a breakpoint in my overloads overrides equals method, it never
breaks. My EQUALS method is not being called.

Can anybody explain what is going on, and how I can get my indexof to do
what I need it to do?

Thanks, John


IMHO, this is a bug... The problem is that it seems that the arraylist
Index of operator does something like the following (obviously aircode):

For Each obj As Object in List
value.Equals (obj)
Next

Which is backwards from what you would expect:

For Each obj As Object in List
obj.Equals (value)
Next

So, to get around this you need create a custom collection class that
overrides IndexOf... Here is my C# implementation of a class I did:

public int IndexOf(string value)
{
int index = -1;

// HACK: Get around strange arraylist.index of method implementation. ..
for (int i = 0; i < this.InnerList. Count; i++)
{
if (this.InnerList[i].Equals(value))
{
index = i;
break;
}
}

return index;
}

The funny thing is that Mono did it the right way... But, broke it to
be like .NET in response to a post I made on the mono mailing list :)

--
Tom Shelton [MVP]
Nov 21 '05 #9
Tom,
| IMHO, this is a bug... The problem is that it seems that the arraylist
| Index of operator does something like the following (obviously aircode):

I don't see there is a Bug in John's code. If you try his code it works as
expected in VS.NET 2003 (.NET 1.1)!
| For Each obj As Object in List
| value.Equals (obj)
| Next
|
| Which is backwards from what you would expect:
|
| For Each obj As Object in List
| obj.Equals (value)
| Next

Object.Equals is defined such that "if x.Equals(y) return the same value as
y.Equals(x)" so I don't really see a problem or bug in your sample either!

http://msdn.microsoft.com/library/de...ualstopic1.asp

Hope this helps
Jay


"Tom Shelton" <to*@YOUKNOWTHE DRILLmtogden.co m> wrote in message
news:uz******** ******@TK2MSFTN GP14.phx.gbl...
| In article <HRkbe.5251$WX. 1041@trndny01>, JohnR wrote:
| > From reading the documentation, this should be a relatively easy thing.
I
| > have an arraylist of custom class instances which I want to search with
| > an"indexof" where I'm passing an instance if the class where only the
| > "searched" property has a value. I expected to get the index into the
| > arraylist where I could then get the entire class instance. However,
the
| > 'indexof' is never calling my overloaded, overrides Equals method. Here
is
| > the code snippet:
| >
| > Private Sub Form1_Load(ByVa l sender As System.Object, ByVal e As
| > System.EventArg s) Handles MyBase.Load
| >
| > Dim PeopleCollectio n As New ArrayList
| >
| > Dim Customer As New Person
| > Customer.Age = 25
| > Customer.IsMale = "Yes"
| >
| > PeopleCollectio n.Add(Customer)
| >
| > Dim y As New Person
| > y.Age = 25
| > Dim x As Integer = PeopleCollectio n.IndexOf(y) 'this always
| > returns -1, meaning it didn't match anything
| > End Sub
| >
| > Public Class Person
| > Private _IsMale As String
| > Private _age As Integer
| > Public Overloads Overrides Function equals(ByVal obj As Object) As
Boolean
| > If obj Is Nothing Then Return False
| > If Me.GetType Is obj.GetType Then
| > Return Me.Age = CType(obj, Person).Age
| > End If
| > End Function
| > Public Property IsMale() As String
| > Get
| > Return _IsMale
| > End Get
| > Set(ByVal Value As String)
| > _IsMale = Value
| > End Set
| > End Property
| > Public Property Age() As Integer
| > Get
| > Return _age
| > End Get
| > Set(ByVal Value As Integer)
| > _age = Value
| > End Set
| > End Property
| > End Class
| >
| > In this example I wanted to get the instance of the PERSON whose age is
25.
| > If I put a breakpoint in my overloads overrides equals method, it never
| > breaks. My EQUALS method is not being called.
| >
| > Can anybody explain what is going on, and how I can get my indexof to do
| > what I need it to do?
| >
| > Thanks, John
| >
| >
|
| IMHO, this is a bug... The problem is that it seems that the arraylist
| Index of operator does something like the following (obviously aircode):
|
| For Each obj As Object in List
| value.Equals (obj)
| Next
|
| Which is backwards from what you would expect:
|
| For Each obj As Object in List
| obj.Equals (value)
| Next
|
| So, to get around this you need create a custom collection class that
| overrides IndexOf... Here is my C# implementation of a class I did:
|
| public int IndexOf(string value)
| {
| int index = -1;
|
| // HACK: Get around strange arraylist.index of method implementation. ..
| for (int i = 0; i < this.InnerList. Count; i++)
| {
| if (this.InnerList[i].Equals(value))
| {
| index = i;
| break;
| }
| }
|
| return index;
| }
|
| The funny thing is that Mono did it the right way... But, broke it to
| be like .NET in response to a post I made on the mono mailing list :)
|
| --
| Tom Shelton [MVP]
Nov 21 '05 #10

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