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Question about events and object arrays

Hi,

Finally figured events and delegates whew! Thanks to the people in this
community that helped me out.

So now I have a class that raises an event.

Now if I instantiate an object array of that class, and the event fires, is
there any way of getting the array index of the object that raised that event?

Thanks in advance.

Pete.
Nov 16 '05 #1
  • viewed: 1529
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9 Replies
Peter,

Yes, there is. Since you would be using one event handler for all the
items in the array, you can cycle through the array and then compare object
refrences with the sender of the object (this is assuming you followed the
pattern for event handlers, where the first parameter is the object that
fired the event, the second is of type EventArgs or derived from EventArgs.
Don't worry, I'll wait while you make the changes. Done? Ok =) ). Once
you do that, you will have your index.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com
"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:8D**********************************@microsof t.com...
Hi,

Finally figured events and delegates whew! Thanks to the people in this
community that helped me out.

So now I have a class that raises an event.

Now if I instantiate an object array of that class, and the event fires,
is
there any way of getting the array index of the object that raised that
event?

Thanks in advance.

Pete.

Nov 16 '05 #2
Nicholas,

I think you were the one to point me to the paradigm of event handlers in
the first place. I did that.
My event handler now takes arguments of "sender" type object and
"derivedEventArgs" which derives from System.EventArgs.

What I was looking for is how to compare object references or cycle through
that array. Do you mean using a for loop?

Thanks,

Pete.

"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, there is. Since you would be using one event handler for all the
items in the array, you can cycle through the array and then compare object
refrences with the sender of the object (this is assuming you followed the
pattern for event handlers, where the first parameter is the object that
fired the event, the second is of type EventArgs or derived from EventArgs.
Don't worry, I'll wait while you make the changes. Done? Ok =) ). Once
you do that, you will have your index.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com
"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:8D**********************************@microsof t.com...
Hi,

Finally figured events and delegates whew! Thanks to the people in this
community that helped me out.

So now I have a class that raises an event.

Now if I instantiate an object array of that class, and the event fires,
is
there any way of getting the array index of the object that raised that
event?

Thanks in advance.

Pete.


Nov 16 '05 #3
Peter,

Yes, I do. I assume the event handler has access to the original object
array. In this case, enumerate through each of these elements in the array,
comparing the object reference (use the static ReferenceEquals method on
object to be sure) to the sender.

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:54**********************************@microsof t.com...
Nicholas,

I think you were the one to point me to the paradigm of event handlers in
the first place. I did that.
My event handler now takes arguments of "sender" type object and
"derivedEventArgs" which derives from System.EventArgs.

What I was looking for is how to compare object references or cycle
through
that array. Do you mean using a for loop?

Thanks,

Pete.

"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, there is. Since you would be using one event handler for all
the
items in the array, you can cycle through the array and then compare
object
refrences with the sender of the object (this is assuming you followed
the
pattern for event handlers, where the first parameter is the object that
fired the event, the second is of type EventArgs or derived from
EventArgs.
Don't worry, I'll wait while you make the changes. Done? Ok =) ). Once
you do that, you will have your index.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com
"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
message
news:8D**********************************@microsof t.com...
> Hi,
>
> Finally figured events and delegates whew! Thanks to the people in this
> community that helped me out.
>
> So now I have a class that raises an event.
>
> Now if I instantiate an object array of that class, and the event
> fires,
> is
> there any way of getting the array index of the object that raised that
> event?
>
> Thanks in advance.
>
> Pete.


Nov 16 '05 #4
Nicholas,

Thanks for the clarification.

However, is there another way of doing that? The reason I ask is because if
you have an array of a 100,000 objects theoretically, then looping through
the entire array would be expensive. Compund it with the fact that the events
are happening fairly quickly and in repeated succession.

Is there a way of passing a handle of the specific array object to the class
that raises the event handler, and return that handle with the event data?

Thank you,

Pete.
"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, I do. I assume the event handler has access to the original object
array. In this case, enumerate through each of these elements in the array,
comparing the object reference (use the static ReferenceEquals method on
object to be sure) to the sender.

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:54**********************************@microsof t.com...
Nicholas,

I think you were the one to point me to the paradigm of event handlers in
the first place. I did that.
My event handler now takes arguments of "sender" type object and
"derivedEventArgs" which derives from System.EventArgs.

What I was looking for is how to compare object references or cycle
through
that array. Do you mean using a for loop?

Thanks,

Pete.

"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, there is. Since you would be using one event handler for all
the
items in the array, you can cycle through the array and then compare
object
refrences with the sender of the object (this is assuming you followed
the
pattern for event handlers, where the first parameter is the object that
fired the event, the second is of type EventArgs or derived from
EventArgs.
Don't worry, I'll wait while you make the changes. Done? Ok =) ). Once
you do that, you will have your index.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com
"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
message
news:8D**********************************@microsof t.com...
> Hi,
>
> Finally figured events and delegates whew! Thanks to the people in this
> community that helped me out.
>
> So now I have a class that raises an event.
>
> Now if I instantiate an object array of that class, and the event
> fires,
> is
> there any way of getting the array index of the object that raised that
> event?
>
> Thanks in advance.
>
> Pete.


Nov 16 '05 #5
If you're using a plain ol' array, you can do this:

Control[] controlArray = ... ;
for (int i = 0; i < controlArray.Length && sender != controlArray[i];
i++)
{ }
if (i >= controlArray.Length)
{
i = -1;
}

i will then contain the index of the control in the array, or will be
-1 if the control was not found.

However, if you don't need the controls to be stored in any sort of
order, I would suggest a Hashtable instead. For each new control, add
it to the Hashtable:

Hashtable controls = new Hashtable();
Control aControl = new ... ;
controls[aControl] = aControl;

then you can find out if the control is in the Hashtable in one line of
code:

if (controls[sender] != null)
{
.... control has been found...
}

Of course, as I said, it all depends upon whether you need the controls
to be stored in order. (Event then, look into SortedList and other
aggregate structures to see if one offers all of the features you need.
There's more to life than arrays!)

Nov 16 '05 #6
If you're using a plain ol' array, you can do this:

Control[] controlArray = ... ;
for (int i = 0; i < controlArray.Length && sender != controlArray[i];
i++)
{ }
if (i >= controlArray.Length)
{
i = -1;
}

i will then contain the index of the control in the array, or will be
-1 if the control was not found.

However, if you don't need the controls to be stored in any sort of
order, I would suggest a Hashtable instead. For each new control, add
it to the Hashtable:

Hashtable controls = new Hashtable();
Control aControl = new ... ;
controls[aControl] = aControl;

then you can find out if the control is in the Hashtable in one line of
code:

if (controls[sender] != null)
{
.... control has been found...
}

Of course, as I said, it all depends upon whether you need the controls
to be stored in order. (Event then, look into SortedList and other
aggregate structures to see if one offers all of the features you need.
There's more to life than arrays!)

Nov 16 '05 #7
Hello Peter,

I'm not sure why you would need the array index of the item, since you already
have a reference to the object in question. But if you could change your
array to an arraylist then you could find the index by using the BinarySearch
method.

But again if you already have a reference to the object (through the sender
param of the even) why get the index?

-john
Hi,

Finally figured events and delegates whew! Thanks to the people in
this community that helped me out.

So now I have a class that raises an event.

Now if I instantiate an object array of that class, and the event
fires, is there any way of getting the array index of the object that
raised that event?

Thanks in advance.

Pete.

Nov 16 '05 #8
Peter,

In this situation, I would recommend that you give the object some sense
of the index that it is at. For example, when you assign it in an array,
you would assign a property indicating the index in the array it is at.

However, I can see where people would cringe at this.

You might want to consider having a wrapper for the array which exposes
the event. The EventArgs-derived class would have an index on it,
indicating the index of the item that fired the event, and the sender would
have the actual object.

I'm curious though, what do you need the index of the item in the array
for if you have the sender?
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:9F**********************************@microsof t.com...
Nicholas,

Thanks for the clarification.

However, is there another way of doing that? The reason I ask is because
if
you have an array of a 100,000 objects theoretically, then looping through
the entire array would be expensive. Compund it with the fact that the
events
are happening fairly quickly and in repeated succession.

Is there a way of passing a handle of the specific array object to the
class
that raises the event handler, and return that handle with the event data?

Thank you,

Pete.
"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, I do. I assume the event handler has access to the original
object
array. In this case, enumerate through each of these elements in the
array,
comparing the object reference (use the static ReferenceEquals method on
object to be sure) to the sender.

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
message
news:54**********************************@microsof t.com...
> Nicholas,
>
> I think you were the one to point me to the paradigm of event handlers
> in
> the first place. I did that.
> My event handler now takes arguments of "sender" type object and
> "derivedEventArgs" which derives from System.EventArgs.
>
> What I was looking for is how to compare object references or cycle
> through
> that array. Do you mean using a for loop?
>
> Thanks,
>
> Pete.
>
>
>
> "Nicholas Paldino [.NET/C# MVP]" wrote:
>
>> Peter,
>>
>> Yes, there is. Since you would be using one event handler for all
>> the
>> items in the array, you can cycle through the array and then compare
>> object
>> refrences with the sender of the object (this is assuming you followed
>> the
>> pattern for event handlers, where the first parameter is the object
>> that
>> fired the event, the second is of type EventArgs or derived from
>> EventArgs.
>> Don't worry, I'll wait while you make the changes. Done? Ok =) ).
>> Once
>> you do that, you will have your index.
>>
>> Hope this helps.
>>
>>
>> --
>> - Nicholas Paldino [.NET/C# MVP]
>> - mv*@spam.guard.caspershouse.com
>>
>>
>> "Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
>> message
>> news:8D**********************************@microsof t.com...
>> > Hi,
>> >
>> > Finally figured events and delegates whew! Thanks to the people in
>> > this
>> > community that helped me out.
>> >
>> > So now I have a class that raises an event.
>> >
>> > Now if I instantiate an object array of that class, and the event
>> > fires,
>> > is
>> > there any way of getting the array index of the object that raised
>> > that
>> > event?
>> >
>> > Thanks in advance.
>> >
>> > Pete.
>>
>>
>>


Nov 16 '05 #9
Nicholas,

Thank you for the info. The reason was that I was experimenting making as
dum linear data structure and thats why I needed the indices, but as Bruce
Wood suggested, I might be better off using the HashTable class.

I am new to C# and OOP and I am just getting my hands dirty, thats all.

Thanks,

Pete.

"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

In this situation, I would recommend that you give the object some sense
of the index that it is at. For example, when you assign it in an array,
you would assign a property indicating the index in the array it is at.

However, I can see where people would cringe at this.

You might want to consider having a wrapper for the array which exposes
the event. The EventArgs-derived class would have an index on it,
indicating the index of the item that fired the event, and the sender would
have the actual object.

I'm curious though, what do you need the index of the item in the array
for if you have the sender?
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in message
news:9F**********************************@microsof t.com...
Nicholas,

Thanks for the clarification.

However, is there another way of doing that? The reason I ask is because
if
you have an array of a 100,000 objects theoretically, then looping through
the entire array would be expensive. Compund it with the fact that the
events
are happening fairly quickly and in repeated succession.

Is there a way of passing a handle of the specific array object to the
class
that raises the event handler, and return that handle with the event data?

Thank you,

Pete.
"Nicholas Paldino [.NET/C# MVP]" wrote:
Peter,

Yes, I do. I assume the event handler has access to the original
object
array. In this case, enumerate through each of these elements in the
array,
comparing the object reference (use the static ReferenceEquals method on
object to be sure) to the sender.

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
message
news:54**********************************@microsof t.com...
> Nicholas,
>
> I think you were the one to point me to the paradigm of event handlers
> in
> the first place. I did that.
> My event handler now takes arguments of "sender" type object and
> "derivedEventArgs" which derives from System.EventArgs.
>
> What I was looking for is how to compare object references or cycle
> through
> that array. Do you mean using a for loop?
>
> Thanks,
>
> Pete.
>
>
>
> "Nicholas Paldino [.NET/C# MVP]" wrote:
>
>> Peter,
>>
>> Yes, there is. Since you would be using one event handler for all
>> the
>> items in the array, you can cycle through the array and then compare
>> object
>> refrences with the sender of the object (this is assuming you followed
>> the
>> pattern for event handlers, where the first parameter is the object
>> that
>> fired the event, the second is of type EventArgs or derived from
>> EventArgs.
>> Don't worry, I'll wait while you make the changes. Done? Ok =) ).
>> Once
>> you do that, you will have your index.
>>
>> Hope this helps.
>>
>>
>> --
>> - Nicholas Paldino [.NET/C# MVP]
>> - mv*@spam.guard.caspershouse.com
>>
>>
>> "Peter Krikelis" <Pe***********@discussions.microsoft.com> wrote in
>> message
>> news:8D**********************************@microsof t.com...
>> > Hi,
>> >
>> > Finally figured events and delegates whew! Thanks to the people in
>> > this
>> > community that helped me out.
>> >
>> > So now I have a class that raises an event.
>> >
>> > Now if I instantiate an object array of that class, and the event
>> > fires,
>> > is
>> > there any way of getting the array index of the object that raised
>> > that
>> > event?
>> >
>> > Thanks in advance.
>> >
>> > Pete.
>>
>>
>>


Nov 16 '05 #10

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