ArrayList.Add - unexpected behavior

  • Thread starter Thread starter Adam
  • Start date Start date
A

Adam

Hi all,

The output of the code below is:
This is Message 2
This is Message 2

But I expected:
This is Message 1
This is Message 2

Can anyone help me understand what I am doing wrong? Thanks!


using System;
using System.Collections;

namespace test
{
public class Message
{
private string text;
public string Text
{
get{return text;}
set{text=value;}
}
}
class Class1
{
[STAThread]
static void Main(string[] args)
{
ArrayList Messagebox = new ArrayList();

Message oMessage=new Message();
oMessage.Text="This is Message 1";
Messagebox.Add(oMessage);
oMessage.Text="This is Message 2";
Messagebox.Add(oMessage);

Message mymess=(Message)Messagebox[0];
Console.WriteLine(mymess.Text);
Message mymess2=(Message)Messagebox[1];
Console.WriteLine(mymess.Text);
}
}
}
 
Correction, here's my code:

using System;
using System.Collections;

namespace test
{
public class Message
{
private string text;
public string Text
{
get{return text;}
set{text=value;}
}
}
class Class1
{
[STAThread]
static void Main(string[] args)
{
ArrayList Messagebox = new ArrayList();

Message oMessage=new Message();
oMessage.Text="This is Message 1";
Messagebox.Add(oMessage);
oMessage.Text="This is Message 2";
Messagebox.Add(oMessage);

Message mymess=(Message)Messagebox[0];
Console.WriteLine(mymess.Text);
mymess=(Message)Messagebox[1];
Console.WriteLine(mymess.Text);
}
}
}
 
Adam said:
Message oMessage=new Message();
oMessage.Text="This is Message 1";
Messagebox.Add(oMessage);
oMessage.Text="This is Message 2";
Messagebox.Add(oMessage);
Click to expand...

The problem is right here. Instead of creating a new instance and
setting its Text property for the second call to ArrayList.Add, you
modified the Text of the first instance and added it to your ArrayList
again.

So now you've got two references to a single Message object whose Text
property is set to "This is Message 2".

--
There are 10 kinds of people. Those who understand binary and those who
don't.

http://code.acadx.com
(Pull the pin to reply)
 
Thanks Frank for the information.

I may need to add hundreds of messages at a time into this ArrayList. Is
there an efficient way to add the messages to the ArrayList in series,
without having to do something like this:?

Message MessageA=new Message();
MessageA.Text="First message";
Messagebox.Add(MessageA);

Message MessageB=new Message();
MessageB.Text="Second message";
Messagebox.Add(MessageB);

Message MessageC=new Message();
MessageC.Text="Third message";
Messagebox.Add(MessageC);

Message MessageD=new Message();
MessageD.Text="Fourth message";
Messagebox.Add(MessageD);

etc. etc.

Thanks!



The reason I ask is that say I need to add 6 or 7 messages in a row into
 
Adam said:
Thanks Frank for the information.

I may need to add hundreds of messages at a time into this ArrayList. Is
there an efficient way to add the messages to the ArrayList in series,
without having to do something like this:?

Message MessageA=new Message();
MessageA.Text="First message";
Messagebox.Add(MessageA);
Click to expand...

How about defining a constructor for Message, and doing this?

Messagebox.Add(new Message("First message"))
Messagebox.Add(new Message("Second message"))

and so on...
 
Back
Top