Question

I’m new to Objective-C, so I may be phrasing this incorrectly.
I’ve created a Class “Message” and I instantiate it like this:

Message *newmsg=[[Message alloc]init];

When I access the contents of newmsg I do this (for example):

NSString *junk=((Message *)[globDat.allMsgs objectAtIndex:i]).text

I want to swap the contents of two instances. Especially because there are multiple items in the class.
For example the idea is this (pseudocode)

Message *TopMsg=[[Message alloc]init];
Message *BottomMsg=[[Message alloc]init];
Message *tmpmsg=[[Message alloc]init];
...
//enter values for TopMsg.xyz and BottomMsg.xyz
....
//swap
tmpmsg=TopMsg;
TopMsg=BottomMsg;
BottomMsg=tmpmsg;

EDIT: I left out the bit about using an array in a Singleton to hold multiple Message instances. You can kind of see it in the example about accessing the contents.

So just swapping pointers gives me an error: “Expression not assignable”

I’ve tried this (where allMsgs is the Array in the Singleton):

GlobalData *globDat=[GlobalData getSingleton];
Message *newmsg=[[Message alloc]init];
newmsg=[globDat.allMsgs objectAtIndex:0];
[globDat.allMsgs objectAtIndex:0]=[globDat.allMsgs objectAtIndex:1]; //<--ERROR

and this:

GlobalData *globDat=[GlobalData getSingleton];
Message *newmsg=[[Message alloc]init];
newmsg=[globDat.allMsgs objectAtIndex:0];
(Message *)[globDat.allMsgs objectAtIndex:0]=(Message *)[globDat.allMsgs objectAtIndex:1]; //<--ERROR

How can I do this?

Answer 1

The first thing you need to do is make sure your allMsgs property contains an instance of NSMutableArray. Then simply do this:

[globData.allMsgs exchangeObjectAtIndex:0 withObjectAtIndex:1];