Setting a value in an array in obj-c

Question

I know this is a really simple thing in obj-c, but I can't seem to find anywhere (on here or google) how to do this. Basically I just want to replace one array value (the value is a NSString) with another, so something like this...

[sharedInstance.groundMap objectAtIndex:ii] = myImage;

But I get an error expression is not assignable. I also tried...

[[sharedInstance.groundMap objectAtIndex:ii] setValue:(NSString*) myImage];

But that gives an error too.

Really Phil, you couldn't find it anywhere? How about the NSMutableArray Class Reference? I don't understand why so many people look for answers on google or SO, you should go to the Apple docs first. — rdelmar
– rdelmar, Commented Oct 31, 2012 at 4:38

Sergey Kalinichenko · Accepted Answer · 2012-10-31 04:06:51Z

2

First, your array needs to be mutable (i.e. an instance of NSMutableArray, not simply NSArray). With NSMutableArray you can do this:

[sharedInstance.groundMap replaceObjectAtIndex:ii withObject:myImage];

If you have the latest Xcode, you can use the array[index] = value syntax as well.

answered Oct 31, 2012 at 4:06

Sergey Kalinichenko

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Comments

rmaddy · Accepted Answer · 2012-10-31 04:06:30Z

1

You need to be using an NSMutableArray to set a value. Use the replaceObjectAtIndex:withObject: method or use the new Objective-C syntax:

[sharedInstance.groundMap replaceObjecAtIndex:ii withObject:myImage];

or

sharedInstance.groundMap[ii] = myImage;

Neither works with NSArray. Only NSMutableArray.

answered Oct 31, 2012 at 4:06

rmaddy

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Comments

usergio2 · Accepted Answer · 2012-10-31 04:08:06Z

0

This is what you might want

[sharedInstance.groundMap replaceObjectAtIndex:11 withObject:[NSString stringWithFormat:@"test"]];

answered Oct 31, 2012 at 4:08

usergio2

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2 Comments

rmaddy Over a year ago

Why are you using stringWithFormat: for a string literal with no formatting?

usergio2 Over a year ago

it just part of the code i use before since your myImage is an NSString you can use it directly as @maddy and @dasblinkenlight suggested

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