i use xcode 9
NSMutableArray *Upcase_Keys = @[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"];
NSString *str = [Upcase_Keys objectAtIndex:0];
str = @"test";
[Upcase_Keys replaceObjectAtIndex:0 withObject:str];
Gets specific data for NSMutableArray
It transforms the value and overwrites the existing index.
However, this code causes a crash.
What did I do wrong?
NSMutableArray replaceObjectAtIndex Crash
So there should be an error in console. Console will help you 99% of the cases when there is a crash, read it!
It should be something like -[NSArrayI replaceObjectAtIndex:withObject:] unrecognized selector sent to instance. That's the important part of your error. NSArrayI meaning NSImmutableArray (NSArray in other words), which is not a NSMutableArray which points out that the issue is about the creation of Upcase_Keys.
Why then? Because @[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"]; that's a short hand syntax for NSArray, not NSMutableArray. So even if it's declared as a NSMutableArray, the object is in fact a NSArray.
In fact, if you'd listen to XCode, it should give you this warning:
Incompatible pointer types initializing
'NSMutableArray *'with an expression of type'NSArray *'
Which concords with everything said before.` Sometimes XCode may be wrong, but try to listen to it.
There are a few possibilities call:
NSMutableArray *Upcase_Keys = [NSMutableArray arrayWithArray:@[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"]];
NSMutableArray *Upcase_Keys = [[NSMutableArray alloc] initWithArray:@[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"]];
NSMutableArray *Upcase_Keys = [@[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"] mutableCopy];
And finally, a recommendation use camelcase:
Avoid naming your var with an uppercase. Use a lower case for the first letter. I'd say that after the _ is less problematic, but we tend in iOS to write instead.
Upcase_Keys => upcase_Keys => upcaseKeys
You have defined as immutable object, The syntax will assign NSArray reference not NSMutableArray. You can't update the NSArray.
Try like this,
NSMutableArray *Upcase_Keys = [NSMutableArray arrayWithArray:@[@"1",@"2",@"3",@"4,"@"5",@"6",@"7",@"8",@"9",@"0"]];
