Array items showing error in IOS - ios

Question

I have an array with some items to rotate the image view when button is clicked, now when I pass the array with getting current index it showing an error, I'm confused why I'm getting this.
My code is this:
- (IBAction)my:(id)sender {
NSString *cureentIndex=0;
NSArray *persons = [NSArray arrayWithObjects:#"M_PI",#" M_PI_4",#" M_PI_2",#"M_PI*2", nil];
NSArray *person = #[#"M_PI", #"M_PI_4", #"M_PI_2"];
_imageView.transform = CGAffineTransformMakeRotation(person[cureentIndex])
if currentIndex != persons.count-1 {
currentIndex = currentIndex + 1
}else {
// reset the current index back to zero
currentIndex = 0
}
}
The error is here:

Answer 1

You have declared cureentIndex as NSString *, so when you say person[cureentIndex] the compiler thinks that person must be a dictionary, since you are using the [] access with an object. This causes the error since person is actually an array and it cannot be indexed with a string.
I think you meant to declare cureentIndex as int, or perhaps you meant to say currentIndex?

Answer 2

There are a lot of issues, please try this
NSInteger currentIndex = 0;
NSArray<NSNumber *> *persons = #[#(M_PI), #(M_PI_4), #(M_PI_2)];
- (IBAction)my:(id)sender {
_imageView.transform = CGAffineTransformMakeRotation(persons[currentIndex].doubleValue)
currentIndex = (currentIndex + 1) % persons.count;
}

Answer 3

There are some errors:
The index must be an int
NSString *cureentIndex=0;
becomes
int currentIndex = 0;
and the array must be of double not string, CGAffineTransformMakeRotation requires a CGFloat that is a double
NSArray *person = #[#"M_PI", #"M_PI_4", #"M_PI_2"];
becomes
NSArray *person = #[[NSNumber numberWithDouble:M_PI], [NSNumber numberWithDouble:M_PI_4], [NSNumber numberWithDouble:M_PI_2]];
and
_imageView.transform = CGAffineTransformMakeRotation(person[cureentIndex])
becomes
_imageView.transform = CGAffineTransformMakeRotation([person[cureentIndex] doubleValue]);

Answer 4

I don't know why you set currentIndex's property to NSString, In fact we always set the XXXindex(current/last/next) to int or NSInteger property.
Another, the person is an array, it's key must be an int!, it's
value could be any object.
I fix your code to this:
NSInteger currentIndex = 0;
NSArray *person = #[#"M_PI", #"M_PI_4", #"M_PI_2"];
CGFloat rotate = [person[currentIndex] floatValue];
_imageView.transform = CGAffineTransformMakeRotation(rotate);
you will find it did't work well, the ratate will be 0! Because, the NSString's method floatValue or doubleValue can only change string(like: #"123" #"0.5") to a number, the string(like: #"M_PI") can't be change to a right number.
I fix your code to this again:
NSInteger currentIndex = 0;
CGFloat mPi = M_PI;
NSArray *person = #[#(mPi), #(mPi / 4.0), #(mPi / 2.0)];
CGFloat rotate = [person[currentIndex] floatValue];
_imageView.transform = CGAffineTransformMakeRotation(rotate);
The Code works well! This is because M_PI is A Macro, if you
write code #"M_PI", the system can't recognize its value 3.1415926. So
your must write M_PI instead of #"M_PI".
In fact, this problem's core is you need a number, so your array must include some numbers! Or some string just like number! :)