从JSON响应对象获取价值

Question

I am making a JSON request and want to get an int value from one of the fields.

{
"currentPage": 1,
"numberOfPages": 5,
"totalResults": 234,
"data": [],
"status": "success"
}

I want to get the value of numberOfPages. My code is as follows

_pages = [responseObject objectForKey:@"numberOfPages"];
_numberOfPages = (int)_pages;
NSLog(@"%d", _numberOfPages);

Instead of the value for numberOfPages, the NSLog is 150198512. Can somebody please explain why? Trying object at index 0 causes it to crash.

Answer 1

_pages should be an NSNumber in your definition. You can't cast that to get a primitive type, you have to request the primitive type. _numberOfPages should be an NSInteger (or perhaps NSUInteger ) and you should get the value with:

_numberOfPages = [_pages integerValue];

Aside: consider using self.pages and self.numberOfPages rather than accessing the instance variables directly (it could help you with maintenance in the future).

Using self.pages results in a call to the pages (or self.pages = xxx in a call to setPages:xxx ) method to get (or set) the content of the instance variable ( _pages ). So, if you have a custom implementation of that method it will be called and your custom logic will run. If you just use _pages then it won't be called and you will need to do a lot of editing later if you need to make a change.

Your best option is to use self.XXX = xxx whenever you want to update a property and XXX xxx = self.xxx when you want to use it.

This isn't a hard and fast rule. Interesting discussion here .