IOS Variable vs Property

iosobjective cxcode

Just started diving into Objective-C and IOS development and was wondering when and the correct location I should be declaring variables/properties. The main piece of code i need explaining is below:

Why and when should i be declaring variables inside the interface statement and why do they have the same variable with _ and then the same one as a property. And then in the implementation they do @synthesize tableView = _tableView (I understand what synthesize does)

Thanks 🙂 

@interface ViewController : UIViewController <UITableViewDataSource, UITableViewDelegate> 
{
    UITableView *_tableView;
    UIActivityIndicatorView *_activityIndicatorView;
    NSArray *_movies;
}

@property (nonatomic, retain) UITableView *tableView;
@property (nonatomic, retain) UIActivityIndicatorView *activityIndicatorView;
@property (nonatomic, retain) NSArray *movies;

Best Answer

First of all, there is no need to declare the instance variables for properties as the statement 

@synthesize var = _iVar;

is actually generating an implicit variable named _iVar for you.

You would create properties when you want them to be accessible outside the class like

YourClass *obj = [[YourClass alloc] init];
obj.yourProperty = somevalue;

Properties also relieve you of writing your own getters & setters and take care of much of memory management themselves. Here is something you might wanna read plus other articles linked within the post.

http://cocoawithlove.com/2008/08/in-defense-of-objective-c-20-properties.html

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