attribute variables and member variables in OBJETIVE-C

　　　

Property Variables @property and @synthesize can automatically generate access methods for a class member variable.

ReadWrite: This property is the default and will automatically generate accessors

Assign: This property is generally used to deal with the underlying types, such as int, float, and so on.

Copy: Specifies that a copy of the object (deep copy) should be used, and the previous value sends a release message.

Basically like retain, but without increasing the reference count, it is allocating a new piece of memory to place it.

Copy is to create a new object, retain is to create a pointer to reference the object Count plus 1. Copy

Create an object with an index count of 1. Then release the old object, copy is to create a new object,

Retain is to create a pointer that references an object plus 1.

ReadOnly: Only getter methods will be generated, not setter methods.

ReadWrite: Default property that will generate getter and setter methods with no extra parameters (setter has only one parameter)

Atomic: The default property for an object is that the Setter/getter generated method is an atomic operation. If multiple

When a thread calls the setter at the same time, one thread does not appear before the entire setter statement is executed, and the other

When a thread starts executing a setter, it is the same as the method ends with a lock.

Nonatomic: The atomicity of Setter/getter is not guaranteed, and data may be problematic in multithreaded situations.

nonatomic, non-atomic access, non-synchronous, multi-threaded concurrent access improves performance. First release the original

variable, and then the new variable retain then assigns the value;

　　A member variable is a private variable of the class that is visible only to that class.

attribute variables and member variables in OBJETIVE-C