What is the difference between strong and weak references?
The key difference between a strong and a weak or unowned reference is that a strong reference prevents the class instance it points to from being deallocated. In other words, weak and unowned references cannot prevent a class instance from being deallocated.
What is strong reference and weak reference in Objective-C?
Objective-C uses reference counting to manage the memory of its objects through the concept of object ownership. There are two types of object reference: Strong references, which keep an object “alive” in memory. Weak references, which have no effect on the lifetime of a referenced object.
What is the defining characteristic of a weak reference?
In computer programming, a weak reference is a reference that does not protect the referenced object from collection by a garbage collector, unlike a strong reference.
What does strong Mean Objective-C?
strong / retain : Declaring strong means that you want to “own” the object you are referencing. In Objective-C, an object is kept alive as long as it has at least one strong reference to it from another object. In non-ARC code strong is just a synonym for retain.
What is weak in Objective C?
weak specifies a reference that does not keep the referenced object alive. A weak reference is set to nil when there are no strong references to the object.
What is weak and unowned?
The main difference between weak and unowned is that weak is optional while unowned is non-optional. By declaring it weak you get to handle the case that it might be nil inside the closure at some point. If you try to access an unowned variable that happens to be nil, it will crash the whole program.
When should you use weak reference?
Use long weak references only when necessary as the state of the object is unpredictable after finalization. Avoid using weak references to small objects because the pointer itself may be as large or larger. Avoid using weak references as an automatic solution to memory management problems.
How does a weak reference work?
A weakly referenced object is cleared by the Garbage Collector when it’s weakly reachable. Weak reachability means that an object has neither strong nor soft references pointing to it. The object can be reached only by traversing a weak reference.
What’s the difference between strong and weak reference type?
The fundamental difference between weak and strong reference type is decided by RETURN clause of cursor type declaration. If RETURN type clause is missing from cursor type declaration then reference type is weak else Strong.
When does an application have a weak reference?
The application is said to have a strong reference to the object. A weak reference permits the garbage collector to collect the object while still allowing the application to access the object. A weak reference is valid only during the indeterminate amount of time until the object is collected when no strong references exist.
How to resolve a weak reference in C + +?
For a weak reference, call get_weak. C++/WinRT ensures that the resulting delegate holds a weak reference. At the last minute, and behind the scenes, the delegate attempts to resolve the weak reference to a strong one, and only calls the member function if it’s successful.
How to create a short or long weak reference?
You can create a short weak reference or a long weak reference: 1 Short The target of a short weak reference becomes null when the object is reclaimed by garbage collection. The weak… 2 Long A long weak reference is retained after the object’s Finalize method has been called. This allows the object to be… More