strong and weak in iOS

strong and weak.

• this is a two memory management attributes for properties introduced by in ARC.
• weak
• Weak reference are not support in OSX v.10.6 and iOS4>Weak reference does not extend the lifetime of object it points to, and automatically becomes nil when there are no strong reference to the object.
• Weak reference most commonly used in the connection with thing such as a notification.you will keep weak reference to an object and keep it sending it messages as long as it is referenced elsewhere,then you can have cleaned up automatically later.
• It says to the compiler keep this member as long as possible.
• On weak members we can’t call retain or release methods
• When the weak member is de-allocated then automatically pointer will set to nil.
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