You want to understand the difference between accessing variables in Objective-C methods and accessing those variables in block objects.
Here is a brief summary of what you must know about variables in block objects:
Local variables in block objects work exactly the same as in Objective-C methods.
For inline block objects, local variables constitute not only variables defined within the block, but also the variables that have been defined in the method that implements that block object. (Examples will come shortly.)
You cannot refer to
self in independent block objects implemented in an Objective-C class. If you need to
self, you must pass that
object to the block object as a parameter. We will see an example
of this soon.
You can refer to
an inline block object only if
self is present in the lexical scope
inside which the block object is created.
For inline block objects, local variables that are defined inside the block object’s implementation can be read from and written to. In other words, the block object has read-write access to variables defined inside the block object’s body.
For inline block objects, variables local to the Objective-C
method that implements that block can only be read from, not
written to. There is an exception, though: a block object can
write to such variables if they are defined with the
__block storage type. We will see an
example of this as well.
Suppose you have an object of type