Core Data and Magical Record saving

Question

This is somewhat of a basic question, but need some clarification.

I have this piece of code.

   //line of code #1

[localContext MR_saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) {

   //line of code #2

}];

Is the line of code #2 the completion block? Should I make my changes to an entity prior to the save as line of code #1 shows?

Thanks

Answer 1

Anything with the form of ^(…) { … } or ^{ … } is a block. In essence, a block is portable a chunk of code which is not directly executed. A block can be saved to a variable then execute at a later point in time.

typedef void (^my_block_t)();
my_block_t myBlock = ^{
    NSLog(@"I'm in a block");
};

Here's a block which prints a log statement. The block is saved to the variable myBlock. Note: at this point in time, NSLog does not print out anything.

At some point in time later, myBlock can be execute.

myBlock();

At this point in the code, the block is run and NSLog prints out it's statement.

If your example, the execution of line of code #2 is delayed until after the save has completed.

Logically, it works the same as:

Step 1) execute line of code #1
Step 2) execute save
Step 3) execute line of code #2

Because things in line of code #2 happen after the save has completed, then any changes to the model would not be saved at that point.