Explanation of a line of Objective C code [closed] - ios

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for (ItemEntity *itemEntity in changedItemEntities) {
[[NetworkWrapper sharedInstance] uploadItemEntity:itemEntity userId:[itemEntity.userId unsignedIntegerValue] title:itemEntity.title completion:^(BOOL success, NSUInteger photoId, NSUInteger timeStamp) {
if (success) {
itemEntity.itemId = [NSNumber numberWithUnsignedInteger:photoId];
itemEntity.isUploaded = YES;
[self.context processPendingChanges];
NSError *error;
[self.context save:&error];
}
}];
}
What do these lines of code do in simple programming terms?

Answer 1

One of Objective-C's strengths is its verbose syntax, making the code very readable.
for (ItemEntity *itemEntity in changedItemEntities) {
This will perform the operation in braces ({}) for each ItemEntity object in changedItemEntities. Inside the braces, each object can be referred to as itemEntity.
[NetworkWrapper sharedInstance]
This gets a reference to the shared instance of a class called NetworkWrapper
uploadItemEntity:itemEntity userId:[itemEntity.userId unsignedIntegerValue] title:itemEntity.title completion:
This tells the shared instance to upload each entity, with a user ID and title derived from the entity object itself. There is a completion block, which is run once the operation is done, and looks like this:
^(BOOL success, NSUInteger photoId, NSUInteger timeStamp) {
if (success) {
itemEntity.itemId = [NSNumber numberWithUnsignedInteger:photoId];
itemEntity.isUploaded = YES;
[self.context processPendingChanges];
NSError *error;
[self.context save:&error];
}
This will run for each completed upload. That code will have a success flag (a boolean value), a photo ID (an integer) and a timestamp (also an integer). In your example the values are used to update the itemEntity object and then the context lines cause the Core Data store of the app to save its data to disk.
So basically you've got a bunch of things, you're performing an upload operation for each one, and when each upload is done, you're running another block of code.

Answer 2

It iterates through the collection named changedItemEntities, perhaps an NSArray—we can't know for sure as you don't show the definition, and for each ItemEntity in that collection, it sends the uploadItemEntity:userId:title:completion: selector to the NetworkWrapper singleton. The singleton is accessed via [NetworkWrapper sharedInstance], which is the standard Objective-C singleton pattern Apple uses. It will return the same pointer each time, so it could be moved out of the loop and stored in a local. The completion is a block (a lambda function) to be executed when the upload completes, presumably. Presumably the singleton passes the result of the upload operation—a boolean indicating success or failure, the photoId the server generated, and a timestamp, perhaps of the upload operation. That block would then do something with this information. In this case it seems to update the entity and commit some changes back via CoreData stuff.
You probably want to step through this code to understand it better. Set a break point on the first line and use the Step Over / Step Into buttons in Xcode to trace through it.
If you have specific questions, you should ask new specific questions.