GRKArrayDiff

Given two NSArrays, a previous and a current, GRKArrayDiff will report all deletions, insertions, moves, and modifications. This is specifically targeted for array backed data models which are used to support Table Views and Collection Views, but is generally applicable as well.

Installing

If you're using CocoPods it's as simple as adding this to your Podfile:

pod 'GRKArrayDiff'

otherwise, simply add the contents of the GRKArrayDiff subdirectory to your project.

Documentation

To use, simply import GRKArrayDiff.h:

#import "GRKArrayDiff.h"

Then alloc and init a new instance, passing in the previous array, the new array, and two blocks. The identityBlock is responsible for uniquely identifying the given object while the modifiedBlock is responsible for reporting if the given currentObj object is to be considered as modified.

GRKArrayDiff *diff = [[GRKArrayDiff alloc] initWithPreviousArray:previousArray currentArray:currentArray identityBlock:^NSString *(id obj) {
	return [obj identifier];
} modifiedBlock:^BOOL(id  _Nonnull previousObj, id  _Nonnull currentObj) {
	return [[currentObj identifier] isEqualToString:@"five"] ||
	[[currentObj identifier] isEqualToString:@"three"] ||
	[[currentObj identifier] isEqualToString:@"zero"] ||
	[[currentObj identifier] isEqualToString:@"one"];
}];

Once created, the instance's four properties (deletions, insertions, moves, and modifications) will be populated with NSSets of GRKArrayDiffInfo objects which describe the changes to the elements between the previous and current arrays.

Typical iOS table view update usage would look something like this:

//Save the current data model for comparison
NSArray *oldDataModel = self.dataModel;

//Update our data model with the latest
self.dataModel = [self updateDataModel];

//Get differences in data model
GRKArrayDiff *diff = [[GRKArrayDiff alloc] initWithPreviousArray:oldDataModel currentArray:self.dataModel identityBlock:^NSString *(id obj) {
    NSString *identifier = nil;
    if ([obj conformsToProtocol:@protocol(MyType)])
    {
        id <MyType> myObj = (id <MyType>)obj;
        identifier = [myObj uuid];
    }
    return identifier;
} modifiedBlock:^BOOL(id  _Nonnull previousObj, id  _Nonnull currentObj) {
    BOOL modified = currentObj != nil && [modificationSet containsObject:currentObj];
    return modified;
}];

//Update the UI with the changes
[diff updateTableView:self.tableView section:0 animation:animated ? UITableViewRowAnimationAutomatic : UITableViewRowAnimationNone completion:nil];

Additional documentation is available in GRKArrayDiff.h and example usage can be found in the GRKArrayDiffTest.m.

Disclaimer and Licence

• I have made use of hashing code from https://github.com/levigroker/HashBuilder
• Inspiration for table view updates taken from TLIndexPathTools
• This work is licensed under the Creative Commons Attribution 3.0 Unported License. Please see the included LICENSE.txt for complete details.

About

A professional iOS engineer by day, my name is Levi Brown. Authoring a blog grokin.gs, I am reachable via:

Twitter @levigroker
Email [email protected]

Your constructive comments and feedback are always welcome.