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2.0

This release of ReactiveCocoa contains major breaking changes that we were unable to make after freezing the 1.0 API. All changes are focused on eliminating bad code and bad usage patterns, reducing confusion, and increasing flexibility in the framework.

For a complete list of changes in ReactiveCocoa 2.0, see the milestone.

Breaking changes

  1. Simplified and safer KVO
  2. Safer commands with less state
  3. Fallback nil value for RAC macro
  4. Explicit schedulers for time-based operators
  5. More powerful selector signals
  6. Simpler two-way bindings
  7. Better bindings for AppKit
  8. More obvious sequencing operator
  9. Renamed signal binding method
  10. Consistent selector lifting
  11. Renamed scheduled signal constructors
  12. Notification immediately before object deallocation
  13. Extensible queue-based schedulers
  14. GCD time values replaced with NSDate
  15. Windows and numbered buffers removed
  16. NSTask extension removed
  17. RACSubscriber class now private

Additions and improvements

  1. Commands for UIButton
  2. Signal for UIActionSheet button clicks
  3. Better documentation for asynchronous backtraces
  4. Fixed libextobjc duplicated symbols
  5. Bindings for UIKit classes
  6. Signal subscription side effects
  7. Test scheduler

Breaking changes

Simplified and safer KVO

RACAble and RACAbleWithStart have been replaced with a single RACObserve macro. RACObserve always starts with the current value of the property, and will notice the deallocation of weak properties (unlike vanilla KVO).

Unlike the previous macros, which only required one argument for key paths on self, RACObserve always requires two arguments.

To update:

  • Replace uses of RACAbleWithStart(self.key) with RACObserve(self, key).
  • Replace uses of RACAble(self.key) with [RACObserve(self, key) skip:1] (if skipping the starting value is necessary).

Safer commands with less state

RACCommand has been completely refactored. It is no longer a RACSignal, and the behavior of -addSignalBlock: has been moved to the initializer, making the class almost entirely immutable.

Reflecting the most common use case, KVO-notifying properties have been changed into signals instead. During the change, canExecute was also renamed to enabled, which should make its purpose more obvious for binding to the UI.

In addition, changes to executing, errors, and enabled are now guaranteed to fire on the main thread, so UI observers no longer run in the background unexpectedly.

All together, these improvements should make RACCommand more composable and less imperative, so it fits into the framework better.

To update:

  • Move execution logic from -addSignalBlock: or -subscribeNext: into the signalBlock passed to the initializer.
  • Instead of subscribing to the result of -addSignalBlock:, subscribe to executionSignals or the result of -execute: instead.
  • Replace uses of RACAbleWithStart(command, executing) with command.executing.
  • Replace uses of RACAbleWithStart(command, canExecute) with command.enabled.
  • Remove uses of deliverOn:RACScheduler.mainThreadScheduler on RACCommand properties, as they are now unnecessary.

Fallback nil values for RAC macro

The RAC macro now always requires two or three arguments:

  1. The object to bind to.
  2. The key path to set when new values are sent.
  3. (Optional) A value to set when nil is sent on the signal.

This is necessary to avoid a -setNilValueForKey: exception when observing a primitive property through an intermediate object which gets set to nil.

This is not actually a change in key-value observing behavior — it's a caveat with KVO regardless — but RACObserve makes it more prominent, because the deallocation of weak properties will be considered a change to nil.

To update:

  • Replace uses of RAC(self.objectProperty) with RAC(self, objectProperty).
  • When binding a signal that might send nil (like a key path observation) to a primitive property, provide a default value: RAC(self, integerProperty, @5)

Explicit schedulers for time-based operators

-bufferWithTime:, +interval:, and -timeout: have been unintuitive and error-prone because of their implicit use of a background scheduler.

All of the aforementioned methods now require a scheduler argument, so that it's clear how events should be delivered.

To update:

  • To match the previous behavior exactly, pass in [RACScheduler scheduler]. Note that this creates a new background scheduler for events to arrive upon.
  • If you were already using -deliverOn: to force one of the above operators to deliver onto a specific scheduler, you can eliminate that hop and pass the scheduler into the operator directly.

More powerful selector signals

-rac_signalForSelector: has been completely refactored to support listening for invocations of existing methods, new and existing methods with multiple arguments, and existing methods with return values.

+rac_signalForSelector: (the class method variant) was removed, because swizzling class methods is dangerous and difficult to do correctly.

To update:

  • Most existing uses of -rac_signalForSelector: shouldn't require any changes. However, the super implementation (if available) of any targeted selector will now be invoked, where it wasn't previously. Verify that existing uses can handle this case.
  • Replace uses of +rac_signalForSelector: by implementing the class method and sending arguments onto a RACSubject instead.

Simpler two-way bindings

RACPropertySubject and RACBinding have been replaced with RACChannel and RACChannelTerminal. Similarly, RACObservablePropertySubject has been replaced with RACKVOChannel.

In addition to slightly better terminology and more obvious usage, channels only offer two-way bindings by default, which is a simplification over the previous N-way binding interface.

Because of the sweeping conceptual changes, the old APIs have been completely removed without deprecation.

To update:

  • Instead of creating a RACPropertySubject, create a RACChannel. Replace N-way property subjects (where N is greater than 2) with multiple RACChannels.
  • Instead of creating a RACObservablePropertySubject, create a RACKVOChannel or use the RACChannelTo macro.
  • Replace uses of RACBinding with RACChannelTerminal.
  • Replace uses of RACBind(self.objectProperty) with RACChannelTo(self, objectProperty). Add a default value for primitive properties: RACChannelTo(self, integerProperty, @5)
  • Replace uses of -bindTo: with the explicit subscription of two endpoints:
[binding1.followingEndpoint subscribe:binding2.leadingEndpoint];
[[binding2.leadingEndpoint skip:1] subscribe:binding1.followingEndpoint];

Better bindings for AppKit

-rac_bind:toObject:withKeyPath: and related methods have been replaced with -rac_channelToBinding:options:, which returns a RACChannelTerminal that can be used as a two-way binding or a one-way signal.

To update:

  • If possible, refactor code to use the new RACChannel interface. This bridges Cocoa Bindings with the full power of ReactiveCocoa.
  • For a direct conversion, use -bind:toObject:withKeyPath:options: with the following options:
    1. @{ NSContinuouslyUpdatesValueBindingOption: @YES } for -rac_bind:toObject:withKeyPath:
    2. @{ NSContinuouslyUpdatesValueBindingOption: @YES, NSNullPlaceholderBindingOption: nilValue } for -rac_bind:toObject:withKeyPath:nilValue:
    3. @{ NSContinuouslyUpdatesValueBindingOption: @YES, NSValueTransformerBindingOption: valueTransformer } for -rac_bind:toObject:withKeyPath:transform:
    4. @{ NSContinuouslyUpdatesValueBindingOption: @YES, NSValueTransformerBindingOption: NSNegateBooleanTransformerName } for -rac_bind:toObject:withNegatedKeyPath:

More obvious sequencing operator

To make the sequencing and transformation operators less confusing, -sequenceMany: has been removed, and -sequenceNext: has been renamed to -then:.

To update:

  • Replace uses of -sequenceMany: with -flattenMap: and a block that doesn't use its argument.
  • Replace uses of -sequenceNext: with -then:.

Renamed signal binding method

-toProperty:onObject: and -[NSObject rac_deriveProperty:from:] have been combined into a new -[RACSignal setKeyPath:onObject:nilValue:] method.

The nilValue parameter was added in parallel with the RAC macro, but the semantics are otherwise identical.

To update:

  • Replace -toProperty:onObject: and -rac_deriveProperty:from: with -setKeyPath:onObject:.
  • When binding a signal that might send nil (like a key path observation) to a primitive property, provide a default value: [signal setKeyPath:@"integerProperty" onObject:self nilValue:@5]

Consistent selector lifting

In the interests of parametricity, -rac_liftSelector:withObjects: has been replaced with -rac_liftSelector:withSignals:, which requires all arguments to be signals. This makes usage more consistent.

-rac_liftBlock:withArguments: has been removed, because it's redundant with RACSignal operators.

The -rac_lift proxy has also been removed, because there's no way to make it consistent in the same way.

To update:

  • Wrap non-signal arguments with +[RACSignal return:] and add a nil terminator.
  • Replace block lifting with +combineLatest:reduce:.
  • Replace uses of -rac_lift with -rac_liftSelector:withSignals:.

Renamed scheduled signal constructors

+start:, +startWithScheduler:block, and +startWithScheduler:subjectBlock: have been combined into a single +startEagerlyWithScheduler:block: constructor.

The key improvements here are a more intuitive name, a required RACScheduler to make it clear where the block is executed, and use of <RACSubscriber> instead of RACSubject to make it more obvious how to use the block argument.

To update:

  • Use [RACScheduler scheduler] to match the previous implicit scheduling behavior of +start:.
  • Refactor blocks that return values and set success/error, to send events to the given <RACSubscriber> instead.

Notification immediately before object deallocation

-rac_didDeallocSignal has been removed in favor of -rac_willDeallocSignal, because most teardown should happen before the object becomes invalid.

-rac_addDeallocDisposable: has also been removed in favor of using the object's rac_deallocDisposable directly.

To update:

  • Replace uses of -rac_didDeallocSignal with rac_willDeallocSignal.
  • Replace uses of -rac_addDeallocDisposable: by invoking -addDisposable: on the object's rac_deallocDisposable instead.

Extensible queue-based schedulers

RACQueueScheduler has been exposed as a public class, so consumers can create their own scheduler implementations using GCD queues.

The RACTargetQueueScheduler subclass replaces the +schedulerWithQueue:name: method.

To update:

Replace uses of +schedulerWithQueue:name: with -[RACTargetQueueScheduler initWithName:targetQueue:].

GCD time values replaced with NSDate

NSDate now replaces dispatch_time_t values in RACScheduler, because dates are easier to use, more convertible to other formats, and can be used to implement a virtualized time scheduler.

To update:

Replace dispatch_time_t calculations with NSDate.

Windows and numbered buffers removed

-windowWithStart:close: and -buffer: have been removed because they're not well-tested, and their functionality can be achieved with other operators.

-bufferWithTime: is still supported.

To update:

NSTask extension removed

NSTask+RACSupport has been removed, because it was buggy and unsupported.

To update:

Use a vanilla NSTask, and send events onto RACSubjects instead.

RACSubscriber class now private

The RACSubscriber class (not to be confused with the protocol) should never be used directly, so it has been hidden.

To update:

Replace uses of RACSubscriber with id<RACSubscriber> or RACSubject.

Additions and improvements

Commands for UIButton

UIButton now has a rac_command property.

Any command set will be executed when the button is tapped, and the button will be disabled whenever the command is unable to execute.

Signal for UIActionSheet button clicks

UIActionSheet now has a rac_buttonClickedSignal property, which will fire whenever one of the sheet's buttons is clicked.

Better documentation for asynchronous backtraces

Documentation has been added to RACBacktrace explaining how to start collecting backtraces and print them out in the debugger.

The +captureBacktrace… methods have been renamed to +backtrace…, and +printBacktrace has been removed in favor of using po [RACBacktrace backtrace] from the debugger.

The rac_ GCD functions which collect backtraces have also been exposed, primarily for use on iOS.

Fixed libextobjc duplicated symbols

If libextobjc was used in a project that statically linked ReactiveCocoa, duplicate symbol errors could result.

To avoid this issue, RAC now renames the libextobjc symbols that it uses.

Bindings for UIKit classes

RACChannel interfaces have been added to many UIKit classes, greatly simplifying glue code between your models and views.

For example, assuming you want to bind a person model's name property:

UITextField *nameField = ...;
RACChannelTerminal *nameTerminal = RACChannelTo(model, name);
RACChannelTerminal *nameFieldTerminal = [nameField rac_newTextChannel];
[nameTerminal subscribe:nameFieldTerminal];
[nameFieldTerminal subscribe:nameTerminal];

You may also bind multiple controls to the same property, for example a UISlider for coarse editing and a UIStepper for fine-grained editing.

Signal subscription side effects

RACSignal now has the -initially: operator, which executes a given block each time the signal is subscribed to. This is symmetric to -finally:.

Test scheduler

RACTestScheduler is a new kind of scheduler that virtualizes time. Enqueued blocks can be stepped through at any pace, no matter how far in the future they're scheduled for, making it easy to test time-based behavior without actually waiting in unit tests.