The theme of this ReactiveCocoa release is simplicity: getting rid of unused APIs and replacing complicated patterns with simpler ones where possible. Consequently, the changes are significant and far-reaching.
However, because migration is hard and time-consuming, 99% of RAC 2.x code will
continue to work under RAC 3.0 without any changes. You'll see deprecation
warnings by default, but even these can be temporarily disabled by defining
WE_PROMISE_TO_MIGRATE_TO_REACTIVECOCOA_3_0
before any framework headers are imported.
For a complete list of changes in ReactiveCocoa 3.0, see the milestone.
Because of its confusing API, RACCommand
hasn't been used much, despite the
value it offers in responding to UI events. The new RACAction
class, which
replaces
RACCommand
, attempts to provide the same value in a less confusing way.
Any signal generator can be directly converted into an
action via the -action
or -actionEnabledIf:
methods. Whenever the resulting
action is executed, a signal will be generated and subscribed to, triggering its
side effects. RACAction
will automatically ensure that only one subscription
is in effect at a time.
The class still provides most of the familiar RACCommand
conveniences, but
minimizes the use of signal blocks, signals of signals, and concurrent
behaviors, hopefully making it more approachable.
To update:
- Replace uses of
-[RACCommand initWithSignalBlock:]
that do not use the argument with a cold signal and-[RACSignal action]
. - Replace uses of
-[RACCommand initWithSignalBlock:]
that use the argument with+[RACDynamicSignalGenerator generatorWithBlock:]
and-[RACSignalGenerator action]
. - If you were instead using
-[RACCommand initWithEnabled:signalBlock:]
, use the-actionEnabledIf:
variant. - Replace uses of
RACCommand.executionSignals
that only care about values withRACAction.results
. - Replace uses of
RACCommand.executionSignals
that care about completion and error events withRACAction.executionSignals
. - Instead of setting
RACCommand.allowsConcurrentExecution
toYES
, use aRACSignalGenerator
for your behavior instead. - Replace
-[RACCommand execute:]
with-[RACAction signalWithValue:]
when you need the results of the execution. - Invoke
-[RACAction execute:]
from your UI when the caller does not care about the results. - Replace
rac_command
bindings withrac_action
.
For example, this command:
// View model
_logInCommand = [[RACCommand alloc] initWithEnabled:currentlyOnline signalBlock:^(id _) {
@strongify(self);
return [self logInWithUsername:self.username];
}];
// View controller
RAC(self.viewModel, username) = self.usernameField.rac_textSignal;
self.button.rac_command = self.viewModel.logInCommand;
Would look more like this, using RACAction
:
// View model
_logInAction = [[RACSignal
defer:^{
@strongify(self);
return [self logInWithUsername:self.username];
}]
actionEnabledIf:currentlyOnline];
// View controller
RAC(self.viewModel, username) = self.usernameField.rac_textSignal;
self.button.rac_action = self.viewModel.logInAction;
To accept input to the action, use a signal generator:
// View model
_logInAction = [[RACDynamicSignalGenerator
generatorWithBlock:^(NSString *username) {
@strongify(self);
return [RACSignal defer:^{
return [self logInWithUsername:username];
}];
}]
actionEnabledIf:currentlyOnline];
// View controller
self.button.rac_action = [[[self.usernameField.rac_textSignal
take:1]
postcompose:self.viewModel.logInAction]
actionEnabledIf:self.viewModel.logInAction.enabled];
+[RACSignal createSignal:]
has been
replaced with
a simpler +create:
method that no longer needs to return a disposable.
In conjunction with this new constructor, <RACSubscriber>
exposes
a disposable
property, to which any number of disposables can be added or
removed, and whose disposed
property can also be used as an early termination
flag. Both of these capabilities reduce the need for allocating additional
disposables.
Synchronous signals can also be terminated early now, because they don't have to
return a disposable before the subscriber can act. Instead, the subscriber's
disposable
can be disposed of at any time.
To update:
- Replace uses of
+createSignal:
with+create:
. - Instead of returning a disposable, attach it to the
disposable
of the<RACSubscriber>
, or figure out how to eliminate the disposable entirely. - The
-didSubscribeWithDisposable:
method of<RACSubscriber>
has been removed. If, for some reason, you were using it, refactor the call points to add to the subscriber'sdisposable
instead.
-throttle:valuesPassingTest:
and -flatten:
have been
replaced with the much
more general -flatten:withPolicy:
operator.
The plain -throttle:
operator has also been renamed to
-throttleDiscardingEarliest:
, alongside the new -throttleDiscardingLatest:
operator. These new names are intended to reduce confusion about what
"throttling" actually means in a given context.
To update:
- Replace uses of
-flatten:
with-flatten:withPolicy:
andRACSignalFlattenPolicyQueue
. - Replace uses of
-throttle:
with-throttleDiscardingEarliest:
. - Instead of using
-throttle:valuesPassingTest:
, create a signal of signals where some have delays, then use-flatten:withPolicy:
andRACSignalFlattenPolicyDisposeEarliest
.
For example, this partly-throttled signal:
// Throttles even numbers from the input signal. If an odd number arrives in the
// meantime, any even number that's queued will be discarded.
RACSignal *throttledEvens = [numbers
throttle:0.2 valuesPassingTest:^ BOOL (NSNumber *number) {
return number.integerValue % 2 == 0;
}];
Can be replaced with this signal of signals, and then flattened:
RACSignal *throttledEvens = [[numbers
map:^(NSNumber *number) {
if (number.integerValue % 2 == 0) {
// Delay even numbers.
return [[RACSignal return:number] delay:0.2];
} else {
// Forward odd numbers immediately.
return [RACSignal return:number];
}
}]
// When a new value arrives, discard any even number waiting to be sent.
// Limit the queue to 1 even number.
flatten:1 withPolicy:RACSignalFlattenPolicyDisposeEarliest];
Previously, RACObserve
had an implicit reference to self
, potentially
causing a retain
cycle when used
inside a block. This was used to ensure that the KVO observation always stopped
when self
deallocated, regardless of whether self
was the object being
observed.
The intention was to help with code like this:
// In a view or view controller:
[RACObserve(viewModel, text) subscribeNext:^(NSString *text) {
textField.text = text;
}];
Where the viewModel
could deallocate much later than self
—or possibly
never—causing the subscription to live much longer than one might expect.
However, it was determined that real code doesn't benefit from this behavior
often enough to justify the subtle memory management issues, so RACObserve
no
longer captures
self
unless it's the actual target of observation.
To update:
- When observing
self
, no changes are necessary. - When observing other objects, use features like
RAC()
orrac_liftSelector:
to ensure that the observations still have a finite lifetime.
For example, the above code could be modified in one of the following ways:
// Automatically stops observing when `self.textField` deallocates.
RAC(self.textField, text) = [RACObserve(viewModel, text) map:^(NSString *text) {
return text ?: @"";
}];
// Automatically stops observing when `self.textField` deallocates.
[self.textField rac_liftSelector:@selector(setText:) withSignals:RACObserve(viewModel, text), nil];
RACSequence
was created a while ago to provide a pull-driven alternative to
the push-driven signals that RAC is built around. However, it's difficult to
convert between the two, and it leads to a lot of confusion around operator
types, and the purpose of the RACStream
superclass.
Since most consumers end up using signals far more than sequences, and it's
simpler to only offer one, RACSequence
has been
deprecated, and all
stream operators now appear directly on RACSignal
for clarity.
Instead of the rac_sequence
methods that appeared on NSArray
,
NSDictionary
, NSSet
, etc., there's now a rac_signal
method. When lazy
evaluation is actually algorithmically important, a third-party library (like
RXCollections) can be used instead.
To update:
- Replace uses of
RACStream
andRACSequence
withRACSignal
. - Replace uses of
rac_sequence
extension methods withrac_signal
methods.
Although RACMulticastConnection
solves an important problem (sharing side
effects between multiple subscribers), it obfuscates what's really happening and
frequently confuses newcomers, so it has been
deprecated in favor of
using subjects directly.
To update:
- Replace
-publish
and-multicast:
with-subscribe:
plus aRACSubject
. - Ensure that subscription occurs in the same place that the underlying signal was being connected to.
RACReplaySubject
has been used mostly for memoization: doing
something once, then saving the results. However, this has made it something of
an odd duck next to RACSignal
and RACSubject
.
Where RACSignal
usually represents a "cold" signal (one that performs its side
effects once for each subscription), and RACSubject
represents a "hot" signal
(one that doesn't perform any side effects upon subscription),
RACReplaySubject
has occupied a weird "lukewarm" middle ground.
Additionally, replayed signals don't support certain kinds of manipulation, like
-retry:
, -repeat
, -subscribeOn:
, etc. Such operators will have—at best—
surprising behavior, since they don't actually allow the underlying subscription
to be controlled.
For these reasons, RACReplaySubject
and its corresponding signal operators
have been deprecated.
(Note that the replacement offered in that pull request, RACPromise
, was later
removed as well.)
To update:
- Replace
RACReplaySubject
,-replay
,-replayLazily
, and-replayLast
with cold signals or plainRACSubject
if possible. - Replace
+startEagerlyWithScheduler:block:
and+startLazilyWithScheduler:block:
with+create:
plus-subscribeOn:
.
By far, the easiest solution is to adopt cold signals everywhere, and limit the number of subscriptions to signals that have side effects.
For example, given this replaying signal:
RACSignal *lazyFetch = [[[self
fetchUser]
flattenMap:^(User *user) {
return [self saveUser:user];
}]
replayLazily];
Removing the -replayLazily
doesn't alter the behavior for one subscription.
If multiple subscribers are interested in the results, connect them to a subject,
and then forward the signal to that subject:
RACSubject *lazyFetchSubject = [RACSubject subject];
[lazyFetchSubject subscribeCompleted:^{
NSLog(@"First subscriber completed");
}];
[lazyFetchSubject subscribeCompleted:^{
NSLog(@"Second subscriber completed");
}];
[lazyFetch subscribe:lazyFetchSubject];
RACBehaviorSubject
has never gotten much attention, in implementation or
usage, so it has been
deprecated. Most of
its semantics can be implemented with other classes or operators.
To update:
Replace uses of RACBehaviorSubject
with a property or a plain RACSubject
.
The new
RACSignalGenerator
class encapsulates the logic for creating a signal from
some input value.
Although similar in principle, a signal generator boasts a couple major
advantages over a plain block of type RACSignal * (^)(id input)
:
- Operators can be added to
RACSignalGenerator
. This can be used for greater composability, like the built-in-postcompose:
method that chains two generators together. - A signal generator's algorithm can reference itself using
-[RACDynamicSignalGenerator initWithReflexiveBlock:]
, which is extremely useful for creating signals of indefinite length, and much less error-prone than a recursive block.
See RACSignal+Operations.m for examples of operators that use generators internally.
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.
- Simplified and safer KVO
- Safer commands with less state
- Fallback nil value for RAC macro
- Explicit schedulers for time-based operators
- More powerful selector signals
- Simpler two-way bindings
- Better bindings for AppKit
- More obvious sequencing operator
- Renamed signal binding method
- Consistent selector lifting
- Renamed scheduled signal constructors
- Notification immediately before object deallocation
- Extensible queue-based schedulers
- GCD time values replaced with NSDate
- Windows and numbered buffers removed
- NSTask extension removed
- RACSubscriber class now private
- Commands for UIButton
- Signal for UIActionSheet button clicks
- Better documentation for asynchronous backtraces
- Fixed libextobjc duplicated symbols
- Bindings for UIKit classes
- Signal subscription side effects
- Test scheduler
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)
withRACObserve(self, key)
. - Replace uses of
RACAble(self.key)
with[RACObserve(self, key) skip:1]
(if skipping the starting value is necessary).
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 thesignalBlock
passed to the initializer. - Instead of subscribing to the result of
-addSignalBlock:
, subscribe toexecutionSignals
or the result of-execute:
instead. - Replace uses of
RACAbleWithStart(command, executing)
withcommand.executing
. - Replace uses of
RACAbleWithStart(command, canExecute)
withcommand.enabled
. - Remove uses of
deliverOn:RACScheduler.mainThreadScheduler
onRACCommand
properties, as they are now unnecessary.
The RAC
macro now always
requires two or three
arguments:
- The object to bind to.
- The key path to set when new values are sent.
- (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)
withRAC(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)
-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.
-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, thesuper
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 aRACSubject
instead.
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 aRACChannel
. Replace N-way property subjects (where N is greater than 2) with multipleRACChannel
s. - Instead of creating a
RACObservablePropertySubject
, create aRACKVOChannel
or use theRACChannelTo
macro. - Replace uses of
RACBinding
withRACChannelTerminal
. - Replace uses of
RACBind(self.objectProperty)
withRACChannelTo(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];
-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:@{ NSContinuouslyUpdatesValueBindingOption: @YES }
for-rac_bind:toObject:withKeyPath:
@{ NSContinuouslyUpdatesValueBindingOption: @YES, NSNullPlaceholderBindingOption: nilValue }
for-rac_bind:toObject:withKeyPath:nilValue:
@{ NSContinuouslyUpdatesValueBindingOption: @YES, NSValueTransformerBindingOption: valueTransformer }
for-rac_bind:toObject:withKeyPath:transform:
@{ NSContinuouslyUpdatesValueBindingOption: @YES, NSValueTransformerBindingOption: NSNegateBooleanTransformerName }
for-rac_bind:toObject:withNegatedKeyPath:
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:
.
-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]
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:
.
+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.
-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
withrac_willDeallocSignal
. - Replace uses of
-rac_addDeallocDisposable:
by invoking-addDisposable:
on the object'srac_deallocDisposable
instead.
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:]
.
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
.
-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:
- Refactor uses of
-windowWithStart:close:
with different patterns. - Replace uses of
-buffer:
with take, collect, and repeat.
NSTask+RACSupport
has been
removed, because it
was buggy and unsupported.
To update:
Use a vanilla NSTask
, and send events onto RACSubject
s instead.
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
.
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.
UIActionSheet
now has a rac_buttonClickedSignal
property, which will
fire whenever one of the sheet's buttons is clicked.
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.
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.
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.
RACSignal
now has the
-initially:
operator, which executes a given block each time the signal is subscribed to.
This is symmetric to -finally:
.
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.