Eliasz Sawicki

Eliasz Sawicki

iOS developer from Gdansk

ReactiveCocoa 4 - MutableProperty

- 1 min

MutableProperty which comes with ReactiveCocoa allows us to track variable’s changes. Let’s take a quick look on how it actually works.

Let’s assume, that we want to create a bank account balance variable, that we will be tracking later on.

MutableProperty has three fields that we are especially interested in.


First one is value, which grants us access to a current value of our property. Everytime we change a this value, all observers of signals created by a producer get notified about it.


Second field is producer, which is a factory for started signals which we use in order to track our property. Lets use our factory to create a signal out of our MutableProperty. Everytime our property changes, it will be printed. If property is deinitialized, signals created by producer are completed.


Our observer is initialized as a buffer with a capacity of 1. What does it mean? When we set our value, we also push it to an observer. Our observer has an internal buffer, which in this case remembers last pushed value. This value will be passed to observer every time producer starts a new signal.

Passing values to our buffered observer is handled internally and happens everytime a setter for a value is called. So in fact mostly we will be having fun with value and producer fields.

This article is cross-posted with my my company blog

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