How to use MutableLiveData and LiveData in Android?

Question

I have used MutableLiveData and LiveData in the 3 ways below and see no difference.

    // 1
    private val _way1 = MutableLiveData<Boolean>()
    val way1 get() = _way1

    // 2
    private val _way2 = MutableLiveData<Boolean>()
    val way2: LiveData<Boolean> = _way2

    // 3
    var way3 = MutableLiveData<Boolean>()
        private set

Can you explain it to me?

Answer 1

1/

• _way1 is private and its value can be changed
• way1 is just a public version of _way1, everything is the same. This class and other classes can access and change its value whatever they want.

This usage is meaningless in practice.

2/

• _way2 is private and its value can be changed
• way2 is public, and it's just a LiveData so it doesn't have setValue and postValue methods so its value cannot be changed. (LiveData is the parent class of MutableLiveData).

This is a recommended way, it lets other classes observe this live data by accessing way2 but cannot change it, only the current class can change the value by modifying _way2, protecting it from being changed outside of your scope.

Read more about object encapsulation in OOP

3/

• way3 is public and its value can be changed
• Using var here because the developer wants to recreate it. Although you protect the variable by adding private set, other classes can still change the value by accessing the variable and calling setValue or postValue because it's still a Mutable one.

So this usage is still dangerous and to my point, unnecessary to use var for a LiveData object.

Answer 2

There are fundamental differences between MutableLiveData and LiveData that lie in their mutability and usage scenarios:

1. Mutability:

• MutableLiveData: As the name suggests, it's a mutable live data holder. You can modify its value using methods like setValue and postValue. This makes it ideal for scenarios where the data needs to be updated dynamically, like a counter or a user's current location.
• LiveData: It's an immutable live data holder. Its value cannot be directly changed after it's set. This makes it ideal for situations where data consistency and unidirectional flow are crucial, like observing changes in a database or network response.

2. Usage Scenarios:

• MutableLiveData: Used in situations where data needs to be updated and observed by multiple components. Typically used in ViewModels to expose data to the UI and handle updates.
• LiveData: Used for observing data changes without modifying it. Ideal for situations where data is retrieved from a single source of truth, like a repository and different components need to react to its changes.

3. Exposed API:

• MutableLiveData: Exposes methods like setValue, postValue, and getValue to modify the value. This can lead to potential data inconsistencies if not used carefully.
• LiveData: Offers only observation methods like observeForever and observe to listen to changes without modifying the data directly. This promotes safer data handling and unidirectional data flow.

In summary:

• Use MutableLiveData when data needs to be updated dynamically and multiple components need to observe it.
• Use LiveData when data is retrieved from a single source of truth and components need to react to its changes without modifying it directly.

Both approaches provide a way to access the data, but they differ in their mutability and intended use cases. Choose the one that best suits your specific data management needs and ensures data consistency and unidirectional flow.

I hope this clarifies the difference between MutableLiveData and LiveData!