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androidkotlinandroid-jetpack-composeandroid-viewmodelmutablestateflow

What is better to update a view model's MutableStateFlow, _uiState.update{} or _uiState.value = _uiState.value.copy()?

I am confused what to use, whether to use update or copy for changing/updating the state of UI in Jetpack Compose.

Some say to use

_uiState.update {
    it.copy()
}

Some say to use

_uiState.value = _uiState.value.copy()

Which one would be better to use and why?

I have used copy() a lot of times but still I am not sure if I am updating the uiState efficiently or properly.

Solution

  • Actually both _uiState.update { } and _uiState.value.copy() are valid for updating state, but they are slightly different in terms of best practices and thread safety.

    Using _uiState.update { }

    Thread-safety: It prevents issues where multiple threads could attempt to update the state simultaneously, leading to inconsistent states.

    Atomicity: It reads the current state and applies modifications in one operation.

    Using _uiState.value.copy()

    it is not inherently thread-safe. If multiple threads try to update _uiState at the same time, there could be inconsistencies.

    This approach is simpler in single-threaded scenarios, it’s generally less safe in multi-threaded environments, which can be easily occur in background threads, coroutines

    So, which one you should use and when



    Prefer _uiState.update { }: In most cases, it's better to use update { } when dealing with MutableStateFlow because it is thread-safety and atomic. It will protect UI state from race conditions and also ensure consistent updates even in a multi-threaded environment.

    Use _uiState.value.copy() -> Very Carefully : This can be fine if you're sure that no other threads will be modifying the state concurrently, single Thread environment.