CODEWITHSUNDEEP
androidkotlin-coroutines
Max Turchin
Max Turchin

Reputation: 61

If statement in viewModelScope

Why function return always false? And how to fix this?

fun testFun(id: Int): Boolean {
    var isExists = false
    viewModelScope.launch {
        val itemFromDb = database.getDetails(id)
        if (itemFromDb != null) // never executing
            isExists = true
    }
    return isExists // always return false
}

Upvotes: 2

Views: 301

Answers (3)

Max Turchin
Max Turchin

Reputation: 61

This solution suits me.

suspend fun testFun(id: Int): Boolean {
    var isExists = false
    val result = viewModelScope.await {
        val itemFromDb = database.getDetails(id)
        if (itemFromDb != null)
            isExists = true
        return@async isExists
    }
    result.await()
    return isExists
}

Upvotes: 0

Abdul
Abdul

Reputation: 887

So this is also a possible solution. I have tried it here and working fine

 fun something(): Boolean = runBlocking (Dispatchers.IO){
        return@runBlocking database.getDetails(id)!=null
    }

Upvotes: 1

CoolMind
CoolMind

Reputation: 28875

As @Abdul said, your coroutine switches to another thread and continues there. But a testFun method doesn't stop working and finishes before the coroutine finish.

You can rewrite your code. For instance, make testFun a suspended function and write everything inside in one block. Or synchronize the method and the coroutine. I usually do this with withContext(Dispatchers.IO), didn't work with viewModelScope.launch either.

Maybe wrong solutions:

fun suspend something(): Boolean {
    var result = false

    result = withContext(Dispatchers.IO) {
        ...
        true
    }
    ... // Other code in the main thread.

    return result
}

fun something(): Boolean {
    var result = false
    val job = launch() {
        result = withContext(Dispatchers.IO) {
            ...
            true
        }
        ... // Other code in the main thread.
    }
    return result
}

Upvotes: 2

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