Kotlin how to try/catch a cast

Question

I am storing shared preferences value as a HashSet and when retrieving I see the warning about unchecked casting. What is the most simple and what is the safest solution to ensure bug free implementation here?

class TaskListDataManager(private val context: Context) {
    fun saveList(taskList: TaskList) {
        val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context).edit()

        sharedPreferences.putStringSet(taskList.name, taskList.taskList.toHashSet())

        sharedPreferences.apply()
    }

    fun readList(): ArrayList<TaskList> {
        val sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context)
        val taskLists = sharedPreferences.all.map {
            TaskList(it.key, ArrayList(it.value as HashSet<String>))
        }

        return ArrayList<TaskList>(taskLists)
    }
}

https://stackoverflow.com/questions/36569421/kotlin-how-to-work-with-list-casts-unchecked-cast-kotlin-collections-listkot — ADM, Jan 27 '21 at 04:49

score 3 · Answer 1 · answered Jan 27 '21 at 05:40

3

Apart from the try/catch block, you can also safely unwrap it while putting in the model.

(a.value as? HashSet<String>)?.let {
   TaskList(a.key, ArrayList(it))
}

answered Jan 27 '21 at 05:40

Himanshu Choudhary

360
1
8

Thx @Himanshu. This is an elegant solution. – Cory Robinson Jan 27 '21 at 14:31

score 1 · Accepted Answer · answered Jan 27 '21 at 04:38

1

You can try this

try{    
   //code that may throw exception    
}catch(e: SomeException){  
   //code that handles exception  
}finally {  
   // optional finally block  
}

answered Jan 27 '21 at 04:38

How do you know the exception type that a bad cast will throw? – Cory Robinson Jan 27 '21 at 04:41
1

@CoryRobinson `e: Exception`. It will cast any type of `exception`. – Jan 27 '21 at 04:43

score 0 · Answer 3 · answered Jan 27 '21 at 08:58

0

You can try

kotlin.runCatching { }.onFailure {  }

answered Jan 27 '21 at 08:58

tadev

204
1
5

7

While this code may provide a solution to the question, it's better to add context as to why/how it works. This can help future users learn, and apply that knowledge to their own code. You are also likely to have positive feedback from users in the form of upvotes, when the code is explained. – Amit Verma Jan 27 '21 at 09:29

Kotlin how to try/catch a cast

3 Answers3