android
[dev-todo-mvvm-live-kotlin] App crashes when adding task with empty title or description
saveTask() function of AddEditTaskViewModel.kt is calling Task(title.get(), description.get()) which causes crash when adding new task with title or description being empty.
the crash happens because in the dev-todo-mvvm-live-kotlin branch the ViewModel’s saveTask() is doing something like:
fun saveTask() { val task = Task(title.get(), description.get()) // <- boom if null ... } Here, title and description are probably ObservableField<String> values bound to EditTexts. If the user hasn’t typed anything, get() returns null, which violates Task’s constructor requirements (likely non-null String) and leads to a NullPointerException.
Why it crashes In Kotlin, if Task’s constructor is defined as:
data class Task( val title: String, val description: String, ... ) then passing a null from title.get() or description.get() will crash at runtime because Kotlin’s non-null parameters can’t be null.
How to fix it The fix is to handle null or empty cases before constructing the Task.
Option 1 – Use default empty strings
fun saveTask() { val currentTitle = title.get()?.trim().orEmpty() val currentDescription = description.get()?.trim().orEmpty()
if (currentTitle.isEmpty() && currentDescription.isEmpty()) {
// Show an error message via LiveData
_snackbarText.value = R.string.empty_task_message
return
}
val task = Task(currentTitle, currentDescription)
...
} Option 2 – Prevent saving empty tasks altogether If the app shouldn’t allow empty titles or descriptions:
fun saveTask() { val currentTitle = title.get()?.trim() val currentDescription = description.get()?.trim()
if (currentTitle.isNullOrEmpty() || currentDescription.isNullOrEmpty()) {
_snackbarText.value = R.string.empty_task_message
return
}
val task = Task(currentTitle, currentDescription)
...
} Option 3 – Change Task to accept nullable values Not really recommended here, because the Task model should represent a valid, saved entity, not a partially empty one.
Why the original code didn’t guard against null The original MVVM sample assumes the binding layer or XML input validation ensures non-null values, but in practice, data binding ObservableField can still be null unless you initialize it and trim input before use.
