How to check if a "lateinit" variable has been initialized?
There is a lateinit
improvement in Kotlin 1.2 that allows to check the initialization state of lateinit
variable directly:
lateinit var file: File
if (this::file.isInitialized) { ... }
See the annoucement on JetBrains blog or the KEEP proposal.
UPDATE: Kotlin 1.2 has been released. You can find lateinit
enhancements here:
- Checking whether a lateinit var is initialized
- Lateinit top-level properties and local variables
You can easily do this by:
::variableName.isInitialized
or
this::variableName.isInitialized
But if you are inside a listener or inner class, do this:
this@OuterClassName::variableName.isInitialized
Note: The above statements work fine if you are writing them in the same file(same class or inner class) where the variable is declared but this will not work if you want to check the variable of other class (which could be a superclass or any other class which is instantiated), for ex:
class Test {
lateinit var str:String
}
And to check if str is initialized:
What we are doing here: checking isInitialized
for field str
of Test
class in Test2
class.
And we get an error backing field of var is not accessible at this point.
Check a question already raised about this.
Using .isInitialized
property one can check initialization state of a lateinit variable.
if (::file.isInitialized) {
// File is initialized
} else {
// File is not initialized
}
Try to use it and you will receive a UninitializedPropertyAccessException
if it is not initialized.
lateinit
is specifically for cases where fields are initialized after construction, but before actual use (a model which most injection frameworks use).
If this is not your use case lateinit
might not be the right choice.
EDIT: Based on what you want to do something like this would work better:
val chosenFile = SimpleObjectProperty<File?>
val button: Button
// Disables the button if chosenFile.get() is null
button.disableProperty.bind(chosenFile.isNull())