How to idiomatically test for non-null, non-empty strings in Kotlin?

kotlin kotlin-null-safety
iForests picture iForests · Dec 15, 2016 · Viewed 13.2k times · Source

I am new to Kotlin, and I am looking for help in rewriting the following code to be more elegant.

var s: String? = "abc"
if (s != null && s.isNotEmpty()) {
    // Do something
}

If I use the following code:

if (s?.isNotEmpty()) {

The compiler will complain that

Required: Boolean
Found: Boolean?

Thanks.

Answer

miensol picture miensol · Dec 15, 2016

You can use isNullOrEmpty or its friend isNullOrBlank like so:

if(!s.isNullOrEmpty()){
    // s is not empty
}

Both isNullOrEmpty and isNullOrBlank are extension methods on CharSequence? thus you can use them safely with null. Alternatively turn null into false like so:

if(s?.isNotEmpty() ?: false){
    // s is not empty
}

you can also do the following 

if(s?.isNotEmpty() == true){ 
    // s is not empty
}

Related questions

Best way to null check in Kotlin?

Should I use double =, or triple =? if(a === null) { //do something } or if(a == null) { //do something } Similarly for 'not equals': if(a !== null) { //do something } or if(a != null) { //do something }

Read More
What is the Kotlin double-bang (!!) operator?

I'm converting Java to Kotlin with Android Studio. I get double bang after the instance variable. What is the double bang and more importantly where is this documented? mMap!!.addMarker(MarkerOptions().position(london).title("Marker in London"))

Read More
Idiomatic way of handling nullable or empty List in Kotlin

Say I have a variable activities of type List<Any>?. If the list is not null and not empty, I want to do something, otherwise I want to do something else. I came up with following solution: when { …

Read More