The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. With the introduction of null safety in Kotlin, everybody now know this special standard function let{...}. Let’s start with the representation. String { if (name.isNullOrBlank()) throw IllegalArgumentException("Name cannot be blank") // name is not nullable here anymore due to a smart cast after calling isNullOrBlank return name } println(validateName("Adam")) // Adam // validateName(null) // will fail // validateName("") // will fail // validateName(" \t\n") // will fail //sampleEnd } Finally, we are printing the objects that we got from find. This might sound same as explicitly checking for a null value. This operator executes any action only when the reference has a non-null value. We have looked at a number of posts and tried a few with no results. The takeaway here is that null is not necessarily your only choice as a default value, ... Kotlin is but a tool, and a powerful one that is, but how you use that tool can make a world of difference. It force-casts a nullable variable to a non-null … !.findViewById(R.id.btnYES) As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! Based on this predicate, it will return the first element found or null if no element is found. You can delete all these: One approach that you can take is instead of trying to customize the Dialog by using setContentView, you can extend DialogFragment with a new Custom Dialog Fragment. In this article, we’ll be looking at the null safety features built into the Kotlin language. Kotlin has a safe call operator (?.) import kotlin.test. Without the two buttons for PageTwoActivity this link offers advice but we have no idea where to start NO name conflicts, So the question is how do we FIX the error? You may have noticed that some of the code you’ve replaced uses !!. It force-casts a nullable variable to a non-null … In Android Studio 4.1+, when you create a new Kotlin project and try to connect an XML layout file with your .kt file using Kotlinx synthetic, you’ll see you can’t do it anymore. Yes, I know that this will hopefully become obsolete in the (near?) anyMatch() method takes a predicate, an expression or a function which returns a boolean value. In Kotlin, there is no additional overhead. We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below No null safety. You may have noticed that some of the code you’ve replaced uses !!. The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: Then you can approach it similar to how you would a fragment; You inflate a view in onCreateDialog, this is an approach I found in a similar question: Licensed under cc by-sa 3.0 with attribution required. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. is the union of the type String plus the null. Kotlin supports nullability as part of its type System. To get started, you’ll need to add the kotlin … 7 is not found. Asserting Not-Null. a is null) it checks that b is referentially equal to null. The code below shows both approaches: 7 ways to null crash Android Kotlin without using !! That means You have the ability to declare whether a variable can hold a null value or not. Android Kotlin findViewById must not be null We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below java.lang.IllegalStateException: findViewById (R.id.btnYES) must not be null The error source is eluding us ! The Elvis operator will evaluate the left expression and will return it if it’s not null else will evaluate the right side expression. If reference to a variable is not null, use the value, else use some default value that is not null. Optional usage requires creating a new object for the wrapper every time some value is wrapped or transformed to another type — with the exclusion of when the Optional is empty (singleton empty Optional is used). function, otherwise (i.e. The default value is used when the argument is omitted. In Java this would be the equivalent of a NullPointerException or NPE for short.Kotlin's type system is aimed to eliminate NullPointerException's from our code. Thought there won’t be null crashes if you are not using !! I am trying to implement bottom navigation with an Activity and use Kotlin. To get started, you’ll need to add the kotlin … In the above code, there will not be any problem on line 3 because fullName variable is not null. if a is not null, it calls the equals(Any?) So, in Kotlin, a normal property can’t hold a null value. Kotlin Android Extensions are another Kotlin plugin that is included in the regular one, and that will allow recovering views from Activities, Fragments, and Views in an amazing seamless way. If you checked your local variable and it’s not null, nothing in the world could make it null, so Kotlin compiler allows to treat is as a non-null value. Kotlin compiler by default doesn’t allow any types to have a value of null at compile-time. So next time you declare a variable in your code, don’t rush to add that little question mark and ask yourself the important questions. change this internal lateinit var btnYES: Button to this internal lateinit var btnYES: Button? The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: Also in Kotlin you do not need findViewById to access the activity's views. – still_dreaming_1 Jan 31 at 14:29 Kotlin Program – example.kt Kotlin Android Extensions are another Kotlin plugin that is included in the regular one, and that will allow recovering views from Activities, Fragments, and Views in an amazing seamless way. 2. For example, a normal property can’t hold a null value and will show a compile error. NO name conflicts, So the question is how do we FIX the error? Should we be inflating the custom dialog xml? That’s Kotlin’s non-null assertion operator. 2. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. The custom dialog has its own xml file In Kotlin, constructors are also functions, so we can use default arguments to specify that the default value of lastName is null. The language uses plain old null. !なんてやっちゃったら、場合によっては落ちます。 ただKotlinにはJavaにはないスコープ関数や拡張関数、エルビス演算子などがあります。 fun main(args: Array) { //sampleStart val inputString = "to be or not to be" val regex = "to \\w{2}".toRegex() // If there is matching string, then find method returns non-null MatchResult val match = regex.find(inputString)!! Kotlin tries to provide null-safety even when the variable could be changed from another thread. this link offers advice but we have no idea where to start In the above code, there will not be any problem on line 3 because fullName variable is not null. To do this, we just assign null to lastName. The custom dialog has its own xml file bottomnav FindViewById get null (kotlin) 158. Follow. Null safety is one of the best features of Kotlin. We have only one April Month object in the list. Without the two buttons for PageTwoActivity It’s not about thread safety, it’s about null-safety. You can delete all these: findViewByID() returns a nullable object. Nullability and Nullable Types in Kotlin. Tries to assign a nullable view to a lateinit non-nullable view. kotlin.internal.InlineOnly public inline fun CharSequence?.isNotEmpty(): Boolean = this != null && length > 0 This would be more comprehensive, so … One approach that you can take is instead of trying to customize the Dialog by using setContentView, you can extend DialogFragment with a new Custom Dialog Fragment. We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). KotlinはNull安全なプログラム言語だといいますが、当然ながらNullを取りうる変数objに対して、obj! Hence let is inevitably being understood that it is the replacement of null check e.g. java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. So, in Kotlin, a normal property can’t hold a null value. Note, how we have used the Kotlin keyword when which is a Java analog of the switch-case statement but much more powerful and flexible. Here is the PageTwoActivity code. Maven Dependency. Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. Fragment for bottom navigation T_T, there will not be any problem on 3. 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