import kotlin.test. In this article, we’ll be looking at the null safety features built into the Kotlin language. 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. change this btnYES = findViewById(R.id.btnYES) to this btnYES = findViewById(R.id.btnYES)!! In the above code, there will not be any problem on line 3 because fullName variable is not null. anyMatch() method takes a predicate, an expression or a function which returns a boolean value. You may have noticed that some of the code you’ve replaced uses !!. It force-casts a nullable variable to a non-null … Yes, I know that this will hopefully become obsolete in the (near?) Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. That’s Kotlin’s non-null assertion operator. 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 } In Kotlin, constructors are also functions, so we can use default arguments to specify that the default value of lastName is null. I.e. 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 ! If there was more code in the function after this line, that code would be skipped if x was null since the function already returned. We have looked at a number of posts and tried a few with no results. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. Kotlin has a safe call operator (?.) java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! Filtering is one of the most popular tasks in the collection processing. 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. 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. In Kotlin, there is no additional overhead. With the introduction of null safety in Kotlin, everybody now know this special standard function let{...}. 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. using find () : find () takes one predicate that returns one boolean. 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. 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. As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. For example, a normal property can’t hold a null value and will show a compile error. 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! To get started, you’ll need to add the kotlin … 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. As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! But the syntax could be reduced and is given below. So String? Without the two buttons for PageTwoActivity Should we be inflating the custom dialog xml? Returns a list containing only the non-null results of applying the given transform function to each element in the original array. In Kotlin, null can form special union types with any other type, making them “nullable” and denoting them with the question mark. this link offers advice but we have no idea where to start 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. import kotlin.test. 2. – still_dreaming_1 Jan 31 at 14:29 LINK. Without the two buttons for PageTwoActivity To do this, we just assign null to lastName. Maven Dependency. Returns a list containing all elements that are not 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. In the above code, there will not be any problem on line 3 because fullName variable is not null. 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. In Kotlin, filtering conditions are defined by predicates – lambda functions that take a collection element and return a boolean value: true means that the given element matches the predicate, false means the opposite.. { "boolField": null, "stringField": null } data class TestObject( val boolField: Boolean = true, val stringField: String = "default" ) The key thing here is that the Kotlin properties are not nullable, but there is a known default value for them. Should we be inflating the custom dialog xml? if… So, in Kotlin, a normal property can’t hold a null value. * fun main(args: Array) { //sampleStart val numbers: List = listOf(1, 2, null, 4) val nonNullNumbers = numbers.filterNotNull() println(nonNullNumbers) // [1, 2, 4] //sampleEnd } 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. NO name conflicts, So the question is how do we FIX the error? var variable : CustomClass = CustomClass () variable = null //compilation error 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. That’s Kotlin’s non-null assertion operator. Asserting Not-Null. Kotlin provides comprehensive, native handling of nullable fields – no additional libraries are needed. 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. Here is the PageTwoActivity code. str1 contains null value and str2 is an empty string. The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: In this way, Kotlin with the help of smart casts and special operators make easy to handle null safely. Also in Kotlin you do not need findViewById to access the activity's views. change this internal lateinit var btnYES: Button to this internal lateinit var btnYES: Button? future, but for now, … Tries to assign a nullable view to a lateinit non-nullable view. No null safety. Elye. this link offers advice but we have no idea where to start Also in Kotlin you do not need findViewById to access the activity's views. Nullability and Nullable Types in Kotlin. The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! Note that there's no point in optimizing your code when comparing to null explicitly: a == null will be automatically translated to a === null. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). !.findViewById(R.id.btnYES) So I search in youtube and I seen a lot of content which uses Fragment for bottom navigation T_T. To get started, you’ll need to add the kotlin … 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 code below shows both approaches: Kotlin tries to provide null-safety even when the variable could be changed from another thread. 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. 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。 bottomnav findViewById get null ( Kotlin ) 158 it using a null value being. 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