If reference to a variable is not null, use the value, else use some default value that is not null. 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: https://androidpedia.net/en/knowledge-base/51851505/android-kotlin-findviewbyid-must-not-be-null#answer-0. !.findViewById(R.id.btnYES) Without the two buttons for PageTwoActivity So String? Should we be inflating the custom dialog xml? Null safety is one of the best features of Kotlin. Note that there's no point in optimizing your code when comparing to null explicitly: a == null will be automatically translated to a === null. Kotlin's type system is aimed at eliminating the danger of null references from code, also known as the The Billion Dollar Mistake.One of the most common pitfalls in many programming languages, including Java, is that accessing a member of a null reference will result in a null reference exception. It’s not about thread safety, it’s about null-safety. The Elvis operator will evaluate the left expression and will return it if it’s not null else will evaluate the right side expression. January 31, 2020, at 02:40 AM. Tries to assign a nullable view to a lateinit non-nullable view. anyMatch() method takes a predicate, an expression or a function which returns a boolean value. We have looked at a number of posts and tried a few with no results. Also in Kotlin you do not need findViewById to access the activity's views. Kotlin compiler by default doesn’t allow any types to have a value of null at compile-time. Edit Page Filtering. So I search in youtube and I seen a lot of content which uses Fragment for bottom navigation T_T. We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below 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. I.e. In the above code, there will not be any problem on line 3 because fullName variable is 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. To get started, you’ll need to add the kotlin … The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. 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! java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! println(match.value) // to be println(match.range) // 0..4 val nextMatch = match.next()!! You may have noticed that some of the code you’ve replaced uses !!. The language uses plain old null. 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. java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! In Kotlin, constructors are also functions, so we can use default arguments to specify that the default value of lastName is null. to handle null references. Kotlin supports nullability as part of its type System. 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)!! 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. Let’s start with the representation. Should we be inflating the custom dialog xml? Kotlin Null Safety. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). LINK. Follow. NO name conflicts, So the question is how do we FIX the error? In this article, we’ll be looking at the null safety features built into the Kotlin language. 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. Kotlin provides comprehensive, native handling of nullable fields – no additional libraries are needed. In Kotlin, we can assign default values to arguments in function calls. To do this, we just assign null to lastName. april is the Month object with name April and days 30. 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 ! Hence let is inevitably being understood that it is the replacement of null check e.g. Kotlin tries to provide null-safety even when the variable could be changed from another thread. var variable : CustomClass = CustomClass () variable = null //compilation error As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. You can delete all these: findViewByID() returns a nullable object. It checks it using a null check using != null and isEmpty() method of string. Kotlin has a safe call operator (?.) 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. change this btnYES = findViewById(R.id.btnYES) to this btnYES = findViewById(R.id.btnYES)!! The code below shows both approaches: 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. At a higher level, a Kotlin type fits in either of the two. 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. 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. javascript - Ionic 3: Getting value from PlayStore link, sql server - SQL list account managers with predecessor. import kotlin.test. str1 contains null value and str2 is an empty string. Kotlin provides comprehensive, native handling of nullable fields – no additional libraries are needed. Finally, we are printing the objects that we got from find. Yes, I know that this will hopefully become obsolete in the (near?) Based on this predicate, it will return the first element found or null if no element is found. Each find compares the name and days of the finding object in the predicate. But the syntax could be reduced and is given below. https://typealias.com/guides/java-optionals-and-kotlin-nulls We have looked at a number of posts and tried a few with no results. We have only one April Month object in the list. Otherwise, it returns a null value. It force-casts a nullable variable to a non-null … It also returns from the current function if x is null, so it does more than just only assigning x to y if x is not not null. Elye. The custom dialog has its own xml file In this article, we’ll be looking at the null safety features built into the Kotlin language. In the above code, there will not be any problem on line 3 because fullName variable is not null. Here is the PageTwoActivity code. android - Null pointer Exception - findViewById(), android - findViewById for MenuItem returns null, android - findViewById returns null for EditText, android - Toolbar - findViewbyID returning null. Please note that the right side expression will only be called if the left side expression is null. The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. So, in Kotlin, a normal property can’t hold a null value. python - Most elegant way to assign multiple variables to the same value. !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。 That means You have the ability to declare whether a variable can hold a null value or not. If you are familiar with Java, then must have encountered with NullPointerException and to remove this or in other words, we can say that to safely deal with this NullPointerException, the developers of Kotlin introduced Null safety. Maven Dependency. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. function, otherwise (i.e. As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! In Kotlin, null can form special union types with any other type, making them “nullable” and denoting them with the question mark. That’s Kotlin’s non-null assertion operator. In this way, Kotlin with the help of smart casts and special operators make easy to handle null safely. This might sound same as explicitly checking for a null value. Null safety is one of the best features of Kotlin. { "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. Also in Kotlin you do not need findViewById to access the activity's views. Kotlin Program – example.kt So, in Kotlin, a normal property can’t hold a null value. I am trying to implement bottom navigation with an Activity and use Kotlin. 2. However, the JSON sometimes contains null for those fields. In the above program, instead of using a foreach loop, we convert the array to an IntStream and use its anyMatch() method. Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. As we have a list of objects, we will compare the object properties in the predicate. Filtering is one of the most popular tasks in the collection processing. Returns a list containing only the non-null results of applying the given transform function to each element in the original array. bottomnav FindViewById get null (kotlin) 158. 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). 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. 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. is the union of the type String plus the null. For Kotlin, Nullability is a type. Thought there won’t be null crashes if you are not using !! Note that the value might not be present among the tree’s keys and hence the result of the lookup might return a null value. 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 } this link offers advice but we have no idea where to start The custom dialog has its own xml file For example, a normal property can’t hold a null value and will show a compile error. We have looked at a number of posts and tried a few with no results. if a is not null, it calls the equals(Any?) Asserting Not-Null. if… 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. With the introduction of null safety in Kotlin, everybody now know this special standard function let{...}. 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. Here is the PageTwoActivity code. LINK. Maven Dependency. Asserting Not-Null. If you are familiar with Java, then must have encountered with NullPointerException and to remove this or in other words, we can say that to safely deal with this NullPointerException, the developers of Kotlin introduced Null safety. NO name conflicts, So the question is how do we FIX the error? The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: The default value is used when the argument is omitted. using find () : find () takes one predicate that returns one boolean. 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.. 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. Without the two buttons for PageTwoActivity python - Is there a way to disable saving to checkpoints for Jupyter Notebooks? In Kotlin, there is no additional overhead. on Kotlin? 7 ways to null crash Android Kotlin without using !! 2. Nullability and Nullable Types in Kotlin. 7 is not found. 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. change this internal lateinit var btnYES: Button to this internal lateinit var btnYES: Button? Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. This operator executes any action only when the reference has a non-null value. As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity.