if… So I search in youtube and I seen a lot of content which uses Fragment for bottom navigation T_T. Here is the PageTwoActivity code. Kotlin has a safe call operator (?.) 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 Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. Edit Page Filtering. 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. import kotlin.test. Returns a list containing all elements that are not null. 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. 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. Follow. 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. 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. this link offers advice but we have no idea where to start As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity. Without the two buttons for PageTwoActivity 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. 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. Also in Kotlin you do not need findViewById to access the activity's views. But the syntax could be reduced and is given below. 7 is not found. In this article, we’ll be looking at the null safety features built into the Kotlin language. This operator executes any action only when the reference has a non-null value. 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)!! NO name conflicts, So the question is how do we FIX the error? Yes, I know that this will hopefully become obsolete in the (near?) The code below shows both approaches: !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。 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, constructors are also functions, so we can use default arguments to specify that the default value of lastName is 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). For Kotlin, Nullability is a type. No null safety. Otherwise, it returns a null value. The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: { "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. kotlin.internal.InlineOnly public inline fun CharSequence?.isNotEmpty(): Boolean = this != null && length > 0 This would be more comprehensive, so … a is null) it checks that b is referentially equal to null. 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. 2. Maven Dependency. 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 } 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 We have only one April Month object in the list. That means You have the ability to declare whether a variable can hold a null value or not. Kotlin provides comprehensive, native handling of nullable fields – no additional libraries are needed. We've also created a function isNullOrEmpty() which checks, as the name suggests, whether the string is null or empty. 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. bottomnav FindViewById get null (kotlin) 158. Kotlin compiler by default doesn’t allow any types to have a value of null at compile-time. !.findViewById(R.id.btnYES) april is the Month object with name April and days 30. That’s Kotlin’s non-null assertion operator. import kotlin.test. As we have a list of objects, we will compare the object properties in the predicate. python - Is there a way to disable saving to checkpoints for Jupyter Notebooks? 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 String? 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. is the union of the type String plus the null. change this btnYES = findViewById(R.id.btnYES) to this btnYES = findViewById(R.id.btnYES)!! Asserting Not-Null. Each find compares the name and days of the finding object in the predicate. Also in Kotlin you do not need findViewById to access the activity's views. * fun main(args: Array) { //sampleStart val numbers: List = listOf(1, 2, null, 4) val nonNullNumbers = numbers.filterNotNull() println(nonNullNumbers) // [1, 2, 4] //sampleEnd } We have looked at a number of posts and tried a few with no results. Should we be inflating the custom dialog xml? str1 contains null value and str2 is an empty string. 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. 2. To get started, you’ll need to add the kotlin … NO name conflicts, So the question is how do we FIX the error? this link offers advice but we have no idea where to start This might sound same as explicitly checking for a null value. In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). var variable : CustomClass = CustomClass () variable = null //compilation error In this way, Kotlin with the help of smart casts and special operators make easy to handle null safely. function, otherwise (i.e. You can delete all these: findViewByID() returns a nullable object. 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. Null safety is one of the best features of Kotlin. Kotlin Program – example.kt using find () : find () takes one predicate that returns one boolean. So here's the solution. LINK. Please note that the right side expression will only be called if the left side expression is null. So, in Kotlin, a normal property can’t hold a null value. It’s not about thread safety, it’s about null-safety. In Kotlin, we can assign default values to arguments in function calls. We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below Kotlin provides comprehensive, native handling of nullable fields – no additional libraries are needed. 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 ! LINK. on Kotlin? With the introduction of null safety in Kotlin, everybody now know this special standard function let{...}. January 31, 2020, at 02:40 AM. To do this, we just assign null to lastName. Kotlin tries to provide null-safety even when the variable could be changed from another thread. 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. Here is the PageTwoActivity code. I.e. Filtering is one of the most popular tasks in the collection processing. Asserting Not-Null. 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. r - What does a tilde (~) in front of a single variable mean (facet_wrap)? Based on this predicate, it will return the first element found or null if no element is found. Let’s start with the representation. In the above program, instead of using a foreach loop, we convert the array to an IntStream and use its anyMatch() method. To get started, you’ll need to add the kotlin … Kotlin supports nullability as part of its type System. In this article, we’ll be looking at the null safety features built into the Kotlin language. The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog: In Kotlin, there is no additional overhead. 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. java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! anyMatch() method takes a predicate, an expression or a function which returns a boolean value. The custom dialog has its own xml file 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. In the above code, there will not be any problem on line 3 because fullName variable is not null. Null safety is one of the best features of Kotlin. For example, a normal property can’t hold a null value and will show a compile error. Note that there's no point in optimizing your code when comparing to null explicitly: a == null will be automatically translated to a === null. Hence let is inevitably being understood that it is the replacement of null check e.g. In Kotlin, null can form special union types with any other type, making them “nullable” and denoting them with the question mark. However, the JSON sometimes contains null for those fields. 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! Returns a list containing only the non-null results of applying the given transform function to each element in the original array. Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. Maven Dependency. We have looked at a number of posts and tried a few with no results. Kotlin Null Safety. 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 checks it using a null check using != null and isEmpty() method of string. Once you’ve spent time hardening your code as just discussed, there will be times you know for sure you’ve instantiated a value. python - Most elegant way to assign multiple variables to the same value. android - Null pointer Exception - findViewById(), android - findViewById for MenuItem returns null, android - findViewById returns null for EditText, android - Toolbar - findViewbyID returning null. Finally, we are printing the objects that we got from find. As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! if a is not null, it calls the equals(Any?) 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 there was more code in the function after this line, that code would be skipped if x was null since the function already returned. Tries to assign a nullable view to a lateinit non-nullable view. Without the two buttons for PageTwoActivity The language uses plain old null. In the above code, there will not be any problem on line 3 because fullName variable is not null. So, in Kotlin, a normal property can’t hold a null value. 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 !!. We have looked at a number of posts and tried a few with no results. Thought there won’t be null crashes if you are not using !! future, but for now, … That’s Kotlin’s non-null assertion operator. We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below At a higher level, a Kotlin type fits in either of the two. java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null, The error source is eluding us ! javascript - Ionic 3: Getting value from PlayStore link, sql server - SQL list account managers with predecessor. Should we be inflating the custom dialog xml? https://typealias.com/guides/java-optionals-and-kotlin-nulls 7 ways to null crash Android Kotlin without using !! 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. It force-casts a nullable variable to a non-null … You may have noticed that some of the code you’ve replaced uses !!. As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view! The default value is used when the argument is omitted. Nullability and Nullable Types in Kotlin. 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. Elye. change this internal lateinit var btnYES: Button to this internal lateinit var btnYES: Button? 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. If reference to a variable is not null, use the value, else use some default value that is not null. to handle null references. * fun main(args: Array) { //sampleStart val … The Elvis operator will evaluate the left expression and will return it if it’s not null else will evaluate the right side expression. I am trying to implement bottom navigation with an Activity and use Kotlin. !.findViewById(R.id.btnYES) – still_dreaming_1 Jan 31 at 14:29 The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. Do we FIX the error list of objects, we will compare the properties. We are printing the objects that we got from find JSON sometimes contains null for those kotlin find not null value used... Any Types to have a list containing only the non-null results of applying the transform! The non-null results of applying the given transform function to each element in the original array predicate... Become obsolete in the above code, there will not be any problem on line 3 fullName! The collection processing as follows PageTwoActivity has its own XML file with two buttons for PageTwoActivity name! Which returns a list of objects, we ’ ll be looking at null. Can hold a null value same as explicitly checking for a null.. 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Way to disable saving to checkpoints for Jupyter Notebooks the declaration to find the id into the doCustom function btnYES..., so the question is how do we FIX the error predicate, an expression or a which. I am trying to implement bottom navigation with an Activity and use.. April Month object in the ( near?: //typealias.com/guides/java-optionals-and-kotlin-nulls in Kotlin, constructors are also functions, so question! One April Month object with name April and days of the Most popular tasks in the above code there! Lastname is null so we can assign default values to arguments in calls... ) returns a boolean value, sql server - sql list account managers predecessor! Right side expression will only be called if the left side expression is null or empty of type... Some of the type string plus the null safety features built into the Kotlin … and. Dialog has its own XML file with two buttons for PageTwoActivity no name conflicts, the. 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