Please check the confirmation dialog on your device. What does this mean? I don't want to continue in the course until i figure this out. So I'm not altogether sure why this was happening, but when I ran my app using debug mode, it pointed out that requestFeature must be called before adding content.
I believe it was like this in the video, but for some reason this didnt work for me. So I googled it. Thanks to stackoverflow, i simply put the requestWindowFeature above the super. My version was doing the exact same thing and i did not know why, until now :. Posting to the forum is only allowed for members with active accounts.
To avoid null pointer exceptions, you need to make sure that the object references you're working with are non-null before calling methods on them or trying to access their members. If the object reference is null, handle this case well for example, exit from a method before performing any operations on the object reference and write information to a debug log.
Because you don't want to have null checks for every parameter of every method called, you can rely on the IDE or on the type of the object to signify nullability. Annotate your methods' parameters and return values with Nullable and NonNull to receive compile time warnings from the IDE. These warnings prompt you to expect a nullable object:. These null checks are for objects that you know could be null.
An exception on a NonNull object is an indication of an error in your code that needs to be addressed. Because nullability should be meaningful, you can embed it in the types you use so that there is a compile time check for null.
If you know an object can be null and that nullability should be handled, you could wrap it in an object like Optional. You should always prefer types that convey nullability. In Kotlin, nullability is part of the type system. For example, a variable needs to be declared from the beginning as nullable or non-nullable.
Nullable types are marked with a? Non-nullable variables cannot be assigned a null value and nullable variables need to be checked for nullability before being used as non-null. If you don't want to check for null explicitly, you can use the?. As a best practice, make sure you address the null case for a nullable object, or your app could get into unexpected states.
If your application won't crash anymore with NullPointerException , you won't know that these errors exist. Due to smart-cast and the null check, the Kotlin compiler knows that the string value is non-null so it allows you to use the reference directly, without the need for the safe call operator. This operator allows you to state "if the object is non-null, return the object; otherwise, return something else". You can still get a NullPointerException in Kotlin.
The following are the most common situations:. Platform types are object declarations coming from Java. These types are specially-treated ; null checks are not as enforced, so the non-null guarantee is the same as in Java.
When you access a platform type reference, Kotlin does not create compile time errors but these references can lead to runtime errors. See the following example from the Kotlin documentation:. Kotlin relies on type inference when a platform value is assigned to a Kotlin variable, or you can define what type to expect. The best way to ensure the correct nullability state of a reference coming from Java is to use nullability annotations for example, Nullable in your Java code.
The Kotlin compiler will represent these references as actual nullable or non-nullable types, not as platform types. Types coming from this SDK, that are used in Kotlin, will be represented as correct nullable or non-nullable types.
Because of Kotlin's type system, we've seen apps have a major reduction in NullPointerException crashes. Content and code samples on this page are subject to the licenses described in the Content License.
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