Lazy Car Android
Alfonzo Liebenstein
lazy() is a function that takes a lambda and returns an instance of Lazy which can serve as a delegate for implementing a lazy property: the first call to get() executes the lambda passed to lazy() and remembers the result, subsequent calls to get() simply return the remembered result.
lateinit var has a backing field which stores the value, and by lazy ... creates a delegate object in which the value is stored once calculated, stores the reference to the delegate instance in the class object and generates the getter for the property that works with the delegate instance. So if you need the backing field present in the class, use lateinit;
lateinit var can be initialized from anywhere the object is seen from, e.g. from inside a framework code, and multiple initialization scenarios are possible for different objects of a single class. by lazy ... , in turn, defines the only initializer for the property, which can be altered only by overriding the property in a subclass. If you want your property to be initialized from outside in a way probably unknown beforehand, use lateinit.
Initialization by lazy ... is thread-safe by default and guarantees that the initializer is invoked at most once (but this can be altered by using another lazy overload). In the case of lateinit var, it's up to the user's code to initialize the property correctly in multi-threaded environments.
A lambda passed to by lazy ... may capture references from the context where it is used into its closure.. It will then store the references and release them only once the property has been initialized. This may lead to object hierarchies, such as Android activities, not being released for too long (or ever, if the property remains accessible and is never accessed), so you should be careful about what you use inside the initializer lambda.
But lateinit is used when you are sure a variable won't be null or empty and will be initialized before you use it -e.g. in onResume() method for android- and so you don't want to declare it as a nullable type.
Everything is correct above, but one of facts simple explanation LAZY----There are cases when you want to delay the creation of an instance of your object until itsfirst usage. This technique is known as lazy initialization or lazy instantiation. The mainpurpose of lazy initialization is to boost performance and reduce your memory footprint. Ifinstantiating an instance of your type carries a large computational cost and the programmight end up not actually using it, you would want to delay or even avoid wasting CPUcycles.
Need an introduction to Kotlin? Download our free eBook to learn what this language means for your Android App.LazyA property defined via by lazy is initialized using the supplied lambda upon first use, unless a value had been previously assigned.
Unlike other languages, lazy in Kotlin is not a language feature, but a property delegate implemented in the standard library. Thus, it is possible to draw on it as inspiration and perform a mind experiment. Would it be possible to resolve the memory leak and the lack of lifecycle-awareness of the by lazy approach?
Do you have properties in your Kotlin types that you want to create later after initialization? You may want to avoid making them nullable, avoid using lateinit or delay an expensive set up process to a later point. In Kotlin this is where delegated properties and lazy properties in particular can be used, allowing properties to be initialized when they are needed and even keep our main type's initialization simpler and cleaner.
The idea of making a property lazy is not new to Kotlin and many developers having been doing it in other languages or doing it themselves for ages. There were common approaches to a form of lazy creation in Java, it was hard to live in the Java world without coming across a getInstance() function at some point!
When it comes to defining lazy properties in Kotlin, they have been brought into being part of the language. There is some new syntax, some different options for initializing them and various situations in which they can be really useful. Let's take a look!
Creating a lazy property in Kotlin is pretty simple, we define it using by lazy and provide a function initializer. At a later point, when the property is first accessed it will be initialized using the function we provided and then on future accesses the cached value will be returned instead. Nifty!
Our bindingController property needs to access the viewModel property in order to be created and so by making it lazy, this can be deferred until it is first used. After bindingController has been initialized, the value will simply be returned every time from then on.
Creating our property may not always be as simple as just calling an initializer and more code may be needed to set it up. In these situations we may wish to move the contents of the lazy function initializer to a factory method on the outer class.
Across our codebase there will be common situations for using lazy properties and so to simplify the call sites we may decide to use an extension function. For example, when using Android ViewModel, each of our Activities will need to retrieve their View Model, which can be done using an extension function on a common base class.
In the case of by lazy, a Lazy delegate type will control access to our property, initializing it on first access and then returning the cached value on subsequent accesses. Users of the property don't need to change how they call it, meaning the read-write behaviour of our property can be changed at the property definition without affecting code that uses it.
The lazy function has an argument with a default value that controls its synchronization behaviour. If a lazy property is accessed from multiple threads concurrently, synchronization will need to be handled by choosing an appropriate LazyThreadSafetyMode.
When we just want to delay initialization, lazy can be a nicer approach to the alternatives. It can be especially helpful for obtaining dependencies whose initialization is out of our control, such as Android View Models from an Activity or Fragment.
There are times when we need to read a value from somewhere, but don't want it to be retrieved again each time it is needed. An example is reading Bundle extras from an Intent, where using a lazy property would mean on first access the value is read from the Intent and then cached for quicker access in the future.
Delegated properties and lazy properties in particular are a great feature to have at our disposal. The give us flexibility over how our properties are initialized and accessed. It is really nice to be able to make a property lazy without having to alter how it is used in calling code.
Aside from this, TV composables have TV-specific APIs that hide properties that are not relevant on TV devices (e.g flingBehaviour), and expose properties that specific to TV experiences (e.g pivotOffsets). The composables will also allow us to ensure that TV-specific behaviours are automatically applied in our apps (such as focus management or navigation), as the standard lazy composables may not always have awareness of these concepts. With the exposed APIs being almost identical, there is not extra overhead in utilising these TV-specific composables.
We have seen how simple it is to convert an eagerly evaluated method into a lazy evaluated one. Although the lazy call is a bit more involved compared to the eager call, the performance gains payoff the cosmetic drawback. Having said that, do not use lazy strategy everywhere, but do use it for cases where there are clear signs of performance improvements, i.e. :
We recorded episode 191 from thestudio in the London office, where Rebecca Franks from thedeveloper relations team joined Chet as a guest host. We talkedwith Andrei Shikov, Matvei Malkov, and Andrey Kulikov from theJetpack Compose engineering team about layouts, especially the lazyones, which are the Compose equivalent of RecyclerView.
You can let lombok generate a getter which will calculate a value once, the first time this getter is called, and cache it from then on. This can be useful if calculating the value takes a lot of CPU, or the value takes a lot of memory. To use this feature, create a private final variable, initialize it with the expression that's expensive to run, and annotate your field with @Getter(lazy=true). The field will be hidden from the rest of your code, and the expression will be evaluated no more than once, when the getter is first called. There are no magic marker values (i.e. even if the result of your expensive calculation is null, the result is cached) and your expensive calculation need not be thread-safe, as lombok takes care of locking.
To overcome this situation with Reflection, Joshua Bloch suggests the use of enum to implement the singleton design pattern as Java ensures that any enum value is instantiated only once in a Java program. Since Java Enum values are globally accessible, so is the singleton. The drawback is that the enum type is somewhat inflexible (for example, it does not allow lazy initialization).
The queried comment is used to lazy load its post. The author of the post is lazy loaded from the post. All of the comments for the post are lazy loaded as allCommentsForPost. For each comment, the author is loaded as commentAuthor. If there are more comments to load, hasNextPage() returns true and getNextPage() loads the next page from the underlying data source.
If the model types have been replaced with the latest codegen for lazy loading, the same mutation will no longer include the post fields, causing the subscription in the previous app to fail decoding the response payload. To make sure the new version of the app works with previous versions, include the @belongsTo and @hasOne connected models in the selection set using the includes parameter of your mutation request.
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