A summary of Kotlin tips from #31DaysofKotlin
elvis operator
When you have a nullable type, use the default value if it is not null use the value.
Docs: https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator
string templates
A string template expression starts with a dollar sign $. Evaluate expressions using ${expression}.
Docs: https://kotlinlang.org/docs/reference/basic-types.html#string-templates
Destructuring declarations
Android KTX uses destructuring to assign the component values of a color.
Docs: https://kotlinlang.org/docs/reference/multi-declarations.html
when
when replaces the switch operator. Kotlin’s when expression can match on just about anything.
Docs: https://kotlinlang.org/docs/reference/control-flow.html#when-expression
ranges
For loops, range expressions
Docs : https://kotlinlang.org/docs/reference/ranges.html
properties
In Kotlin, classes can have mutable and read-only properties, with getters and setters generated by default. You can also implement custom ones
Docs : https://kotlinlang.org/docs/reference/properties.html
data classes : one role: to hold data.
The default implementation of equals() is generated (so are hashCode(), toString(), and copy()) and checks for structural equality.
Docs : https://kotlinlang.org/docs/reference/data-classes.html
access modifiers
Kotlin has a rich set of visibility modifiers you can use as well: private, protected, internal.
Docs : https://kotlinlang.org/docs/reference/visibility-modifiers.html
default parameters
Is the number of method overloads getting out of hand? Specify default parameter values in functions. Make the code even more readable with named parameters.
Docs : https://kotlinlang.org/docs/reference/functions.html#default-arguments
sealed classes
Kotlin sealed classes let you easily handle error data.
They’re a perfect fit for ViewHolders.
RecyclerView and detail clicks, shares, delete actions and etc.
Docs : https://kotlinlang.org/docs/reference/sealed-classes.html
lazy
Defer the cost of expensive property initialization until they’re actually needed
Docs : https://kotlinlang.org/docs/reference/delegated-properties.html#lazy
lateinit
In Kotlin non-null vals must be initialized. What to do? It’s a promise: initialize me later!
Docs : https://kotlinlang.org/docs/reference/properties.html#late-initialized-properties-and-variables
require
Are your function arguments valid? Check before using them, with require. If they’re not valid an IllegalArgumentException is thrown.
Docs : https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/require.html
inline
Can’t wait to use lambdas to make new APIs? Get in line. Kotlin lets you specify a function as inline — which means calls will be replaced with the function body. Breathe and make lambda-based APIs with zero overhead.
Docs : https://kotlinlang.org/docs/reference/inline-functions.html
operator overloading
Write Kotlin (time * 2) faster with operator overloading. Objects like Path, Range or SpannableStrings naturally allow for operations like addition or subtraction.
Docs : https://kotlinlang.org/docs/reference/operator-overloading.html#operator-overloading
basic syntax
Utility methods for a class? Add them to the top level of the source file. In Java, they are compiled as static methods of that class
Docs : https://kotlinlang.org/docs/reference/basic-syntax.html
Iterating types without an iterator
Iterators in interesting places? Android KTX adds iterators to ViewGroup and SparseArray. To define iterator extensions use the operator keyword. Foreach loops will use the extensions!
Docs :https://github.com/android/android-ktx/blob/master/src/main/java/androidx/core/view/ViewGroup.kt#L66
easy content values
Combine the power of ContentValues with the brevity of Kotlin. Use the Android KTX ContentValues creator and just pass a Pair<StringKey, Value>. Android KTX implementation.
bundles
Bundle creator in Android KTX. No more calls to putString, putInt, or any of their 20 friends. One call will make you a new Bundle
Docs : https://github.com/android/android-ktx/blob/master/src/main/java/androidx/core/os/Bundle.kt#L27
cleaning up postDelayed
Lambdas are sweet. With last parameter call syntax, you can cleanup callbacks, Callable, and Runnable. Example from Android KTX.
Docs :https://github.com/android/android-ktx/blob/master/src/main/java/androidx/core/os/Handler.kt#L38
@file:JvmName
Using Kotlin and Java in the same project? Do you have classes with top-level functions or properties? By default, the compiler generates the class name as YourFileKt. Change it by annotating the file with @file:JvmName.
Docs :https://kotlinlang.org/docs/reference/java-to-kotlin-interop.html#package-level-functions
One plus : Statics, @JvmStatic
by
Delegate your work to another class with by.
Docs :https://kotlinlang.org/docs/reference/delegation.html#implementation-by-delegation
extension functions
No more Util classes! Extend the functionality of a class by using extension functions. Put the name of the class you’re extending before the name of the method you’re adding.
KTX Graphics
Android KTX has a great set of functions to make your code more concise when working with classes from the graphics package.
spans
Android KTX adds extension functions for some of the most common spans and makes the API easier to use.
parcelize
Love the speed of Parcelable, but don’t like writing all that code? Say hello to @Parcelize.
KTX view padding
Android KTX lets you set the padding on one side of a view using default parameters.
Docs : https://github.com/android/android-ktx/blob/master/src/main/java/androidx/core/view/View.kt#L117
Disclaimer :
All the content of these example codes and some descriptions are taken from Android Developers twitter account.
