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Basics of Jetpack Compose in Android
  • Last Updated : 25 Feb, 2021

Jetpack Compose is a modern UI toolkit that is designed to simplify UI development in Android. It consists of a reactive programming model with conciseness and ease of Kotlin programming language. It is fully declarative so that you can describe your UI by calling some series of functions that will transform your data into a UI hierarchy. When the data changes or is updated then the framework automatically recalls these functions and updates the view for you. In this article, we will see some of the basic topics which are helpful before starting with Jetpack Compose.

  • What is Jetpack Compose?
  • What are its benefits?
  • What challenges we can solve by using Jetpack Compose?
  • Some basic functions of Jetpack compose.

What is Jetpack Compose? 

Jetpack Compose is a modern UI toolkit recently launched by Google which is used for building native Android UI. It simplifies and accelerates the UI development with less code, Kotlin APIs, and powerful tools. 

What are the Benefits of Using Jetpack Compose? 

  • Declarative: It is fully declarative so that you can describe your UI components by calling some predefined functions.
  • Compatible: It is easily compatible with the existing views present in Android. 
  • Increase development speed: Previously developers have to work on the XML file and Kotlin file. But with the help of jetpack compose this becomes easy and developers only have to work on Kotlin file that’s why it will help developers in increasing development speed. 
  • Concise and Idiomatic Kotlin: Jetpack compose built the UI with the benefit that Kotlin brings. 
  • Easy to maintain: As the codebase of any application is present in a single file. It becomes easy to manage and handle the codebase of the application.
  • Written in Kotlin: The application written using jetpack compose uses 100 % of Kotlin programming language. 

What challenges we can solve using Jetpack Compose? 

  • When writing our code we create multiple methods for different purposes. After that we couple this method in our main function according to our requirement. In Android when building any type of view and setting data to that particular view. First of all, we initialize that view with a variable and then add data to that specific view. This process of coupling UI elements with the View Model is called Coupling. When our code is having so many couplings it becomes difficult to maintain this code. So coupling can give you sometimes some Null Reference errors. 
  • While developing apps in Java we generally prefer using View Modal concept in which we find each view from our XML layout file inside our Java class and add data to that specific view according to our requirement. In most apps, we use the UI elements to display dynamically so this may sometimes give you an error of NullRefrence. In this method, UI elements are declared in XML language whereas the functionality is written in java or Kotlin and we link UI elements with our Java or Kotlin class with the findViewbyId() method.  
  • If we will prefer to use the same language for writing our UI components and for adding the functionality it will become easier to maintain our code. By using this method the number of couplings inside our code will also reduce.  

Some Basic Functions of Jetpack Compose

  1. Composable Function: Composable Function is represented in code by using @Composable annotation to the function name. This function will let you define your app’s UI programmatically by describing its shape and data dependencies rather than focusing on the UI construction process. 
  2. Preview Function: The name of the function itself tells us that the function is used to generate the preview of the composable function. It is used to display a preview of our composable functions within our IDE rather than installing our APK in an emulator or a virtual device. The preview function is annotated by @Preview. 
  3. Column Function: The column function is used to stack UI elements in a vertical manner. This function will stack all the children directly one after another in a vertical manner with no spacing between them. It is annotated with Column().
  4. Row Function: The row function is used to stack UI elements in a horizontal manner. This function will stack all the children one after the other in a horizontal manner with no spacing between them. It is annotated with Row()
  5. Stack: A widget that is used to positioned elements one over the another. It will position its children relative to its edges. The stack is used to draw the children which will overlap in the order that they are specified. It is annotated with Stack().
  6. Fixed Spacer: It is used to give spacing between two views. We can specify the height and width of the box. It is an empty box that is used to give spacing between the views. It is annotated with FixedSpacer()
  7. Vertical Scroller: If the UI components inside the app do not fit the height of the screen then we have to use the scrolling type of view. With the help of a vertical scroller, we can provide a vertically scrolling behavior to our view. The contents inside the vertical scroller will be clipped to the bounds of the vertical scroller. It is annotated with VerticalScroller().
  8. Padding: The padding function is used to provide extra white space according to the requirement around the specific view. It is simply annotated with Padding()
  9. Container: A container is also referred to as a parent widget which combines all common layout widgets for one child such as padding, alignment, width, height, and many more. It is annotated with Container()
  10. Center: A layout that takes a child and centers it within itself. The layout will be as large as possible with finite incoming constraints or wrap content otherwise. It is annotated with Center()
  11. Constrained Box: It is a widget that will constraints its only child. The Constrained box will itself create a layout that will take the same size as that of the child chooses. It is annotated with ConstrainedBox()
  12. Flex Column: It is a widget that will place its children in a vertical sequence assigning the width of children according to their flex weights. It is annotated with FlexColumn().  
  13. Flex Row: It is a widget that will place its children in a horizontal sequence assigning the width of children according to their flex weights. It is annotated with FlexRow()
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