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Mohit Sarveiya Introduction to Jetpack Compose @heyitsmohit

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Introduction to Jetpack Compose ● Thinking in Compose ● Layouts ● Managing State ● Side Effects

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Thinking in Compose

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Imperative

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Imperative 
 
 
 
 ConstraintLayout>

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Imperative View View Group

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Imperative val textView = findViewById(R.id.textView)

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Imperative val textView = findViewById(R.id.textView) textView.text = ...

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Declarative UI ● Widgets are stateless ● No getters or setters to update state

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What is Jetpack Compose UI? ● UI toolkit ● Declarative UI framework

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Benefits ● Faster development ● Build UIs with less code

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Declarative UI Hello Mike

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Declarative UI Hello Mike @Composable fun GreetingView(name: String) { }

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Declarative UI Hello Mike @Composable fun GreetingView(name: String) { Text(text = "Hello $name") }

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Declarative UI Hello Mike class MainActivity { setContent { 
 GreetingView(name = “Mike") 
 } }

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Declarative UI Hello Mike Update state?

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Declarative UI Hello Bill GreetingView(name = “Bill”)

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Recomposition Event Composable UI-Redraw

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Recomposition Event Composable UI-Redraw

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Recomposition Event Composable UI-Redraw

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Modifiers

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Modifiers Hello World Text( modifier = Modifier .padding(10.dp), text = "Hello World" )

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Modifiers Hello World Text( modifier = Modifier .background(Color.Green), text = "Hello World" )

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Modifiers Hello World Text( modifier = Modifier .border(width = 2.dp, Color.Green), text = "Hello World" )

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Modifiers ● Order matters

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Modifiers Hello World Text( modifier = Modifier .border(width = 2.dp, Color.Red) .background(Color.Green) .padding(12.dp), text = "Hello World" )

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Modifiers Hello World Text( modifier = Modifier .padding(12.dp) .border(width = 2.dp, Color.Red) .background(Color.Green), text = "Hello World” )

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No content

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Layouts

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Column

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Column Column { }

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Column Column { Text("Hello World") Text("Hello World") Text("Hello World") } Hello World Hello World Hello World

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Column Column( verticalArrangement = ) { Text("Hello World") Text("Hello World") Text("Hello World") } X Y

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Column Column( 
 verticalArrangement = Arrangement.Center 
 ) { Text("Hello World") Text("Hello World") Text("Hello World") } Hello World Hello World Hello World

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Column Column( 
 Arrangement.SpaceBetween 
 ) { Text("Hello World") Text("Hello World") Text("Hello World") } Hello World Hello World Hello World

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Column Column( horizontalAlignment = ) { Text("Hello World") Text("Hello World") Text("Hello World") } X Y

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Column Column( 
 horizontalAlignment = Alignment.End 
 ) { Text("Hello World") Text("Hello World") Text("Hello World") } Hello World Hello World Hello World

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Column Column( 
 Alignment.CenterHorizontally 
 ) { Text("Hello World") Text("Hello World") Text("Hello World") } Hello World Hello World Hello World

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Row

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Row Row { Text(“Hello") Text("World") Text(“!") } HelloWorld!

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Row Row( horizontalArrangement = ) { Text("Hello World") Text("Hello World") Text("Hello World") } X Y

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Row Row( Arrangement.SpaceBetween ) { Text(“Hello") Text("World") Text(“!") } Hello World !

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Row Row( verticalAlignment = ) { Text("Hello World") Text("Hello World") Text("Hello World") } X Y

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Row Row( Alignment.CenterVertically ) { Text("Hello World") Text("Hello World") Text("Hello World") } HelloWorld!

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Column & Row Row Column Vertical Arrangement Horizontal Alignment Horizontal Arrangement Vertical Alignment

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Column & Row

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Column & Row Row { Image(…) Column { Text(“…”) Text(“…”) } }

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Column & Row Row { Image(…) Column { Text(“…”) Text(“…”) } }

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Column & Row Row { Image(…) Column { Text(“…”) Text(“…”) } }

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Layout Modifiers

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Layout Modifiers Column( Modifier.background(Color.Green) ) { Text(text = “Hello World”) Text(text = "Hello World") } Hello World Hello World

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Layout Modifiers Column( 
 Modifier .background(Color.Green) .fillMaxWidth() ) { Text(text = “Hello World”) Text(text = "Hello World") } Hello World Hello World

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Layout Modifiers Column( 
 Modifier .background(Color.Green) .fillMaxSize() ) { Text(text = “Hello World”) Text(text = "Hello World") } Hello World Hello World

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Layout Modifiers Column( 
 Modifier .background(Color.Green) .width(200.dp) ) { Text(text = “Hello World”) Text(text = "Hello World") } Hello World Hello World 200dp

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Box

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Box Box { Image(…) }

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Box Box { Image(…) Column { 
 Text(…) Text(…) } }

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Box Box { Image(…) Column( Modifier.align( Alignment.BottomEnd ) ) { 
 Text(…) Text(…) } }

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List

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List @Composable fun EmployeeListView(items: List) { LazyColumn { items(names) { name -> Text(text = name) } } }

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List @Composable fun EmployeeListView(items: List) { LazyColumn { items(items) { item -> Text(text = name) } } }

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List @Composable fun EmployeeListView(items: List) { LazyColumn { items(items) { item -> ItemRow(item) } } }

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Slot Layouts

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Scaffold Scaffold( topBar = { } ) { }

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Scaffold Scaffold( topBar = { Text(text = "Home") } ) { } Home

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Scaffold Scaffold( topBar = { Text(text = "Home") } ) { Text(text = “Hello World”) } Home Hello World

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Layouts ● Column ● Row ● Box ● Scaffold

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Managing State

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Managing State ● Setup state using mutableStateOf

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Managing State 0 + -

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Managing State 0 var counter by remember { mutableStateOf(0) }

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Managing State 0 Column { Text( text = counter.toString() ) ... }

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Managing State 0 + - Button( onClick = { counter ++ } ) { Text(text = "+") }

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Managing State 0 + - Button( onClick = { counter -- } ) { Text(text = “-") }

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Recomposition Event Composable UI-Redraw

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Managing State 0 var counter by remember { mutableStateOf(0) } + -

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Managing State ● Setup state using mutableStateOf ● Setting up search

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Managing State Search

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Managing State Search Search View View Model Event

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Managing State Search @Composable fun SearchView() { }

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Managing State Search @Composable fun SearchView() { var query by remember { mutableStateOf("") } }

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Managing State Search @Composable fun SearchView() { OutlinedTextField( value = query ) }

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Managing State Search @Composable fun SearchView() { OutlinedTextField( onValueChange = { query = it } ) }

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Managing State Search @Composable fun SearchView() { OutlinedTextField( keyboardOptions = KeyboardOptions( imeAction = ImeAction.Search ) ) }

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Managing State Search @Composable fun SearchView() { OutlinedTextField( keyboardOptions = KeyboardActions( onSearch = { } ) ) }

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Managing State Search @Composable fun SearchView(onSearch: (String) -> Unit) { OutlinedTextField( keyboardOptions = KeyboardActions( onSearch = { } ) ) }

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Managing State Search @Composable fun SearchView(onSearch: (String) -> Unit) { OutlinedTextField( keyboardOptions = KeyboardActions( onSearch = { onSearch(query) } ) ) }

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Managing State Search Search View View Model Event

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Managing State Search SearchView { query -> viewModel.onSearch(query) }

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Managing State ● Setup state using mutableStateOf ● Setting up search ● Working with Flows

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Flows View View Model

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Flows ● collectAsState

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Flows class MyViewModel: ViewModel() { val stateFlow = _stateFlow.asStateFlow() }

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Flows @Composable fun HomeView() { viewModel.stateFlow.collectAsState() }

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Managing State ● flow.collectAsState ● liveData.observeAsState ● observable.subscribeAsState

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Managing State ● Setup state using mutableStatOf ● Setting up search ● Working with Flows

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Side Effects

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What is a side effect? ● Work outside of composable function ● Open new screen when tapping button ● Show no network message

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Side Effects ● Launched Effect ● Disposable Effect

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Launched Effect ● Triggers on first composition or key change

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Launched Effect @Composable fun HomeView() { 
 var counter by remember { mutableStateOf(0) } LaunchedEffect(key1 = Unit) { while (true) { delay(2000) counter ++ } } }

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Launched Effect @Composable fun HomeView() { 
 var counter by remember { mutableStateOf(0) } LaunchedEffect(key1 = Unit) { while (true) { delay(2000) counter ++ } } }

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Launched Effect @Composable fun HomeView() { 
 var counter by remember { mutableStateOf(0) } LaunchedEffect(key1 = Unit) { while (true) { delay(2000) counter ++ } } }

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Launched Effect @Composable fun HomeView() { 
 var counter by remember { mutableStateOf(0) } LaunchedEffect(key1 = Unit) { while (true) { delay(2000) counter ++ } } }

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Disposable Effect ● Triggers on first composition or key change ● Calls onDispose on terminate

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Disposable Effect @Composable fun HomeView() { DisposableEffect( ... ) { onDispose { callback.remove() } } }

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Side Effects ● Launched Effect ● Disposable Effect

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Introduction to Jetpack Compose ● Thinking in Compose ● Layouts ● Managing State ● Side Effects

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Thank You! www.codingwithmohit.com @heyitsmohit