360|AnDev 2020: Learning Jetpack Compose By Example

Over the course of the last few years Android development has gone through significant changes in how we structure our apps, the language we use for development, the tooling & libraries that help us speed up our development and the improvements in testing our apps. What had not changed in all these years is the Android UI toolkit. This changes with Jetpack Compose that aims to reimagine what Android UI development would look like using declarative programming principles. It is heavily influenced by existing web and mobile frameworks such as React, Litho, Vue & Flutter and would be a paradigm shift in Android UI development as we know it.

In this talk, we will take a deeper look at what declarative programming means and how we should think about it when building our apps. We will look into the main principles of Jetpack Compose and try to draw parallels with the “old Android way” of doing common tasks. Lastly, we will dive into various code examples and learn how to build layouts, manage state, write custom views, style our views, access resources and more, all using Jetpack Compose.

Companion code – https://github.com/vinaygaba/Learn-Jetpack-Compose-By-Example

Transcript

2. Why do we need Jetpack Compose?
3. Why do I need to learn new things? UI Toolkit is tied to the OS State Management is tricky Lots of context switching Simple things still require a lot of code
4. Why do I need to learn new things? UI Toolkit is tied to the OS State Management is tricky Lots of context switching Simple things still require a lot of code
5. Why do I need to learn new things? UI Toolkit is tied to the OS State Management is tricky Lots of context switching Simple things still require a lot of code
6. Why do I need to learn new things? UI Toolkit is tied to the OS State Management is tricky Lots of context switching Simple things still require a lot of code
7. Why do I need to learn new things? UI Toolkit is tied to the OS State Management is tricky Lots of context switching Simple things still require a lot of code
8. Examples
9. Disclaimer Examples are based on 0.1.0-dev14 version Compose is still pre-alpha so things are constantly changing and will continue to do so Alpha release is expected in the next few months
10. Disclaimer Examples are based on 0.1.0-dev14 version Compose is still pre-alpha so things are constantly changing and will continue to do so Alpha release is expected in the next few months
11. Disclaimer Examples are based on 0.1.0-dev14 version Compose is still pre-alpha so things are constantly changing and will continue to do so Alpha release is expected in the next few months
12. Disclaimer Examples are based on 0.1.0-dev14 version Compose is still pre-alpha so things are constantly changing and will continue to do so Alpha release is expected in the next few months
13. Example: Hello World
14. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) } }
15. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { } } }
16. fun ComponentActivity.setContent( recomposer: Recomposer = Recomposer.current(), content: @Composable () -> Unit ): Composition { // Some magic ✨ }
17. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { } } }
18. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { Text(text = "Hello World") } } }
19. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { Text(text = "Hello World") } } }
20. class HelloWorldActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { Text(text = "Hello World") } } }
21. @Composable fun CustomTextComponent() { Text(text = "Hello World") }
22. @Composable fun CustomTextComponent(displayText: String) { Text( text = displayText, style = TextStyle( fontSize = 18.sp, fontFamily = FontFamily.Monospace ) ) }
23. @Composable fun CustomTextComponent(displayText: String) { Text( text = displayText, style = TextStyle( fontSize = 18.sp, fontFamily = FontFamily.Monospace ) ) }
24. @Composable fun CustomTextComponent(displayText: String) { Text( text = displayText, style = TextStyle( fontSize = 18.sp, fontFamily = FontFamily.Monospace ) ) } @Preview @Composable fun CustomTextComponentPreview() { CustomTextComponent("Hello World") }
27. Example: Show an Image
28. @Composable fun DrawableImage() { }
29. @Composable fun DrawableImage() { val image = loadImageResource(R.drawable.lena) }
30. @Composable fun DrawableImage() { val image = loadImageResource(R.drawable.lena) image.resource.resource?.let { Image(asset = it, modifier = Modifier.preferredSize(200.dp)) } }
31. @Composable fun DrawableImage(@DrawableRes resId: Int) { val image = loadImageResource(resId) image.resource.resource?.let { Image(asset = it, modifier = Modifier.preferredSize(200.dp)) } }
32. @Composable fun DrawableImage(@DrawableRes resId: Int) { val image = loadImageResource(resId) image.resource.resource?.let { Image(asset = it, modifier = Modifier.preferredSize(200.dp)) } }
33. Example: Alert Dialog
34. // Classic Android AlertDialog.Builder(context) .setTitle("360|AnDev") .setMessage("Isn't this conference amazing?") .setPositiveButton(android.R.string.yes, null) .setNegativeButton(android.R.string.no, null) .setIcon(android.R.drawable.ic_dialog_alert) .show()
35. @Composable fun AlertDialogComponent() { }
36. @Composable fun AlertDialogComponent() { var showPopup by state { false } }
37. @Composable fun AlertDialogComponent() { var showPopup by state { false } Button(onClick = { showPopup = true }, backgroundColor = Color.DarkGray) { Text(text = "Click Me") } }
38. @Composable fun AlertDialogComponent() { var showPopup by state { false } Button(onClick = { showPopup = true }, backgroundColor = Color.DarkGray) { Text(text = "Click Me") } if (showPopup) { AlertDialog( onCloseRequest = { showPopup = false }, text = { Text("Congratulations! You just clicked the text successfully") }, confirmButton = { Button( onClick = onPopupDismissed ) { Text(text = "Ok") } } ) } }
39. @Composable fun AlertDialogComponent() { var showPopup by state { false } Button(onClick = { showPopup = true }, backgroundColor = Color.DarkGray) { Text(text = "Click Me") } if (showPopup) { AlertDialog( onCloseRequest = { showPopup = false }, text = { Text("Congratulations! You just clicked the text successfully") }, confirmButton = { Button( onClick = onPopupDismissed ) { Text(text = "Ok") } } ) } }
40. @Composable fun AlertDialogComponent() { var showPopup by remember { mutableStateOf(false) } val onButtonClicked = { showPopup = true } val onPopupDismissed = { showPopup = false } if (!showPopup) { Button(onClick = onButtonClicked, backgroundColor = Color.DarkGray) { Text(text = "Click Me") } } else { AlertDialog( onCloseRequest = onPopupDismissed, text = { Text("Congratulations! You just clicked the text successfully") }, confirmButton = { Button( onClick = onPopupDismissed ) { Text(text = "Ok") } } ) } }
41. Example: Simple Layouts
43. Row
44. Row 1 2
45. 1 Column 1 Row 2
46. @Composable fun ImageWithTitleSubtitleComponent() { }
47. @Composable fun ImageWithTitleSubtitleComponent() { Row() { Column() { } } }
48. @Composable fun ImageWithTitleSubtitleComponent() { Row(modifier = Modifier.fillMaxWidth() + Modifier.padding(16.dp)) { Column(modifier = Modifier.padding(start = 16.dp)) { } } }
49. @Composable fun ImageWithTitleSubtitleComponent() { Row(modifier = Modifier.fillMaxWidth() + Modifier.padding(16.dp)) { DrawableImage(R.drawable.lenna) Column(modifier = Modifier.padding(start = 16.dp)) { CustomTextComponent(displayText = "Title") CustomTextComponent(displayText = "Subtitle") } } }
50. @Composable fun ImageWithTitleSubtitleComponent(title: String, subtitle: String, imageUrl: String) { Row(modifier = Modifier.fillMaxWidth() + Modifier.padding(16.dp)) { NetworkImage(imageUrl) Column(modifier = Modifier.padding(start = 16.dp)) { CustomTextComponent(displayText = title) CustomTextComponent(displayText = subtitle) } } }
51. @Composable fun ImageWithTitleSubtitleComponent(title: String, subtitle: String, imageUrl: String) { Row(modifier = Modifier.fillMaxWidth() + Modifier.padding(16.dp)) { NetworkImage(imageUrl) Column(modifier = Modifier.padding(start = 16.dp)) { CustomTextComponent(displayText = title) CustomTextComponent(displayText = subtitle) } } }
52. Example: ConstraintLayout
53. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { }
54. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { ConstraintLayout { val (title, subtitle, image) = createRefs() } }
55. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { ConstraintLayout { val (title, subtitle, image) = createRefs() CustomTextComponent( displayText = titleText, ) CustomTextComponent( displayText = subtitleText, ) NetworkImage( url = imageUrl, ) } }
56. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { ConstraintLayout { val (title, subtitle, image) = createRefs() CustomTextComponent( displayText = titleText, modifier = Modifier.constrainAs(title) { start.linkTo(image.end, margin = 8.dp) top.linkTo(image.top) } ) CustomTextComponent( displayText = subtitleText, ) NetworkImage( url = imageUrl, ) } }
57. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { ConstraintLayout { val (title, subtitle, image) = createRefs() CustomTextComponent( displayText = titleText, modifier = Modifier.constrainAs(title) { start.linkTo(image.end, margin = 8.dp) top.linkTo(image.top) } ) CustomTextComponent( displayText = subtitleText, modifier = Modifier.constrainAs(subtitle) { bottom.linkTo(image.bottom) start.linkTo(image.end, margin = 8.dp) } ) NetworkImage( url = imageUrl, modifier = Modifier.constrainAs(image) { centerVerticallyTo(parent) start.linkTo(parent.start, margin = 16.dp) top.linkTo(parent.top, margin = 16.dp) bottom.linkTo(parent.bottom, margin = 16.dp) } ) } }
58. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp), shape = RoundedCornerShape(4.dp) ) { ConstraintLayout { val (title, subtitle, image) = createRefs() CustomTextComponent( displayText = titleText, modifier = Modifier.constrainAs(title) { start.linkTo(image.end, margin = 8.dp) top.linkTo(image.top) } ) CustomTextComponent( displayText = subtitleText, modifier = Modifier.constrainAs(subtitle) { bottom.linkTo(image.bottom) start.linkTo(image.end, margin = 8.dp) } ) NetworkImage( url = imageUrl, modifier = Modifier.constrainAs(image) { centerVerticallyTo(parent) start.linkTo(parent.start, margin = 16.dp) top.linkTo(parent.top, margin = 16.dp) bottom.linkTo(parent.bottom, margin = 16.dp) }) } } }
59. @Composable fun SimpleRowComponent(titleText: String, subtitleText: String, imageUrl: String) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp), shape = RoundedCornerShape(4.dp) ) { ConstraintLayout { val (title, subtitle, image) = createRefs() CustomTextComponent( displayText = titleText, modifier = Modifier.constrainAs(title) { start.linkTo(image.end, margin = 8.dp) top.linkTo(image.top) } ) CustomTextComponent( displayText = subtitleText, modifier = Modifier.constrainAs(subtitle) { bottom.linkTo(image.bottom) start.linkTo(image.end, margin = 8.dp) } ) NetworkImage( url = imageUrl, modifier = Modifier.constrainAs(image) { centerVerticallyTo(parent) start.linkTo(parent.start, margin = 16.dp) top.linkTo(parent.top, margin = 16.dp) bottom.linkTo(parent.bottom, margin = 16.dp) }) } } }
61. Example: List
64. www.JetpackCompose.app
65. @Composable fun ListComponent(superheroList: List<Person>) { }
66. @Composable fun ListComponent(superheroList: List<Person>) { LazyColumnItems(items = superheroList) { person -> } }
67. @Composable fun ListComponent(superheroList: List<Person>) { LazyColumnItems(items = superheroList) { person -> SimpleRowComponent( person.name, person.age, person.profilePictureUrl ) } }
68. @Composable fun ListComponent(superheroList: List<Person>) { LazyColumnItems(items = superheroList) { person -> SimpleRowComponent( person.name, person.age, person.profilePictureUrl ) } }
69. Example: Click
70. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp), shape = RoundedCornerShape(4.dp) ) { .... .... } }
71. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, viewModel: SuperheroViewModel ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.cl shape = RoundedCornerShape(4.dp) ) { .... .... } }
72. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, viewModel: SuperheroViewModel ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.cl shape = RoundedCornerShape(4.dp) ) { .... .... } } clip clickable clipToBounds
73. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, viewModel: SuperheroViewModel ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.clickable { viewModel.updateSelectedSuperhero() }, shape = RoundedCornerShape(4.dp) ) { .... .... } }
74. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, viewModel: SuperheroViewModel ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.clickable { viewModel.updateSelectedSuperhero() }, shape = RoundedCornerShape(4.dp) ) { .... .... } }
75. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, onClick: () -> Unit ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.clickable { onClick() }, shape = RoundedCornerShape(4.dp) ) { .... .... } }
76. @Composable fun SimpleRowComponent( titleText: String, subtitleText: String, imageUrl: String, onClick: () -> Unit ) { Card( modifier = Modifier.fillMaxWidth() + Modifier.padding(8.dp) + Modifier.clickable { onClick() }, shape = RoundedCornerShape(4.dp) ) { .... .... } }
77. Example: Pinch-to-Zoom & Drag
78. @Composable fun ZoomableImageComponent(imageUrl: String) { }
79. @Composable fun ZoomableImageComponent(imageUrl: String) { var scale by state { 1f } var panOffset by state { Offset(0f, 0f) } }
80. @Composable fun ZoomableImageComponent(imageUrl: String) { var scale by state { 1f } var panOffset by state { Offset(0f, 0f) } Box(gravity = Alignment.Center) { NetworkImage( imageUrl = imageUrl, modifier = Modifier.fillMaxSize() ) } }
81. @Composable fun ZoomableImageComponent(imageUrl: String) { var scale by state { 1f } var panOffset by state { Offset(0f, 0f) } Box( gravity = Alignment.Center, modifier = Modifier.zoomable(onZoomDelta = { scale *= it }) ) { NetworkImage( imageUrl = imageUrl, modifier = Modifier.fillMaxSize() + Modifier.drawLayer( scaleX = scale, scaleY = scale ) ) } }
82. @Composable fun ZoomableImageComponent(imageUrl: String) { var scale by state { 1f } var panOffset by state { Offset(0f, 0f) } Box( gravity = Alignment.Center, modifier = Modifier.zoomable(onZoomDelta = { scale *= it }) + Modifier.rawDragGestureFilter( object : DragObserver { override fun onDrag(dragDistance: Offset): Offset { panOffset = panOffset.plus(dragDistance) return super.onDrag(dragDistance) } }) ) { NetworkImage( imageUrl = imageUrl, modifier = Modifier.fillMaxSize() + Modifier.drawLayer( scaleX = scale, scaleY = scale, translationX = panOffset.x, translationY = panOffset.y ) ) } }
83. @Composable fun ZoomableImageComponent(imageUrl: String) { var scale by state { 1f } var panOffset by state { Offset(0f, 0f) } Box( gravity = Alignment.Center, modifier = Modifier.zoomable(onZoomDelta = { scale *= it }) + Modifier.rawDragGestureFilter( object : DragObserver { override fun onDrag(dragDistance: Offset): Offset { panOffset = panOffset.plus(dragDistance) return super.onDrag(dragDistance) } }) ) { NetworkImage( imageUrl = imageUrl, modifier = Modifier.fillMaxSize() + Modifier.drawLayer( scaleX = scale, scaleY = scale, translationX = panOffset.x, translationY = panOffset.y ) ) } }
84. Interoperability
85. Example: Compose in Classic Android
86. class ComposeInClassicAndroidActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_compose_in_classic_android) } }
87. class ComposeInClassicAndroidActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_compose_in_classic_android) val containerLayout = findViewById(R.id.frame_container) containerLayout.setContent(Recomposer.current()) { SimpleRowComponent() } } }
88. class ComposeInClassicAndroidActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_compose_in_classic_android) val containerLayout = findViewById(R.id.frame_container) containerLayout.setContent(Recomposer.current()) { SimpleRowComponent() } } }
89. Example: Classic Android in Compose
90. <?xml version="1.0" encoding="utf-8"?> <com.vinaygaba.creditcardview.CreditCardView xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:id=“@+id/credit_card" android:layout_width="fill_parent" android:layout_height="225dp" app:cardName="John Doe" app:cardNumber="5500005555555559" app:cardNumberFormat="masked_all_but_last_four" app:expiryDate="02/22" app:putChip="true" app:type=“auto" /> credit_card.xml
91. @Composable fun AndroidInCompose() { AndroidView(R.layout.credit_card, modifier = Modifier.padding(16.dp)) }
92. Resources
93. https://bit.ly/ComposeByExample
94. https://www.JetpackCompose.app/