Develop Reference

TabRow/Tab Recomposition Issue in Compose Accompanist Pager

I was trying to create a sample Tab View in Jetpack compose, so the structure will be like
Inside a Parent TabRow we are iterating the tab title and create Tab composable.
More precise code will be like this.
#OptIn(ExperimentalPagerApi::class)
#Composable
private fun MainApp() {
Scaffold(
topBar = {
TopAppBar(
title = { Text(stringResource(R.string.app_name)) },
backgroundColor = MaterialTheme.colors.surface
)
},
modifier = Modifier.fillMaxSize()
) { padding ->
Column(Modifier.fillMaxSize().padding(padding)) {
val pagerState = rememberPagerState()
val coroutineScope = rememberCoroutineScope()
val tabContents = listOf(
"Home" to Icons.Filled.Home,
"Search" to Icons.Filled.Search,
"Settings" to Icons.Filled.Settings
)
HorizontalPager(
count = tabContents.size,
state = pagerState,
contentPadding = PaddingValues(horizontal = 32.dp),
modifier = Modifier
.weight(1f)
.fillMaxWidth()
) { page ->
PagerSampleItem(
page = page
)
}
TabRow(
selectedTabIndex = pagerState.currentPage,
backgroundColor = MaterialTheme.colors.surface,
contentColor = MaterialTheme.colors.onSurface,
indicator = { tabPositions ->
TabRowDefaults.Indicator(
Modifier
.pagerTabIndicatorOffset(pagerState, tabPositions)
.height(4.dp)
.background(
color = Color.Green,
shape = RectangleShape
)
)
}
) {
tabContents.forEachIndexed { index, pair: Pair<String, ImageVector> ->
Tab(
selected = pagerState.currentPage == index,
selectedContentColor = Color.Green,
unselectedContentColor = Color.Gray,
onClick = {
coroutineScope.launch {
pagerState.animateScrollToPage(index)
}
},
text = { Text(text = pair.first) },
icon = { Icon(imageVector = pair.second, contentDescription = null) }
)
}
}
}
}
}
#Composable
internal fun PagerSampleItem(
page: Int
) {
// Displays the page index
Text(
text = page.toString(),
modifier = Modifier
.padding(16.dp)
.background(MaterialTheme.colors.surface, RoundedCornerShape(4.dp))
.sizeIn(minWidth = 40.dp, minHeight = 40.dp)
.padding(8.dp)
.wrapContentSize(Alignment.Center)
)
}
And coming to my question is whenever we click on the tab item, the inner content get recompose so weirdly. Im not able to understand why it is happens.
Am attaching an image of the recomposition counts below, please take a look that too, it would be good if you guys can help me more for understand this, also for future developers.
There are two question we have to resolve in this stage
Whether it will create any performance issue, when the view getting more complex
How to resolve this recompostion issue
Thanks alot.

… whenever we click on the tab item, the
inner content get recompose so weirdly. Im not able to understand why
it is happens...
It's hard to determine what this "weirdness" is, there could be something inside the composable your'e mentioning here.
You also didn't specify what the API is, so I copied and pasted your code and integrated accompanist view pager, then I was able to run it though not on an Android Studio with a re-composition count feature.
And since your'e only concerned about the Text and the Icon parameter of the API, I think that's something out of your control. I suspect the reason why your'e getting those number of re-composition count is because your'e animating the page switching.
coroutineScope.launch {
pagerState.animateScrollToPage(index)
}
Though 'm not able to try this on another Android Studio version with the re-composition feature, I think (though I'm not sure) scrolling to another page without animation will yield less re-composition count.
coroutineScope.launch {
pagerState.scrollToPage(index)
}
If it still bothers you, the best course of action is to ask them directly, though personally I wouldn't concerned much about this as they are part of an accepted API and its just Text and Icon being re-composed many times by an animation which is also fine IMO.
Now if you have some concerns about your PagerSampleItem stability(which you have a full control), based on the provided code and screenshot, I think your'e fine.
There's actually a feature suggested from this article to check the stability of a composable, I run it and I got this report.
restartable skippable scheme("[androidx.compose.ui.UiComposable]") fun PagerSampleItem(
stable page: Int
)
Everything about this report is within the article I linked.
Also, your Text and Icon are using String and ImageVector which is stable and immutable (marked by #Immutable) respectively.
So TLDR, IMO your code is fine, your PagerSampleItem is not re-composing in the screenshot.

Composable invocations can only happen from the context of a #Composable function

I have a composable function that i need to call after clicking a button but it keeps showing an error that composables cannot be executed from button clicks , can anyone please guide me to solve this issue Thank you
This is my code
Box(contentAlignment = Alignment.Center) {
Button(onClick = {
// This is a composable function that i need to call
SignUpNewUser(email,fullName,country,password)
}
,modifier = Modifier
.width(200.dp)
.background(color = Color.DarkGray)) {
Text(text = "Sign Up",style = TextStyle(color = Color.White,fontWeight = FontWeight.Bold))
}
}

You can only add a #Composable view to another #Composable view.
onClick is not marked #Composable, so you get this warning. You can only change the state with onClick.
For example, you can create a flag and display the UI depending on that flag:
var signUp by remember { mutableStateOf(false) }
if (signUp) {
SignUpNewUser(email, fullName, country, password)
} else {
Box(contentAlignment = Alignment.Center) {
Button(onClick = {
signUp = true
}, modifier = Modifier
.width(200.dp)
.background(color = Color.DarkGray)) {
Text(text = "Sign Up", style = TextStyle(color = Color.White, fontWeight = FontWeight.Bold))
}
}
}
I suggest you start with this youtube video which explains the basic principles of when you need to use state in compose. You can continue deepening your knowledge with state in Compose documentation.
Another option would be to use Compose Navigation.

How can i add a Toolbar in Jetpack Compose?

I need to add a Toolbar in my Android application with a List like below. I am using Jetpack Compose to create the UI. Below is the composable function i am using for drawing the main view.
#Composable
fun HomeScreenApp() {
showPetsList(dogs = dogData)
}

You can use the TopAppBar.
The best way is to use the Scaffold. Something like:
Scaffold(
topBar = {
TopAppBar(
title = {
Text(text = "TopAppBar")
},
navigationIcon = {
IconButton(onClick = { }) {
Icon(Icons.Filled.Menu,"")
}
},
backgroundColor = ....,
contentColor = ....
)
}, content = {
})

In Jetpack compose Toolbar can be easily implemented by using a Composable function called TopAppBar. You need to place TopAppBar along with your main composable function inside a column.
#Composable
fun HomeScreenApp() {
Column() {
TopAppBar(title = { Text(text = "Adopt Me") }, backgroundColor = Color.Red)
showPetsList(dogs = dogData)
}
}
The above function calls the TopAppBar inside a column followed by your main content view. The TopAppBar function takes in a Text object(Not string) as title. This can also be any Composable function. You can also specify other params like backgroundColor, navigationIcon, contentColor etc. Remember that TopAppBar is just a Composable provided by Jetpack team. It can be your custom function also just in case you need more customization.
Output

Using Custom Views with Jetpack Compose

Let's suppose I'm using some library that's intended to provide some UI Widgets.
Let's say this library provides a Button Widget called FancyButton.
In the other hand, I have a new project created with Android Studio 4 that allows me to create a new project with an Empty Compose Activity.
The question is:
How should I add this FancyButton to the view stack? Is it possible? Or with Jetpack Compose I can only use components that had been developed specifically for Jetpack Compose. In this case, AFAIK I could only use Android standars components (Text, MaterialTheme, etc).
If I try to use something like this:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MaterialTheme {
Greeting("Android")
FancyButton(context, "Some text")
}
}
}
then I get this error:
e: Supertypes of the following classes cannot be resolved. Please make sure you have the required dependencies in the classpath.

Currently (as of 0.1.0-dev04), there is not a good solution to this. In the future, you'll be able to simply call it as FancyButton("Some text") (no context needed).
You can see a demo of what it will look like in the Compose code here.

Update in alpha 06
It is possible to import Android View instances in a composable.
Use ContextAmbient.current as the context parameter for the View.
Column(modifier = Modifier.padding(16.dp)) {
// CustomView using Object
MyCustomView(context = ContextAmbient.current)
// If the state updates
AndroidView(viewBlock = ::CustomView, modifier = modifier) { customView ->
// Modify the custom view
}
// Using xml resource
AndroidView(resId = R.layout.view_demo)
}

You can wrap your custom view within the AndroidView composable:
#Composable
fun RegularTextView() {
AndroidView(
factory = { context ->
TextView(context).apply {
text = "RegularTextView"
textSize = 34.dp.value
}
},
)
}
And here is how to update your custom view during a recomposition, by using the update parameter:
#Composable
fun RegularTextView() {
var string by remember {
mutableStateOf("RegularTextView")
}
Column(horizontalAlignment = Alignment.CenterHorizontally) {
AndroidView(
factory = { context ->
TextView(context).apply {
textSize = 34.dp.value
}
},
update = { textView ->
textView.text = string
}
)
Spacer(modifier = Modifier.height(8.dp))
Button(
onClick = {
string = "Button clicked"
},
) {
Text(text = "Update text")
}
}
}

#Composable
fun ButtonType1(text: String, onClick: () -> Unit)
{
Button (
modifier=Modifier.fillMaxWidth().height(50.dp),
onClick = onClick,
shape = RoundedCornerShape(5.dp),
border = BorderStroke(3.dp, colorResource(id = R.color.colorPrimaryDark)),
colors = ButtonDefaults.buttonColors(contentColor = Color.White, backgroundColor = colorResource(id = R.color.colorPrimaryDark))
)
{
Text(text = text , color = colorResource(id = R.color.white),
fontFamily = montserrat,
fontWeight = FontWeight.Normal,
fontSize = 15.sp
)
}
}

Does Android Jetpack Compose support Toolbar widget?

I'd like to use Toolbar with Jetpack Compose. Does it have such a Composable component?

You can use the TopAppBar.
The best way is to use it with the Scaffold. Something like:
Scaffold(
topBar = {
TopAppBar(
title = {
Text(text = "TopAppBar")
},
navigationIcon = {
IconButton(onClick = { }) {
Icon(Icons.Filled.Menu,"")
}
},
backgroundColor = Color.Blue,
contentColor = Color.White,
elevation = 12.dp
)
}, content = {
})

Using
compose_version = '1.0.0-beta01'
TopAppBar(
title = {
Text(text = "Pets Show")
},
navigationIcon = {
IconButton(onClick = { }) {
Icon(imageVector = Icons.Filled.Menu, contentDescription = "Menu Btn")
}
},
backgroundColor = Color.Transparent,
contentColor = Color.Gray,
elevation = 2.dp
)

TopAppBar is a pre-defined composable that will help you accomplish what you want. You can use it with Scaffold in order to get basic material design scaffolding to hook up the TopAppBar.
Here is an example with detailed comments to see how to use it - https://github.com/vinaygaba/Learn-Jetpack-Compose-By-Example/blob/1f843cb2bf18b9988a0dfc611b631f216f02149e/app/src/main/java/com/example/jetpackcompose/material/FixedActionButtonActivity.kt#L70
Copying it here to make it easy to consume
// Scaffold is a pre-defined composable that implements the basic material design visual
// layout structure. It takes in child composables for all the common elements that you see
// in an app using material design - app bar, bottom app bar, floating action button, etc. It
// also takes care of laying out these child composables in the correct positions - eg bottom
// app bar is automatically placed at the bottom of the screen even though I didn't specify
// that explicitly.
Scaffold(
scaffoldState = scaffoldState,
topAppBar = { TopAppBar(title = { Text("Scaffold Examples") }) },
bottomAppBar = { fabConfiguration ->
// We specify the shape of the FAB bu passing a shape composable (fabShape) as a
// parameter to cutoutShape property of the BottomAppBar. It automatically creates a
// cutout in the BottomAppBar based on the shape of the Floating Action Button.
BottomAppBar(fabConfiguration = fabConfiguration, cutoutShape = fabShape) {}
},
floatingActionButton = {
FloatingActionButton(
onClick = {},
// We specify the same shape that we passed as the cutoutShape above.
shape = fabShape,
// We use the secondary color from the current theme. It uses the defaults when
// you don't specify a theme (this example doesn't specify a theme either hence
// it will just use defaults. Look at DarkModeActivity if you want to see an
// example of using themes.
backgroundColor = MaterialTheme.colors.secondary
) {
IconButton(onClick = {}) {
Icon(asset = Icons.Filled.Favorite)
}
}
},
floatingActionButtonPosition = Scaffold.FabPosition.CenterDocked,
bodyContent = { modifier ->
// Vertical scroller is a composable that adds the ability to scroll through the
// child views
VerticalScroller {
// Column is a composable that places its children in a vertical sequence. You
// can think of it similar to a LinearLayout with the vertical orientation.
Column(modifier) {
repeat(100) {
// Card composable is a predefined composable that is meant to represent
// the card surface as specified by the Material Design specification. We
// also configure it to have rounded corners and apply a modifier.
Card(color = colors[it % colors.size],
shape = RoundedCornerShape(8.dp),
modifier = Modifier.padding(8.dp)
) {
Spacer(modifier = Modifier.fillMaxWidth() + Modifier.preferredHeight(200.dp))
}
}
}
}
}
)

Yes, it's TopAppBar (in androidx.ui.material). It allows you to specify a title, color, navigation icon, and actions. See the documentation for more information.