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Tip5.kt
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Tip5.kt
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package com.cupsofcode.recomposition_examples
import androidx.compose.animation.AnimatedVisibility
import androidx.compose.animation.slideInVertically
import androidx.compose.animation.slideOutVertically
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.material.*
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.outlined.AccountCircle
import androidx.compose.material.icons.outlined.Favorite
import androidx.compose.material.icons.outlined.Home
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import com.cupsofcode.recomposition_examples.ui.theme.*
import kotlinx.coroutines.delay
/**
* tip 5: utilize `derivedStateOf()` to buffer the rate of changes thus limiting the
* number of recompositions.
*
* If any object depends on a certain state object, that is frequently changed, all composable
* functions listening to that object, will recompose more than they need to.
*
* Wrap that object in `derivedStateOf()` to limit the number of recompositions.
*
*/
@Composable
fun Tip5() {
val initialList = arrayListOf<FruitRow>(
FruitRow("Apple", Gray200),
FruitRow("Orange", Brown200),
FruitRow("Strawberry", Green700),
FruitRow("Blueberry", Brown500),
FruitRow("Banana", Green200),
FruitRow("Watermelon", Gray200),
FruitRow("Cantaloupe", Brown200),
FruitRow("Mango", Green700),
FruitRow("Apricot", Brown500),
FruitRow("Lemon", Green200),
FruitRow("Grapes", Gray200),
FruitRow("Peach", Brown200),
FruitRow("Pear", Green700),
FruitRow("Kiwi", Brown500),
FruitRow("Honeydew", Green200),
FruitRow("Pineapple", Gray200),
FruitRow("Coconut", Brown200),
FruitRow("Plum", Green700),
)
Column(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("column"),
horizontalAlignment = Alignment.CenterHorizontally,
verticalArrangement = Arrangement.Center
) {
GoodGreetingsTip5(initialList)
// BadGreetingsTip5 (initialList)
}
}
/**
* 👍 : Only BottomBar gets recomposed whenever hideBottomBar's calculated state changes,
* but top-level Scaffold and LazyColumns don't.
*/
@Composable
private fun GoodGreetingsTip5(list: List<FruitRow>) {
val listState = rememberLazyListState()
LaunchedEffect(key1 = list, block = {
delay(500)
listState.animateScrollToItem(list.lastIndex)
delay(500)
listState.animateScrollToItem(0)
})
val hideBottomBar = remember {
derivedStateOf { listState.isScrollInProgress }
}
Scaffold(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("scaffold"),
bottomBar = {
AnimatedVisibility(
visible = !hideBottomBar.value,
enter = slideInVertically(
initialOffsetY = { fullHeight -> fullHeight }
),
exit = slideOutVertically(
targetOffsetY = { fullHeight -> fullHeight }
)
) {
BottomAppBar(
modifier = Modifier
.fillMaxWidth()
.background(color = Background200)
.recomposeHighlighter()
.recompositionCounter("bottombar"),
elevation = 32.dp,
content = {
BottomNavigationItems()
}
)
}
},
content = {
LazyColumn(
state = listState,
modifier = Modifier
.fillMaxWidth()
.recomposeHighlighter()
.recompositionCounter("lazy column")
) {
items(
items = list,
key = { it.name }
) { fruit ->
Item(fruit)
}
}
}
)
}
/**
* 👎 : everything including top-level Scaffold gets recomposed, because hideBottomBar
* depends on the calculated result of the frequent changing isScrollInProgress
* variable in listState.
*/
@Composable
private fun BadGreetingsTip5(list: List<FruitRow>) {
val listState = rememberLazyListState()
LaunchedEffect(key1 = list, block = {
delay(500)
listState.animateScrollToItem(list.lastIndex)
delay(500)
listState.animateScrollToItem(0)
})
val hideBottomBar = listState.isScrollInProgress
Scaffold(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("scaffold"),
bottomBar = {
AnimatedVisibility(
visible = !hideBottomBar,
enter = slideInVertically(
initialOffsetY = { fullHeight -> fullHeight }
),
exit = slideOutVertically(
targetOffsetY = { fullHeight -> fullHeight }
)
) {
BottomAppBar(
modifier = Modifier
.fillMaxWidth()
.background(color = Background200)
.recomposeHighlighter()
.recompositionCounter("bottombar"),
elevation = 32.dp,
content = {
BottomNavigationItems()
}
)
}
},
content = {
LazyColumn(
state = listState,
modifier = Modifier
.fillMaxWidth()
.recomposeHighlighter()
.recompositionCounter("lazy column")
) {
items(
items = list,
key = { it.name }
) { fruit ->
Item(fruit)
}
}
}
)
}
@Composable
private fun BottomNavigationItems() {
BottomNavigation {
BottomNavigationItem(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("bottomNav item 1")
.background(color = Background200),
selected = true, onClick = { }, icon = {
Icon(Icons.Outlined.Home, "")
},
label = {
Text(text = "Home")
}
)
BottomNavigationItem(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("bottomNav item 1")
.background(color = Background200),
selected = false, onClick = { }, icon = {
Icon(Icons.Outlined.AccountCircle, "")
},
label = {
Text(text = "Circle")
}
)
BottomNavigationItem(
modifier = Modifier
.recomposeHighlighter()
.recompositionCounter("bottomNav item 1")
.background(color = Background200),
selected = false, onClick = { }, icon = {
Icon(Icons.Outlined.Favorite, "")
},
label = {
Text(text = "Favorite")
}
)
}
}