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LifecycleSnippets.kt
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LifecycleSnippets.kt
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/*
* Copyright 2023 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.compose.snippets.lifecycle
import android.media.Image
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.Stable
import androidx.compose.runtime.State
import androidx.compose.runtime.key
import com.example.compose.snippets.sideeffects.Movie
import com.example.compose.snippets.sideeffects.Result
import com.example.compose.snippets.sideeffects.loadNetworkImage
// [START android_compose_lifecycle_1]
@Composable
fun MyComposable() {
Column {
Text("Hello")
Text("World")
}
}
// [END android_compose_lifecycle_1]
// [START android_compose_lifecycle_2]
@Composable
fun LoginScreen(showError: Boolean) {
if (showError) {
LoginError()
}
LoginInput() // This call site affects where LoginInput is placed in Composition
}
@Composable
fun LoginInput() { /* ... */ }
@Composable
fun LoginError() { /* ... */ }
// [END android_compose_lifecycle_2]
// [START android_compose_lifecycle_3]
@Composable
fun MoviesScreen(movies: List<Movie>) {
Column {
for (movie in movies) {
// MovieOverview composables are placed in Composition given its
// index position in the for loop
MovieOverview(movie)
}
}
}
// [END android_compose_lifecycle_3]
// [START android_compose_lifecycle_4]
@Composable
fun MovieOverview(movie: Movie) {
Column {
// Side effect explained later in the docs. If MovieOverview
// recomposes, while fetching the image is in progress,
// it is cancelled and restarted.
val image = loadNetworkImage(movie.url)
MovieHeader(image)
/* ... */
}
}
// [START_EXCLUDE silent]
@Composable
fun MovieHeader(image: State<Result<Image>>) { }
// [END_EXCLUDE]
// [END android_compose_lifecycle_4]
// [START android_compose_lifecycle_5]
@Composable
fun MoviesScreenWithKey(movies: List<Movie>) {
Column {
for (movie in movies) {
key(movie.id) { // Unique ID for this movie
MovieOverview(movie)
}
}
}
}
// [END android_compose_lifecycle_5]
// [START android_compose_lifecycle_6]
@Composable
fun MoviesScreenLazy(movies: List<Movie>) {
LazyColumn {
items(movies, key = { movie -> movie.id }) { movie ->
MovieOverview(movie)
}
}
}
// [END android_compose_lifecycle_6]
// [START android_compose_lifecycle_7]
// Marking the type as stable to favor skipping and smart recompositions.
@Stable
interface UiState<T : Result<T>> {
val value: T?
val exception: Throwable?
val hasError: Boolean
get() = exception != null
}
// [END android_compose_lifecycle_7]