我正在学习 Kotlin 移动应用程序开发，并关注 https://developer.android.com/codelabs/basic-android-kotlin-compose-woof-animation? 的 Google Codelab。这是我显示狗列表的代码：
/*
* Copyright (C) 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.woof
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.annotation.DrawableRes
import androidx.annotation.StringRes
import androidx.compose.foundation.Image
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.size
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.layout.Spacer
import androidx.compose.material3.Card
import androidx.compose.material3.CenterAlignedTopAppBar
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Surface
import androidx.compose.material.icons.filled.ExpandMore
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.ExpandLess
import androidx.compose.material3.Icon
import androidx.compose.material3.IconButton
import androidx.compose.material3.Text
import androidx.compose.animation.animateContentSize
import androidx.compose.animation.animateColorAsState
import androidx.compose.animation.core.Spring
import androidx.compose.animation.core.spring
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.layout.ContentScale
import androidx.compose.ui.res.dimensionResource
import androidx.compose.ui.res.painterResource
import androidx.compose.ui.res.stringResource
import androidx.compose.ui.tooling.preview.Preview
import com.example.woof.data.Dog
import com.example.woof.data.dogs
import com.example.woof.ui.theme.WoofTheme
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
WoofTheme {
// A surface container using the 'background' color from the theme
Surface(
modifier = Modifier.fillMaxSize()
) {
WoofApp()
}
}
}
}
}
/**
* Composable that displays an app bar and a list of dogs.
*/
@Composable
fun WoofApp() {
Scaffold(
topBar = {
WoofTopAppBar()
}
) { it ->
LazyColumn(contentPadding = it) {
items(dogs) {
DogItem(
dog = it,
modifier = Modifier.padding(dimensionResource(R.dimen.padding_small))
)
}
}
}
}
/**
* Composable that displays a list item containing a dog icon and their information.
*
* @param dog contains the data that populates the list item
* @param modifier modifiers to set to this composable
*/
@Composable
fun DogItem(
dog: Dog,
modifier: Modifier = Modifier
) {
var expanded by remember { mutableStateOf(false) }
val color by animateColorAsState(
targetValue = if (expanded) MaterialTheme.colorScheme.tertiaryContainer
else MaterialTheme.colorScheme.primaryContainer,
)
Card(
modifier = modifier
) {
Column(modifier = Modifier .animateContentSize(
animationSpec = spring(
dampingRatio = Spring.DampingRatioNoBouncy,
stiffness = Spring.StiffnessMedium
)
)
.backgroundColor(color=color)
){
Row(
modifier = Modifier
.fillMaxWidth()
.padding(dimensionResource(R.dimen.padding_small))
) {
DogIcon(dog.imageResourceId)
DogInformation(dog.name, dog.age)
Spacer(modifier = Modifier.weight(1f))
DogItemButton(
expanded = expanded,
onClick = { expanded = !expanded }
)
}
if (expanded) {
DogHobby(
dog.hobbies, modifier = Modifier.padding(
start = dimensionResource(R.dimen.padding_medium),
top = dimensionResource(R.dimen.padding_small),
end = dimensionResource(R.dimen.padding_medium),
bottom = dimensionResource(R.dimen.padding_medium)
)
)
}
}
}
}
@Composable
private fun DogItemButton(
expanded: Boolean,
onClick: () -> Unit,
modifier: Modifier = Modifier
){
IconButton(
onClick = onClick,
modifier = modifier
){
Icon(
imageVector = if (expanded) Icons.Filled.ExpandLess else Icons.Filled.ExpandMore,
contentDescription = stringResource(R.string.expand_button_content_description),
tint = MaterialTheme.colorScheme.secondary
)
}
}
@Composable
fun DogHobby(
@StringRes dogHobby: Int,
modifier: Modifier = Modifier
){
Column(
modifier = modifier
) {
Text(
text = stringResource(R.string.about),
style = MaterialTheme.typography.labelSmall
)
Text(
text = stringResource(dogHobby),
style = MaterialTheme.typography.bodyLarge
)
}
}
/**
* Composable that displays a Top Bar with an icon and text.
*
* @param modifier modifiers to set to this composable
*/
@Composable
fun WoofTopAppBar(modifier: Modifier = Modifier) {
CenterAlignedTopAppBar(
title = {
Row(
verticalAlignment = Alignment.CenterVertically
) {
Image(
modifier = Modifier
.size(dimensionResource(R.dimen.image_size))
.padding(dimensionResource(R.dimen.padding_small)),
painter = painterResource(R.drawable.ic_woof_logo),
// Content Description is not needed here - image is decorative, and setting a
// null content description allows accessibility services to skip this element
// during navigation.
contentDescription = null
)
Text(
text = stringResource(R.string.app_name),
style = MaterialTheme.typography.displayLarge
)
}
},
modifier = modifier
)
}
/**
* Composable that displays a photo of a dog.
*
* @param dogIcon is the resource ID for the image of the dog
* @param modifier modifiers to set to this composable
*/
@Composable
fun DogIcon(
@DrawableRes dogIcon: Int,
modifier: Modifier = Modifier
) {
Image(
modifier = modifier
.size(dimensionResource(R.dimen.image_size))
.padding(dimensionResource(R.dimen.padding_small))
.clip(MaterialTheme.shapes.small),
contentScale = ContentScale.Crop,
painter = painterResource(dogIcon),
// Content Description is not needed here - image is decorative, and setting a null content
// description allows accessibility services to skip this element during navigation.
contentDescription = null
)
}
/**
* Composable that displays a dog's name and age.
*
* @param dogName is the resource ID for the string of the dog's name
* @param dogAge is the Int that represents the dog's age
* @param modifier modifiers to set to this composable
*/
@Composable
fun DogInformation(
@StringRes dogName: Int,
dogAge: Int,
modifier: Modifier = Modifier
) {
Column(modifier = modifier) {
Text(
text = stringResource(dogName),
style = MaterialTheme.typography.displayMedium,
modifier = Modifier.padding(top = dimensionResource(R.dimen.padding_small))
)
Text(
text = stringResource(R.string.years_old, dogAge),
style = MaterialTheme.typography.bodyLarge
)
}
}
/**
* Composable that displays what the UI of the app looks like in light theme in the design tab.
*/
@Preview
@Composable
fun WoofPreview() {
WoofTheme(darkTheme = false) {
WoofApp()
}
}
/**
* Composable that displays what the UI of the app looks like in dark theme in the design tab.
*/
@Preview
@Composable
fun WoofDarkThemePreview() {
WoofTheme(darkTheme = true) {
WoofApp()
}
}
当我尝试在模拟器上运行应用程序时，出现以下错误：
Unresolved reference: background
他们没有指定我需要包含任何导入内容，那么我缺少什么？
您可以使用
backgroundimport androidx.compose.foundation.background