从互联网获取数据

实例代码：https://github.com/google-developer-training/basic-android-kotlin-compose-training-mars-photos

添加权限 manifests/AndroidManifest.xml 文件

xml

    <uses-permission android:name="android.permission.INTERNET" />
    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApplication"
        tools:targetApi="31">
        ....
    </application>

添加依赖

implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")

network/MarsApiService.kt

java

package com.example.marsphotos.network

import com.jakewharton.retrofit2.converter.kotlinx.serialization.asConverterFactory
import kotlinx.serialization.json.Json
import okhttp3.MediaType.Companion.toMediaType
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.http.GET

private const val BASE_URL = "https://api.thecatapi.com/"

// 配置 Json 实例
val json = Json {
    ignoreUnknownKeys = true // 忽略未知字段
}

// 配置 Retrofit 实例
val retrofit: Retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(GsonConverterFactory.create())
    .build()

// 定义 API 服务接口
interface MarsApiService {
    @GET("v1/images/search?limit=10")
    suspend fun getPhotos(): List<MarsPhoto>
}

network/MarsApi.kt

java

package com.example.marsphotos.network

object MarsApi {
    val retrofitService : MarsApiService by lazy {
        retrofit.create(MarsApiService::class.java)
    }
}

network/MarsPhoto

java

package com.example.marsphotos.network

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class MarsPhoto(
    val id: String,
//    @SerialName("url") val imageUrl: String,
    val url: String,
    val width: Int,
    val height: Int
)

ui/screens/MarsViewModel.kt 调用

java

/*
 * 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.marsphotos.ui.screens

import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import com.example.marsphotos.network.MarsApi
import kotlinx.coroutines.launch
import java.io.IOException

sealed interface MarsUiState {
    data class Success(val photos: String) : MarsUiState
    object Error : MarsUiState
    object Loading : MarsUiState
}
class MarsViewModel : ViewModel() {
    /** The mutable State that stores the status of the most recent request */
//    var marsUiState: String by mutableStateOf("")
//        private set
    var marsUiState: MarsUiState by mutableStateOf(MarsUiState.Loading)
        private set

    /**
     * Call getMarsPhotos() on init so we can display status immediately.
     */
    init {
        getMarsPhotos()
    }

    /**
     * Gets Mars photos information from the Mars API Retrofit service and updates the
     * [MarsPhoto] [List] [MutableList].
     */
    fun getMarsPhotos() {
//        marsUiState = "Set the Mars API status response here!"
        viewModelScope.launch {
            marsUiState = try {
                val listResult = MarsApi.retrofitService.getPhotos()
                MarsUiState.Success("Success: ${listResult.size} Mars photos retrieved")
            } catch (e: IOException) {
                MarsUiState.Error
            }

        }
    }
}

从互联网获取数据 ​

从互联网获取数据