kotlin集成retrofit获取网络数据，将数据通过Flow发射

效果：

1.定义实体类和网络相关

实体类：

package com.aruba.flowapplyapplication.model

data class Article(val id: Int, val text: String)

Api：

package com.aruba.flowapplyapplication.net

import com.aruba.flowapplyapplication.model.Article
import retrofit2.http.GET
import retrofit2.http.Query

/**
 * Created by aruba on 2021/9/21.
 */
interface Api {
    
    @GET("article")
    suspend fun searchArticles(
        @Query("key") key: String
    ): List<Article>
    
}

Retrofit的工具类：

package com.aruba.flowapplyapplication.net

import okhttp3.OkHttpClient
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

/**
 * Created by aruba on 2021/9/21.
 */
object RetrofitClient {
    private val instance: Retrofit by lazy {
        Retrofit.Builder()
            .baseUrl("http://192.168.0.118:8080/kotlinstudyserver/")
            .client(OkHttpClient.Builder().build())
            .addConverterFactory(GsonConverterFactory.create())
            .build()
    }

    fun getApi(): Api {
        return instance.create(Api::class.java)
    }
}

2.ViewModel实现

利用LiveData进行后续的双向绑定

package com.aruba.flowapplyapplication.viewmodel

import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import com.aruba.flowapplyapplication.model.Article
import com.aruba.flowapplyapplication.net.RetrofitClient
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.flowOn
import kotlinx.coroutines.launch

/**
 * Created by aruba on 2021/9/21.
 */
class ArticleViewModel : ViewModel() {
    var searchText: MutableLiveData<String> = MutableLiveData()
    var articleList = MutableLiveData<List<Article>>()

    fun getArticle() {
        if (searchText.value == null) return
        
        viewModelScope.launch {
            flow {
                emit(RetrofitClient.getApi().searchArticles(searchText.value!!))
            }.flowOn(Dispatchers.IO).catch { e ->
                e.printStackTrace()
            }.collect {
                articleList.value = it
            }
        }
    }
}

fragment的布局也比较简单，一个EditText和RecyclerView

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ArticleFragment">

        <androidx.appcompat.widget.AppCompatEditText
            android:id="@+id/appCompatEditText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:text="@={articleViewModel.searchText}"
            android:textSize="24sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerview"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_marginTop="10dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/appCompatEditText">

        </androidx.recyclerview.widget.RecyclerView>

    </androidx.constraintlayout.widget.ConstraintLayout>

    <data>

        <variable
            name="articleViewModel"
            type="com.aruba.flowapplyapplication.viewmodel.ArticleViewModel" />
    </data>
</layout>

3.在Fragment中进行绑定、配置等

package com.aruba.flowapplyapplication

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.lifecycleScope
import androidx.recyclerview.widget.LinearLayoutManager
import com.aruba.flowapplyapplication.adapter.ArticleAdapter
import com.aruba.flowapplyapplication.databinding.FragmentArticleBinding
import com.aruba.flowapplyapplication.viewmodel.ArticleViewModel
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.launch

class ArticleFragment : Fragment() {

    private val articleViewModel by lazy { ArticleViewModel() }

    private val articleAdapter by lazy { ArticleAdapter() }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val fragmentArticleBinding = DataBindingUtil.inflate<FragmentArticleBinding>(
            inflater,
            R.layout.fragment_article,
            container,
            false
        )

        //绑定viewmodel
        fragmentArticleBinding.articleViewModel = articleViewModel
        //配置recyclerview
        fragmentArticleBinding.recyclerview.adapter = articleAdapter
        fragmentArticleBinding.recyclerview.layoutManager = LinearLayoutManager(requireContext())

        //设置LiveData
        fragmentArticleBinding.lifecycleOwner = viewLifecycleOwner

        //对edittext文本进行监听
        articleViewModel.searchText.observe(viewLifecycleOwner) {
            articleViewModel.getArticle()
        }
        //对服务器返回list的变化进行监听
        articleViewModel.articleList.observe(viewLifecycleOwner) {
            articleAdapter.setData(it)
        }

        return fragmentArticleBinding.root
    }

}

Demo地址：https://gitee.com/aruba/flow-apply-application.git