学习了kotlin后，我们将它运用到实际开发中，结合Flow实现文件下载
最终效果：
项目使用了Navigation框架：Activity+Fragment的方式
导入依赖：
implementation 'androidx.navigation:navigation-fragment-ktx:2.3.5'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.5'
implementation 'androidx.legacy:legacy-support-v4:1.0.0'
//依赖协程核心库 ，提供Android UI调度器
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.1"
//依赖当前平台所对应的平台库 (必须)
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.5.1'
implementation 'com.squareup.retrofit2:retrofit:2.9.0'
并启用DataBinding
dataBinding {
enabled = true
}
fragment的创建、Navigation Graph的连接等操作就不介绍了
1.首先实现下载工具类，包含状态和下载实现
使用密封类定义状态：
package com.aruba.flowapplyapplication.download
import java.io.File
/**
* 下载状态
* Created by aruba on 2021/9/19.
*/
sealed class DownloadStatus {
data class Progress(val progress: Int) : DownloadStatus()
data class Err(val t: Throwable) : DownloadStatus()
data class Done(val file: File) : DownloadStatus()
}
静态方法方式定义下载管理类：
package com.aruba.flowapplyapplication.download
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.flow
import okhttp3.OkHttpClient
import okhttp3.Request
import java.io.File
import com.dongnaoedu.flowpractice.utils.copyTo
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.flowOn
import okhttp3.Dispatcher
import java.io.IOException
/**
* Created by aruba on 2021/9/19.
*/
object DownloadManager {
fun download(url: String, file: File): Flow<DownloadStatus> {
return flow {
val request = Request.Builder().url(url).get().build();
val response = OkHttpClient.Builder().build().newCall(request).execute()
if (response.isSuccessful) {
response.body()!!.let { body ->
//文件大小
val totalLength = body.contentLength().toDouble()
//写文件
file.outputStream().run {
val input = body.byteStream()
input.copyTo(this) { currentLength ->
//当前下载进度
val process = currentLength / totalLength * 100
emit(DownloadStatus.Progress(process.toInt()))
}
}
emit(DownloadStatus.Done(file))
}
} else {
throw IOException(response.toString())
}
}.catch {
file.delete()
emit(DownloadStatus.Err(it))
}.flowOn(Dispatchers.IO)
}
}
为InputStream添加扩展函数，实现字节拷贝：
package com.dongnaoedu.flowpractice.utils
import java.io.InputStream
import java.io.OutputStream
inline fun InputStream.copyTo(out: OutputStream, bufferSize: Int = DEFAULT_BUFFER_SIZE, progress: (Long)-> Unit): Long {
var bytesCopied: Long = 0
val buffer = ByteArray(bufferSize)
var bytes = read(buffer)
while (bytes >= 0) {
out.write(buffer, 0, bytes)
bytesCopied += bytes
bytes = read(buffer)
progress(bytesCopied)
}
return bytesCopied
}
2.定义ViewModel
使用LiveData定义进度属性，并实现下载按钮的点击事件，由于Flow的collect函数为挂起函数，需要使用协程作用域，我们直接使用viewModelScope：
package com.aruba.flowapplyapplication.viewmodel
import android.app.Application
import android.content.Context
import android.util.Log
import android.view.View
import android.widget.Toast
import androidx.lifecycle.*
import com.aruba.flowapplyapplication.download.DownloadManager
import com.aruba.flowapplyapplication.download.DownloadStatus
import com.aruba.flowapplyapplication.download.DownloadStatus.Progress
import kotlinx.coroutines.MainScope
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.launch
import java.io.File
/**
* Created by aruba on 2021/9/19.
*/
class DownloadViewModel(val context: Application) : AndroidViewModel(context) {
private var progressData = MutableLiveData<Int>()
val progress = progressData
private val url: String = "http://10.254.219.178:8080/test.rar"
fun downloadClick(v: View) {
viewModelScope.launch {
progressData.value = 0
val file = File(context.getExternalFilesDir(null), "test.rar")
DownloadManager.download(url, file).collect {
when (it) {
is Progress -> {
Log.i("progress", "progress: $it.progress")
progressData.value = it.progress
}
is DownloadStatus.Done -> {
progressData.value = 100
Toast.makeText(context, "下载完成", Toast.LENGTH_SHORT).show()
}
is DownloadStatus.Err ->
Toast.makeText(context, it.toString(), Toast.LENGTH_SHORT).show()
}
}
}
}
}
3.DataBinding和ViewModel绑定
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.ViewModelProvider
import androidx.lifecycle.lifecycleScope
import com.aruba.flowapplyapplication.databinding.FragmentFlowDownBinding
import com.aruba.flowapplyapplication.viewmodel.DownloadViewModel
class FlowDownloadFragment : Fragment() {
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val fragmentFlowDownBinding = DataBindingUtil.inflate<FragmentFlowDownBinding>(
layoutInflater,
R.layout.fragment_flow_down,
container,
false
)
val downloadViewModel = ViewModelProvider(
this,
ViewModelProvider.AndroidViewModelFactory(requireActivity().application)
).get(DownloadViewModel::class.java)
fragmentFlowDownBinding.downloadViewModel = downloadViewModel
fragmentFlowDownBinding.lifecycleOwner = this;
return fragmentFlowDownBinding.root
}
}
文件下载就完成了，代码量相比Java可以自行感受下
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