Kotlin collaboration process +flow download case

Import dependence

implementation "com.squareup.retrofit2:retrofit:2.9.0"
implementation "com.squareup.retrofit2:converter-gson:2.9.0"
implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.2.0"

// Extension method   Read / write file and return , Download progress 
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
}

sealed class DownloadStatus{
     data class Progress(val value:Int):DownloadStatus() // Return to download progress 
     data class Error(val throwable: Throwable):DownloadStatus() // A failure error is returned 
     data class Done(val file: File):DownloadStatus() // Return results 
}

This class is an enumeration class , It is the function of encapsulation

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() // Use OKHttp To make a network request 
            if (response.isSuccessful) { // Whether the request is successful 
                response.body()!!.let { body ->
                    val contentLength = body.contentLength()// Total length of downloaded content 

                    file.outputStream().use { output ->
                        val input = body.byteStream()
                        var emittedProcess = 0L
                        input.copyTo(output) { bytesCopied ->
                            val progress = bytesCopied * 100 / contentLength // Calculate download progress 
                            if (progress - emittedProcess > 5) {
                                delay(100)
                                emit(DownloadStatus.Progress(progress.toInt()))// Send download progress 
                                emittedProcess=progress
                            }
                        }
                    }
                }
                emit(DownloadStatus.Done(file)) // Return results 
            } else {
                throw  IOException(response.toString()) // No request succeeded in throwing an exception 
            }
        }.catch {
            file.delete()// Something goes wrong   Delete error file 
            emit(DownloadStatus.Error(it))// And return error 
        }.flowOn(Dispatchers.IO)// Switch child threads 
    }
}

Singleton class , Encapsulate download code .

class Fragmentb : Fragment() {
        val url:String="https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fclubimg.club.vmall.com%2Fdata%2Fattachment%2Fforum%2F202005%2F15%2F230954fsa0bsgqep8zu2j9.jpg&refer=http%3A%2F%2Fclubimg.club.vmall.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=jpeg?sec=1637312693&t=4d8c9a64de10cb68fb26d027a0ee4225"
    private val mBinding: FragmentFragmentbBinding by lazy {
        FragmentFragmentbBinding.inflate(layoutInflater)
    }
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return mBinding.root
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
                // This process and fragment Life cycle binding 
        lifecycleScope.launchWhenCreated {
        context?.apply {
                            //  External file directory path 
            val file=File(getExternalFilesDir(null)?.path,"pic.jpg")

              DownloadManager.download(url,file).collect {
                status->
                  when(status){
                      is DownloadStatus.Progress->{  // Download progress 
                          mBinding.apply {
                              progressBar.progress=status.value
                              tvProgress.text="${status.value}%"
                          }
                      }
                      is DownloadStatus.Error->{  // Download error 
                          Toast.makeText(context," Download error ",Toast.LENGTH_SHORT).show()
                      }
                      is DownloadStatus.Done->{  // Download complete 
                          mBinding.apply {
                              progressBar.progress=100
                              tvProgress.text="100&"
                          }
                          Toast.makeText(context," Download complete ",Toast.LENGTH_SHORT).show()
                      }else->{
                            Log.d("ning"," Download failed ")
                      }
                  }
              }
          }
        }
    }
}

stay fragment Quote and give UI feedback .

Effect demonstration :