Jetpack Compose-文件下载

前言

本文主要是文件的同步下载，结合flow实现线程的切换。

下载工具类

下载文件到临时目录

import android.content.Context
import java.io.File
import java.io.FileOutputStream
import java.net.HttpURLConnection
import java.net.URL

object ZFileDownloadUtils {
    fun downloadFileToTempFolder(
        context: Context,
        fileUrl: String,
        suffix: String = ".jpg"
    ): String? {
        var filePath: String? = null
        var mSuffix = suffix
        try {
            // 创建 URL 对象
            val url = URL(fileUrl)
            // 打开连接
            val connection = url.openConnection() as HttpURLConnection
            // 设置请求方法
            connection.requestMethod = "GET"

            if (fileUrl.contains(".")) {
                mSuffix = fileUrl.substring(fileUrl.lastIndexOf("."))
            }

            // 获取响应码
            val responseCode = connection.responseCode
            if (responseCode == HttpURLConnection.HTTP_OK) {
                // 获取输入流
                val inputStream = connection.inputStream

                // 创建临时文件
                val tempFile = File.createTempFile("downloaded_file", mSuffix, context.cacheDir)
                filePath = tempFile.absolutePath

                // 创建文件输出流
                val outputStream = FileOutputStream(tempFile)

                // 缓冲区大小
                val buffer = ByteArray(4096)
                var bytesRead: Int
                // 从输入流读取数据并写入输出流
                while (inputStream.read(buffer).also { bytesRead = it } != -1) {
                    outputStream.write(buffer, 0, bytesRead)
                }

                // 关闭流
                outputStream.close()
                inputStream.close()
            }
            // 断开连接
            connection.disconnect()
        } catch (e: Exception) {
            e.printStackTrace()
        }
        return filePath
    }
}

调用

viewModel中

fun downloadFile(context: Context, fileUrl: String) {
    viewModelScope.launch {
        flow {
            val filePath = ZFileDownloadUtils.downloadFileToTempFolder(context, fileUrl)
            emit(filePath)
        }
        .flowOn(Dispatchers.IO)
        .collect { 
            result ->
            Log.i(TAG, "downloadFile: $result")
        }
    }
}

Compose中

val context = LocalContext.current
LaunchedEffect(Unit) {
    vm.downloadFile(context, CommonData.fileShowUrl + vm.imgUrl.value)
}