首先看一下效果：
使用方式：
fileUrl.setText("https://kotlinlang.org/docs/kotlin-docs.pdf") fileName.setText("Kotlin-Docs.pdf") downloadButton.setOnClickListener { DownLoadLaunch.create(this, fileUrl.text.toString(), fileName.text.toString(), object : OnStateListener { override fun start() { Toast.makeText(context, "开始下载", Toast.LENGTH_LONG).show() } override fun process(value: Int) { downloadButton.text = "Downloading $value" } override fun error(throwable: Throwable) { Toast.makeText(context, "下载出错：${throwable.message}", Toast.LENGTH_LONG).show() downloadButton.text = "DownLoad" } override fun donal(file: File) { downloadButton.text = "下载成功" downloadPath.setText(file.absolutePath) Toast.makeText(context, "下载完成：" + file.path, Toast.LENGTH_LONG).show() } }) }
只需要指定 url 和 文件的名字，在调用一个方法，就可以实现文件的下载。并且当前活动销毁时，就会停止下载
下面看一下使用方法：
1，导入依赖：
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8" implementation "androidx.core:core-ktx:1.2.0" //协程基础库 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.1" //协程 Android 库，提供 UI 调度器 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.1" //liveData + ViewModel + lifecycle implementation "androidx.lifecycle:lifecycle-livedata-core-ktx:2.3.0-alpha01" implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.3.0-alpha01" implementation "androidx.lifecycle:lifecycle-reactivestreams-ktx:2.3.0-alpha01" implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.3.0-alpha01" implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.0-alpha01"
2，创建 DownLoadManager
object DownLoadManager { //创建文件 private val downloadDirectory by lazy { File(ContextTools.context.filesDir, "download").also { it.mkdirs() } } //状态 sealed class DownloadStatus { object None : DownloadStatus() class Progress(val value: Int) : DownloadStatus() class Error(val throwable: Throwable) : DownloadStatus() class Donel(val file: File) : DownloadStatus() } //下载 fun download(url: String, fileName: String): Flow<DownloadStatus> { val file = File(downloadDirectory, fileName) 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 -> //总大小 val total = body.contentLength() //当前值 var emittedProcess = 0L file.outputStream().use { output -> body.byteStream().use { input -> input.copyTo(output) { bytesCopied -> //计算百分比 val progress = bytesCopied * 100 / total //当前的值大于上一次的就进行通知 if (progress - emittedProcess > 1) { //发射，外部的 collect 会执行 emit(DownloadStatus.Progress(progress.toInt())) emittedProcess = progress } } } } //下载完成 emit(DownloadStatus.Donel(file)) } } else { throw Exception(response.message) } }.catch { file.delete() emit(DownloadStatus.Error(it)) //保留最新的值 }.conflate() } }
//重写了一些copyTo 方法，增加了一个参数，用来回调下载进度 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 }
上面主要使用了 flow 进行下载，不了解的可以先百度一下
3,创建 DownloadModel ，用来进行下载
class DownloadModel : ViewModel() { val downloadStateLiveData = MutableLiveData<DownLoadManager.DownloadStatus>(DownLoadManager.DownloadStatus.None) suspend fun download(url: String, fileName: String) { DownLoadManager.download(url, fileName) .flowOn(Dispatchers.IO) .collect { //发送数据 downloadStateLiveData.value = it } } }
4，创建 DownloadLaunch，入口类，我们调用这个类的方法进行下载
interface OnStateListener { fun start() fun process(value: Int) fun error(throwable: Throwable) fun donal(file: File) } object DownLoadLaunch { private val mDownloadModel: DownloadModel = DownloadModel() fun create( owner: LifecycleOwner, url: String, fileName: String, stateListener: OnStateListener ) { //这里的 Lambda 会被多次调用，当 liveData 发送消息后 lambda会得到执行 mDownloadModel.downloadStateLiveData.observe(owner) { status -> when (status) { DownLoadManager.DownloadStatus.None -> { //启动协程 owner.lifecycleScope.launch { stateListener.start() //下载 mDownloadModel.download(url, fileName) } } is DownLoadManager.DownloadStatus.Progress -> { stateListener.process(status.value) } is DownLoadManager.DownloadStatus.Error -> { stateListener.error(status.throwable) } is DownLoadManager.DownloadStatus.Donel -> { stateListener.donal(status.file) } } } } }
5，进行使用
<androidx.appcompat.widget.LinearLayoutCompat 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" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:orientation="vertical"> <androidx.appcompat.widget.AppCompatEditText android:id="@+id/fileUrl" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="文件路径" android:paddingLeft="20dp" android:paddingRight="20dp" android:textColor="#000000" android:textSize="25sp" /> <androidx.appcompat.widget.AppCompatEditText android:id="@+id/fileName" android:layout_width="match_parent" android:layout_height="wrap_content" android:paddingLeft="20dp" android:layout_marginTop="20dp" android:paddingRight="20dp" android:hint="文件名字" android:textColor="#000000" android:textSize="25sp" /> <androidx.appcompat.widget.AppCompatButton android:id="@+id/downloadButton" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="DownLoad" android:layout_marginTop="20dp" android:textAllCaps="false" /> <androidx.appcompat.widget.AppCompatEditText android:id="@+id/downloadPath" android:layout_width="match_parent" android:layout_height="wrap_content" android:paddingLeft="20dp" android:paddingRight="20dp" android:textColor="#000000" android:layout_marginTop="20dp" android:textSize="25sp" android:textStyle="bold" /> </androidx.appcompat.widget.LinearLayoutCompat>
class DownLoadActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_down_load) init() } @SuppressLint("SetTextI18n") private fun init() { fileUrl.setText("https://kotlinlang.org/docs/kotlin-docs.pdf") fileName.setText("Kotlin-Docs.pdf") downloadButton.setOnClickListener { DownLoadLaunch.create(this, fileUrl.text.toString(), fileName.text.toString(), object : OnStateListener { override fun start() { Toast.makeText(context, "开始下载", Toast.LENGTH_LONG).show() } override fun process(value: Int) { downloadButton.text = "Downloading $value" } override fun error(throwable: Throwable) { Toast.makeText(context, "下载出错：${throwable.message}", Toast.LENGTH_LONG).show() downloadButton.text = "DownLoad" } override fun donal(file: File) { downloadButton.text = "下载成功" downloadPath.setText(file.absolutePath) Toast.makeText(context, "下载完成：" + file.path, Toast.LENGTH_LONG).show() } }) } } }
