使用Android自带的DownloadManager下载文件

- 简介
- 基础用法
  - 完整代码

先放Google官方文档：https://developer.android.google.cn/reference/android/app/DownloadManager

简介

使用Context.getSystemService(Context.DOWNLOAD_SERVICE)来获取DownloadManager的实例
DownloadManager可以将指定文件下载到指定位置，并处理下载出错、网络变化、系统重启等情况
需要注册一个ACTION_NOTIFICATION_CLICKED的Receiver来监听处理用户点击下载通知的事件

基础用法

首先保证应用具有android.permission.INTERNET权限。
注册一个BroadcastReceiver，并在intent-filter标签中添加名称为android.intent.action.DOWNLOAD_COMPLETE和android.intent.action.DOWNLOAD_NOTIFICATION_CLICKED的action。
使用DownloadManager.Request类构建一个下载请求，并使用DownloadManager.enqueue(request)方法开始进行下载。这个方法会返回一个long类型的值，标记了本次下载的id。

val request = DownloadManager.Request(uri)mId = mDownloadManager.enqueue(request)

下载完成后或用户点击通知栏的下载信息时，之前注册的Receiver会收到消息，我们在onReceive中进行处理。
开始下载之后，我们可以构建一个DownloadManager.Query对象，通过Query.setFilterById设置第3步中获取到的id，并调用DownloadManager.query方法进行查询。query方法返回一个Cursor，和ContentProvider使用方法相同。事实上，DownloadManager的查询就是使用CotentProvider实现的。

val query = DownloadManager.Query()query.setFilterById(mId)val c = mDownloadManager.query(query)c.moveToFirst()val soFar = c.getLong(c.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR))val total = c.getLong(c.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES))c.close()val currentSpeed = calSpeed()val speed = Util.byte2Human(currentSpeed)Log.d(TAG, "已下载大小: ${Util.byte2Human(soFar)} / ${Util.byte2Human(total)} \t 下载速度: $speed/s")

完整代码

为方便阅读，所有代码都放在了一个Activity中。功能很简单，就是下载一个网络文件，并打印出下载进度，并在下载结束之后进行处理。csdn编辑器对kotlin支持不是很好啊！

package top.littlefogcat.testdownloadimport android.app.Activityimport android.app.DownloadManagerimport android.app.DownloadManager.ACTION_DOWNLOAD_COMPLETEimport android.content.BroadcastReceiverimport android.content.Contextimport android.content.Intentimport android.content.IntentFilterimport android.net.Uriimport android.os.Bundleimport android.os.SystemClockimport android.util.Logimport kotlinx.android.synthetic.main.activity_test.*import java.util.*class TestActivity : Activity() {    companion object {        const val TAG = "TestActivity"    }    private lateinit var mDownloadManager: DownloadManager    private lateinit var mDownloadReceiver: DownloadReceiver    private var mId: Long = -1    private var mComplete = false    override fun onCreate(savedInstanceState: Bundle?) {        super.onCreate(savedInstanceState)        setContentView(R.layout.activity_test)        mDownloadManager = getSystemService(DOWNLOAD_SERVICE) as DownloadManager        btnDownload.setOnClickListener {            val url = Uri.parse(Constant.QQ_APK_URL)            val request = DownloadManager.Request(url)            mId = mDownloadManager.enqueue(request)            mDownloadReceiver = DownloadReceiver()            val filter = IntentFilter(ACTION_DOWNLOAD_COMPLETE)            registerReceiver(mDownloadReceiver, filter)            Thread(DownloadListener()).start()        }    }    fun notifyDownloadComplete(id: Long) {        mComplete = true        if (mId == -1L) {            Log.w(TAG, "notifyDownloadComplete: NO ID")            return        }        val query = DownloadManager.Query()        query.setFilterById(mId)        val c = mDownloadManager.query(query)        c.moveToFirst()        val localUri = c.getString(c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI))        val mediaType = c.getString(c.getColumnIndex(DownloadManager.COLUMN_MEDIA_TYPE))        Log.d(TAG, "notifyDownloadComplete: localUri = $localUri")        Log.d(TAG, "notifyDownloadComplete: mediaType = $mediaType")    }    override fun onDestroy() {        super.onDestroy()        unregisterReceiver(mDownloadReceiver)    }    private inner class DownloadListener : Runnable {        private val DEFAULT_QUEUE_SIZE = 5        private val mSpeedQueue = LinkedList()        override fun run() {            while (true) {                if (mComplete) {                    break                }                val query = DownloadManager.Query()                query.setFilterById(mId)                val c = mDownloadManager.query(query)                c.moveToFirst()                val soFar = c.getLong(c.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR))                val total = c.getLong(c.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES))                c.close()                if (mSpeedQueue.size >= DEFAULT_QUEUE_SIZE) {                    mSpeedQueue.poll()                    mSpeedQueue.offer(soFar)                } else {                    mSpeedQueue.offer(soFar)                }                val currentSpeed = calSpeed()                val speed = Util.byte2Human(currentSpeed)                Log.d(TAG, "已下载大小: ${Util.byte2Human(soFar)} / ${Util.byte2Human(total)} \t 下载速度: $speed/s")                SystemClock.sleep(500)            }        }        private fun calSpeed(): Long {            val size = mSpeedQueue.size            if (size < 2) {                return 0            }            return ((mSpeedQueue.last - mSpeedQueue.first) / (size - 1))        }    }    private inner class DownloadReceiver : BroadcastReceiver() {        override fun onReceive(context: Context?, intent: Intent?) {            Log.d(TAG, "onReceive: ${intent?.action}")            val id = intent?.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1)            id?.let { notifyDownloadComplete(it) }        }    }}

简介

基础用法

完整代码

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