使用Android自带的DownloadManager下载文件

傷城~ 2022-05-20 00:19 736阅读 0赞

*   *  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][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 ##

1.  首先保证应用具有`android.permission.INTERNET`权限。
2.  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。
3.  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)

1.  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。
2.  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.testdownload
    
    import android.app.Activity
    import android.app.DownloadManager
    import android.app.DownloadManager.ACTION_DOWNLOAD_COMPLETE
    import android.content.BroadcastReceiver
    import android.content.Context
    import android.content.Intent
    import android.content.IntentFilter
    import android.net.Uri
    import android.os.Bundle
    import android.os.SystemClock
    import android.util.Log
    import 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<Long>()
    
            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) }
            }
    
        }
    }

[https_developer.android.google.cn_reference_android_app_DownloadManager]: https://developer.android.google.cn/reference/android/app/DownloadManager