基础使用：

DownloadManager.Request request;
try{
    request = new DownloadManager.Request(Uri.parse("String url"));
    // 放入下载队列
    Context appContext = getApplicationContext();
    DownloadManager manager = (DownloadManager)appContext.getSystemService(Context.DOWNLOAD_SERVICE);
    manager.enqueue(request);
}catch (Exception e){
    e.printStackTrace();
    return;
}

加入下载队列后可以获得一个下载ID用于创建下载进度观察者或者下载完成的广播通知

long downloadId = manager.enqueue(request);

下载进度观察者:

final DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
getContentResolver().registerContentObserver(Uri.parse("content://downloads/my_downloads"), true, new ContentObserver(new Handler()) {
    @Override
    public void onChange(boolean selfChange) {
        int[] bytesAndStatus = new int[]{-1, -1, 0};
        DownloadManager.Query query = new DownloadManager.Query().setFilterById(downloadId);
        Cursor cursor = null;
        try {
            cursor = dm.query(query);
            if (cursor != null && cursor.moveToFirst()) {
                //已经下载文件大小
                bytesAndStatus[0] = cursor.getInt(cursor.getColumnIndexOrThrow(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
                //下载文件的总大小
                bytesAndStatus[1] = cursor.getInt(cursor.getColumnIndexOrThrow(DownloadManager.COLUMN_TOTAL_SIZE_BYTES));
                //下载状态
                bytesAndStatus[2] = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS));
                //计算下载进度
                float progress = (float)bytesAndStatus[0]/bytesAndStatus[1];
                
                // 当进度完全执行好了记得 注销观察者 不注销的话 可能会多跑几次
                if(progress == 1){
                    getContentResolver().unregisterContentObserver(this);
                }
            }
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }
});

注册广播接收者

IntentFilter intentFilter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        long ID = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
        if (ID == downloadId) {
            // 执行完成后的代码
            Toast.makeText(getApplicationContext(), "任务:" + downloadId + " 下载完成!", Toast.LENGTH_LONG).show();
            // 记得注销广播接收者  不注销的话这个会一直在的
            unregisterReceiver(this);
        }
    }
};
registerReceiver(broadcastReceiver, intentFilter);

其他：

1.保存路径问题

request.setDestinationInExternalPublicDir("保存路径","保存的文件名称");

2.通知栏显示下载信息

request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
request.setTitle("下载");
request.setDescription("应用正在下载");
request.setAllowedOverRoaming(false);

3.个人使用目的：下载apk，完成后调用安装

String serviceString = Context.DOWNLOAD_SERVICE;
DownloadManager dManager = (DownloadManager) context.getSystemService(serviceString);
// 根据下载管理获取下载文件的URI 自己写Uri.pase("文件路径")也是可以的
Uri downloadFileUri = dManager.getUriForDownloadedFile(downloadId);
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION); // 该语句会授予临时的访问权限 否则会秒退
intent.setDataAndType(fileuri, "application/vnd.android.package-archive");
startActivity(intent);

查看原文： android 之 DownloadManager