java - 如何从 url 下载 pdf 到内部存储并打开它 : Android studio using kotlin

Question

class Eco9 : AppCompatActivity() {

    lateinit internal var uri: Uri

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_eco9)
        this.getActionBar();
        this.supportActionBar!!.title = "Class 9th Economics";

        fab.setOnClickListener { view ->
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
        }
        supportActionBar?.setDisplayHomeAsUpEnabled(true)

       val openActivityDownload: Button = findViewById(R.id.eco9ch1)
        openActivityDownload.setOnClickListener {
            val s = "https://drive.google.com/file/d/0B71LXrqWr0mFUTk5WnVyVEQ3MFE/export?format=pdf"
            val fname = "123.pdf"
            if (FileExists(fname)) { previewpdf(fname) }
            else { download(s)
                Toast.makeText(applicationContext, "File will download", Toast.LENGTH_LONG).show()
            }
        }

    }

    fun FileExists(name: String): Boolean {
        val file = File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).path + separator + name)
        return file.exists()
    }

    private fun download(s: String) {
        val downloadManager = getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
        val uri = Uri.parse(s)
        val request = DownloadManager.Request(uri)
        val nameOfFile = URLUtil.guessFileName(uri.toString(), null, MimeTypeMap.getFileExtensionFromUrl(uri.toString()))
        val destinationInExternalPublicDir = request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS)
        request.setAllowedOverMetered(true)
        request.setAllowedOverRoaming(true)
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE)
        request.allowScanningByMediaScanner()
        downloadManager.enqueue(request)
    }

    private fun previewpdf(name: String) {
       val file = File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).path + separator + name)
       val path = fromFile(file)
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
        val intent = Intent(Intent.ACTION_VIEW, path)

        val chooser = Intent.createChooser(intent, "Open with")
        if (intent.resolveActivity(packageManager) != null)
            startActivity(chooser)
        else
            Toast.makeText(applicationContext, "No suitable application to open file", Toast.LENGTH_LONG).show()
    }
}

我想从给定的网址下载 pdf，我按下名为“echo9ch1”的按钮，如果内部公共(public)下载文件夹中不存在文件，则调用函数下载，否则如果存在，则应打开 pdf，而不是再次下载。我哪里失踪了？我可以打开之前下载的123.pdf。但我删除了我的 pdf 文件，并且下载功能现在无法使用。实际上，出现了一个小问题，因为我正在使用下载函数中的代码。请帮助我使用 download() 函数，并查看 Preview() 和 fileExists() 函数。我还在manifest.xml中添加了权限。我也想在没有wifi的情况下下载pdf。

list 权限是:

 <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

Answer 1

要下载，您必须使用异步任务。

就像在这个例子中一样，我正在下载多个文件，它可以是 PDF、图像等

class DownloadFileAsync(paths: Array<String?>, listener: AsyncResponse?, size: Int) : AsyncTask<String, String, Array<String?>>() {
    private val listener: AsyncResponse? = listener
    var current = 0
    var paths: Array<String?>
    val downPaths = arrayOfNulls<String>(size)

    lateinit var fpath: String
    var show = false


    init {
        this.paths = paths
    }


    protected override fun onPreExecute() {
        super.onPreExecute()
    }

    protected override fun doInBackground(vararg aurl: String): Array<String?> {
        val rows = aurl.size
        while (current < rows) {
            var count: Int
            try {
                println("Current: " + current + "\t\tRows: " + rows)
                fpath = getFileName(this.paths[current]!!)
                val url = URL(this.paths[current])
                val conexion = url.openConnection()
                conexion.connect()
                val lenghtOfFile = conexion.getContentLength()
                val input = BufferedInputStream(url.openStream(), 512)
                val file = File(Environment.getExternalStorageDirectory().path.plus(File.separator).plus(fpath))
                downPaths.set(current, file.absolutePath)
                if (!file.exists()) file.createNewFile()
                val output = FileOutputStream(file)
                val data = ByteArray(512)
                var total: Long = 0
                while (true) {
                    count = input.read(data)
                    if (count == -1) break
                    total += count
                    output.write(data, 0, count)
                }


                show = true
                output.flush()
                output.close()
                input.close()
                current++
            } catch (e: Exception) {
                Log.d("Exception", "" + e)
            }
        } // while end
        onPostExecute(downPaths)
        return downPaths
    }

    override fun onProgressUpdate(progress: Array<String?>) {

    }

    override fun onPostExecute(result: Array<String?>) {
        listener?.processFinish(result)
    }

    private fun getFileName(wholePath: String): String {
        var name: String? = null
        val start: Int
        val end: Int
        start = wholePath.lastIndexOf('/')
        end = wholePath.length //lastIndexOf('.');
        name = wholePath.substring((start + 1), end)
        return name
    }
}

之后我通过接口(interface)回调文件路径 监听器？.processFinish(结果)