Android 10中DownloadManager下载PDF后打开异常问题求助

问题现象 #

使用DownloadManager从服务器下载文件，通过BroadcastReceiver触发打开操作，在Android 12上运行正常，但Android 10中PDFViewer会先显示空白几秒，随后自动返回应用。

可能原因 #

1. 文件下载完成广播触发时，文件尚未完全写入磁盘，导致PDF阅读器读取失败
2. Android 10及以下版本中，临时Uri权限的授予机制存在差异，仅设置FLAG_GRANT_READ_URI_PERMISSION可能无法让第三方应用正常获取权限
3. 广播接收器注销时机过早，或者文件路径处理存在错误

解决方案 #

1. 修改下载完成后的处理逻辑 #

调整代码，确保文件写入完成后再打开，同时适配权限授予机制：

fun Activity.openLink(url: String) {
    val downloadmanager = getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager

    val fileName = "file.pdf"

    val request = DownloadManager.Request(Uri.parse(url))
        .setTitle("")
        .setDescription("")
        .setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED)
        .setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName)
    downloadmanager.enqueue(request)

    val onComplete: BroadcastReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            if (intent.action == DownloadManager.ACTION_DOWNLOAD_COMPLETE) {
                val downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0)
                val query = DownloadManager.Query().setFilterById(downloadId)
                // 使用use自动关闭Cursor，避免资源泄漏
                downloadmanager.query(query).use { cursor ->
                    if (cursor.moveToFirst()) {
                        val columnStatusIndex = cursor.getColumnIndex(DownloadManager.COLUMN_STATUS)
                        if (DownloadManager.STATUS_SUCCESSFUL == cursor.getInt(columnStatusIndex)) {
                            val columnUriIndex = cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI)
                            val localUri = Uri.parse(cursor.getString(columnUriIndex))
                            val file = File(localUri.path!!)

                            // 等待文件完全写入磁盘
                            waitForFileReady(file)

                            val uri = FileProvider.getUriForFile(context, "${BuildConfig.APPLICATION_ID}.fileprovider", file)
                            val target = Intent(Intent.ACTION_VIEW).apply {
                                setDataAndType(uri, "application/pdf")
                                addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
                                addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
                            }

                            // 给所有支持该Intent的应用手动授予读取权限（适配Android 10）
                            val resInfoList = context.packageManager.queryIntentActivities(target, PackageManager.MATCH_DEFAULT_ONLY)
                            resInfoList.forEach { resolveInfo ->
                                val packageName = resolveInfo.activityInfo.packageName
                                context.grantUriPermission(packageName, uri, Intent.FLAG_GRANT_READ_URI_PERMISSION)
                            }

                            startActivity(Intent.createChooser(target, ""))
                        }
                    }
                }
                // 处理完成后注销广播接收器，捕获重复注销异常
                try {
                    context.unregisterReceiver(this)
                } catch (e: IllegalArgumentException) {
                    e.printStackTrace()
                }
            }
        }

        // 等待文件可读取，最多等待5秒
        private fun waitForFileReady(file: File) {
            val maxWaitTime = 5000
            val checkInterval = 200
            var waitedTime = 0
            while (!file.canRead() && waitedTime < maxWaitTime) {
                Thread.sleep(checkInterval.toLong())
                waitedTime += checkInterval
            }
        }
    }

    registerReceiver(onComplete, IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE))
}

2. 统一FileProvider配置 #

确保AndroidManifest.xml中的authorities与代码一致，避免权限匹配失败：

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="${BuildConfig.APPLICATION_ID}.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true"
    tools:replace="android:authorities">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_provider_filepaths"
        tools:replace="android:resource" />
</provider>

3. 简化FileProvider路径配置 #

res/xml/file_provider_filepaths.xml无需重复配置外部存储路径，保留一条即可：

<?xml version="1.0" encoding="utf-8"?>
<paths>
    <external-path name="external_files" path="."/>
</paths>

修改说明 #

• 用use自动管理Cursor生命周期，避免资源泄漏
• 添加文件就绪等待逻辑，确保文件完全写入后再打开
• 手动给所有支持PDF查看的应用授予Uri读取权限，适配Android 10的权限规则
• 调整广播接收器注销时机，确保业务逻辑执行完成后再注销
• 统一FileProvider的authorities配置，避免权限不匹配

内容的提问来源于stack exchange，提问作者Rasul Mingazov