File Kotlin，如何对从OnActivityResult返回的文件进行Base64编码

我需要制定逻辑，向电子邮件客户端添加附件。 我拥有所需的所有权限，并为文件创建了一个意图：

  val intent = Intent(Intent.ACTION_GET_CONTENT)
  intent.type = "*/*"
  activity?.startActivityForResult(intent, ActivityResultHandler.PICK_FILE)

我选择了一个文件，并在onActivityResult中得到结果ok：

public override fun onActivityResult(reqCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(reqCode, resultCode, data)
    ActivityResultHandler().onActivityResult(this, reqCode, resultCode, data)
    if (reqCode == REQUEST_CODE_SET_DEFAULT_DIALER) {
        activityToFragmentCommunicationCallback?.sendData("refresh")
    } else if (reqCode == ActivityResultHandler.PICK_FILE && resultCode == RESULT_OK && data != null) {
        val uri = data.data
        val cr = this.contentResolver
        val mime = cr.getType(uri)
        var file = uri.toFile()
        if (file.exists()) {
            var base64 = convertToBase64(file)
            DialogFullScreenEmailComposer.addAttachment()
        }
    }
}

但随后它崩溃了：

var file=uri.toFile（）

告诉我：

2019-09-18 16:12:12.300 20608-20608/com.xelion.android.debug E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.xelion.android.debug, PID: 20608
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=3, result=-1, data=Intent { dat=content://com.android.providers.downloads.documents/document/raw:/storage/emulated/0/Download/106.apk flg=0x1 }} to activity {com.xelion.android.debug/com.xelion.android.activity.MainActivity}: java.lang.IllegalArgumentException: Uri lacks 'file' scheme: content://com.android.providers.downloads.documents/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2F106.apk
    at android.app.ActivityThread.deliverResults(ActivityThread.java:4398)
    at android.app.ActivityThread.handleSendResult(ActivityThread.java:4440)
    at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6718)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.IllegalArgumentException: Uri lacks 'file' scheme: content://com.android.providers.downloads.documents/document/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2F106.apk
    at androidx.core.net.UriKt.toFile(Uri.kt:40)
    at com.xelion.android.activity.MainActivity.onActivityResult(MainActivity.kt:312)
    at android.app.Activity.dispatchActivityResult(Activity.java:7462)
    at android.app.ActivityThread.deliverResults(ActivityThread.java:4391)
    at android.app.ActivityThread.handleSendResult(ActivityThread.java:4440) 
    at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6718) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

---

如何才能创建我的文件？或者我可以跳过它，直接创建base64Encoded吗？

错误消息表明

Uri

没有指向文件（它不是以

file://

开头）。在较新的Android版本中，您无法直接访问所请求的文件，但可以通过

ContentResolver

读取其内容。您可以通过使用

cr.openInputStream（uri）

打开

InputStream

来实现这一点。当您拥有它时，您可以从该流中读取并将结果转换为Base64

下面是一个关于如何将文件的全部内容读入ByteArray的示例：

private fun readFile(cr: ContentResolver, uri: Uri): ByteArray {
    val inStream = cr.openInputStream(uri) ?: return ByteArray(0)
    val outStream = ByteArrayOutputStream()
    val buffer = ByteArray(32)
    while (inStream.read(buffer) > 0) {
        outStream.write(buffer)
    }
    return outStream.toByteArray()
}

先生，你是救世主