为什么我收到IOException异常时，使NFC标签只读 [英] Why I'm getting IOException when making NFC tag read only

问题描述

我做的AsyncTasks doInBackground我NFC写作。当我写NdefRecord效果很好，但是当我试图让只读我得到IOException异常标记。这里是异常发生时code：

I'm doing my NFC writing in the AsyncTasks doInBackground. When I write NdefRecord it works well but when I'm trying to make tag read only I'm getting IOException. Here is the code where exception occurs:

  if (readOnly && !ndef.canMakeReadOnly()) {
        throw new NdefCantMakeReadOnlyException(R.string.cant_make_read_only);
    } else if (readOnly) {
        ndef.makeReadOnly(); //IOException
    }

这makeReadOnly适用于超轻的Mifare（MF0ICU1）标签。

This makeReadOnly works with Mifare Ultralight (MF0ICU1) tags.

推荐答案

浏览通过Android 4.4.2源（我没有与旧版本检查）显示，你总是会得到一个 IOException异常如果 makeReadOnly（）失败，无论出于何种原因。所以，你发现了一个bug在Android或至少与API文档不匹配。

Browsing through the Android 4.4.2 source (I did not check with older versions) reveals that you will always get an IOException if makeReadOnly() fails for whatever reason. So you found a bug in Android or at least a mismatch with the API documentation.

原因是 android.nfc.tech.Ndef （见<一href=\"https://android.googlesource.com/platform/frameworks/base/+/android-4.4.2_r1/core/java/android/nfc/tech/Ndef.java\"相对=nofollow>此处，开始在线383）预计NFC的服务来回报错误codes.SUCCESS 成功锁定，错误codes.ERROR_INVALID_PARAM 失败的锁定和错误codes.ERROR_IO 上的任何IO相关的错误。但是，如果锁定成功的NFC服务将返回错误codes.SUCCESS（见<一href=\"https://android.googlesource.com/platform/packages/apps/Nfc/+/android-4.4.2_r1/src/com/android/nfc/NfcService.java\"相对=nofollow>这里，线路1438）和错误codes.ERROR_IO如果锁定任何原因而失败（请参阅这里，行1440）。 错误codes.ERROR_INVALID_PARAM 似乎并没有被所有返回，因此 makeReadOnly（）方法通常应该永远返回假。

The cause is that android.nfc.tech.Ndef (see here, starting on line 383) expects the NFC service to return ErrorCodes.SUCCESS for successful locking, ErrorCodes.ERROR_INVALID_PARAM for failed locking and ErrorCodes.ERROR_IO on any IO related error. However, the NFC service returns ErrorCodes.SUCCESS if locking succeeds (see here, line 1438) and ErrorCodes.ERROR_IO if locking fails for any reason (see here, line 1440). ErrorCodes.ERROR_INVALID_PARAM seems not to be returned at all, thus the makeReadOnly() method should typically never return false.

这篇关于为什么我收到IOException异常时，使NFC标签只读的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！