Android nfcv.transceive() 抛出异常

Question

我编写了一个 Android 应用程序，它使用 transceive() 函数与 NFC-V 卡进行通信。我的问题是那条线

byte[] response = nfcv.transceive(command)

总是抛出标签丢失异常。

有人可以帮我吗？

String action = intent.getAction();

Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
NfcV nfcv = NfcV.get(tag);
if(nfcv != null) {
    Toast.makeText(this, "nfcv detected", Toast.LENGTH_LONG).show();
}

try {
    nfcv.connect();
    Toast.makeText(this, "connected", Toast.LENGTH_LONG).show();
    byte[] command = new byte[]{                      
            (byte) 0x00, // Flags
            (byte) 0x20, // Command: Read single block
            (byte) 0x00, // First block (offset)
            (byte) 0x04  // Number of blocks};
    byte[] response = nfcv.transceive(command);
    nfcv.close();
} catch(Exception e) {
    Toast.makeText(this, "Error exception!", Toast.LENGTH_LONG).show();
}

我得到以下异常:

android.nfc.TagLostException: Tag was lost.
    at android.nfc.TransceiveResult.getResponseOrThrow(TransceiveResult.java:48)
    at android.nfc.tech.BasicTagTechnology.transceive(BasicTagTechnology.java:151)
    at android.nfc.tech.NfcV.transceive(NfcV.java:115)
    at com.example.nxf07589.nfc.MainActivity.onCreate(MainActivity.java:148)
    at android.app.Activity.performCreate(Activity.java:6374)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2767)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2879)
    at android.app.ActivityThread.access$900(ActivityThread.java:182)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1475)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:145)
    at android.app.ActivityThread.main(ActivityThread.java:6141)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

Answer 1

您收到 TagLostException，因为您的命令格式错误，因此标签没有响应。

正如其名称所示，READ SINGLE BLOCK 命令(命令代码 0x20)读取单个 block 。因此，此命令中没有长度(“ block 数”)字段。正确的命令应该是这样的:

int blockAddress = 0;
byte[] cmd = new byte[] {
        (byte) 0x00,  // FLAGS
        (byte) 0x20,  // READ_SINGLE_BLOCK
        (byte)(blockAddress & 0x0ff)
};
byte[] response = nfcv.transceive(cmd);

请注意，如果标签不理解该命令(READ SINGLE BLOCK 是 ISO/IEC 15693 中的可选命令)，您仍然可能会遇到 TagLostException。

最后，某些 Android 平台无法正常运行(或根本不支持)NFC-V 的未寻址命令。因此，您可能希望改用该命令的寻址形式:

byte[] tagUid = tag.getId();  // store tag UID for use in addressed commands

int blockAddress = 0;
byte[] cmd = new byte[] {
        (byte)0x20,  // FLAGS
        (byte)0x20,  // READ_SINGLE_BLOCK
        0, 0, 0, 0, 0, 0, 0, 0,
        (byte)(blockAddress & 0x0ff)
};
System.arraycopy(tagUid, 0, cmd, 2, 8);  // paste tag UID into command
byte[] response = nfcv.transceive(cmd);