如何使用NFC扫描标签？

Question

我只是试图阅读标签的内容。但是我研究这个的时间越长，我越觉得它是唯一不了解它如何工作的人。

通过developer.android.com现场看，我发现了以下方法：

public String readTag(Tag tag) { 
     MifareUltralight mifare = MifareUltralight.get(tag); 
     try { 
      mifare.connect(); 
      byte[] payload = mifare.readPages(4); 
      return new String(payload, Charset.forName("US-ASCII")); 
     } catch (IOException e) { 
      Log.e(TAG, "IOException while writing Scanner message...", e); 
     } finally { 
      if (mifare != null) { 
       try { 
        mifare.close(); 
       } 
       catch (IOException e) { 
        Log.e(TAG, "Error closing tag...", e); 
       } 
      } 
     } 
     return null; 
    } 

现在我才可以使用，我需要初始化一些东西：

public void configScanner() 
    { 
     Intent intent = getIntent(); 
     tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG); 
     pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0); 
     ndef = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED); 
     try { 
      ndef.addDataType("*/*"); /* Handles all MIME based dispatches. You should specify only the ones that you need. */ 
     } 
     catch (MalformedMimeTypeException e) { 
      throw new RuntimeException("fail", e); 
     } 
     intentFiltersArray = new IntentFilter[] {ndef, }; 
     techListsArray = new String[][] { new String[] { Ndef.class.getName() } }; 
    } 

然后我只需尝试执行它。

public void scanClick(View v) 
{ 
    textview1.setText(readTag(tag)); 
} 

我还添加在清单的一些东西和我自己的XML文件

清单：

<intent-filter> 
    <action android:name="android.nfc.action.TECH_DISCOVERED"/> 
</intent-filter> 
<meta-data android:name="android.nfc.action.TECH_DISCOVERED" 
      android:resource="@xml/scan" /> 

scan.xml

<?xml version="1.0" encoding="UTF-8"?> 
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2"> 
    <tech-list> 
     <tech>android.nfc.tech.IsoDep</tech> 
     <tech>android.nfc.tech.NfcA</tech> 
     <tech>android.nfc.tech.NfcB</tech> 
     <tech>android.nfc.tech.NfcF</tech> 
     <tech>android.nfc.tech.NfcV</tech> 
     <tech>android.nfc.tech.Ndef</tech> 
     <tech>android.nfc.tech.NdefFormatable</tech> 
     <tech>android.nfc.tech.MifareClassic</tech> 
     <tech>android.nfc.tech.MifareUltralight</tech> 
    </tech-list> 
</resources> 

然而，当我执行我执行readTag(tag)时出现代码崩溃。我只是不明白如何让这些东西起作用。

所要求：一logcat的输出：

04-11 17:13:07.650: E/AndroidRuntime(672): FATAL EXCEPTION: main 
04-11 17:13:07.650: E/AndroidRuntime(672): java.lang.IllegalStateException: Could not execute method of the activity 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.view.View$1.onClick(View.java:3591) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.view.View.performClick(View.java:4084) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.view.View$PerformClick.run(View.java:16966) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.os.Handler.handleCallback(Handler.java:615) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.os.Handler.dispatchMessage(Handler.java:92) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.os.Looper.loop(Looper.java:137) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.app.ActivityThread.main(ActivityThread.java:4745) 
04-11 17:13:07.650: E/AndroidRuntime(672): at java.lang.reflect.Method.invokeNative(Native Method) 
04-11 17:13:07.650: E/AndroidRuntime(672): at java.lang.reflect.Method.invoke(Method.java:511) 
04-11 17:13:07.650: E/AndroidRuntime(672): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
04-11 17:13:07.650: E/AndroidRuntime(672): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
04-11 17:13:07.650: E/AndroidRuntime(672): at dalvik.system.NativeStart.main(Native Method) 
04-11 17:13:07.650: E/AndroidRuntime(672): Caused by: java.lang.reflect.InvocationTargetException 
04-11 17:13:07.650: E/AndroidRuntime(672): at java.lang.reflect.Method.invokeNative(Native Method) 
04-11 17:13:07.650: E/AndroidRuntime(672): at java.lang.reflect.Method.invoke(Method.java:511) 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.view.View$1.onClick(View.java:3586) 
04-11 17:13:07.650: E/AndroidRuntime(672): ... 11 more 
04-11 17:13:07.650: E/AndroidRuntime(672): Caused by: java.lang.NullPointerException 
04-11 17:13:07.650: E/AndroidRuntime(672): at android.nfc.tech.MifareUltralight.get(MifareUltralight.java:94) 
04-11 17:13:07.650: E/AndroidRuntime(672): at com.example.android_test.MainActivity.readTag(MainActivity.java:108) 
04-11 17:13:07.650: E/AndroidRuntime(672): at com.example.android_test.MainActivity.scanClick(MainActivity.java:155) 
04-11 17:13:07.650: E/AndroidRuntime(672): ... 14 more 

Answer 1

我没有看到这个在你发布清单的一部分，但你真的需要它。

添加到您的清单

<uses-permission android:name="android.permission.NFC" />