Android Kotlin-如何读取活动内部的NFC标签

Question

我在这里找到了一些关于使用Android阅读NFC标签的最近帖子。我得到的结论是，执行NFC读取动作会触发一个分离的意图。

那么第一个问题：在我的清单中列出意图过滤器是否必要？

<intent-filter>
<action android:name="android.nfc.action.NDEF_DISCOVERED" />

<category android:name="android.intent.category.DEFAULT" />

<data android:mimeType="text/plain" />

我认为这是没有必要的，因为我不想推出我的应用程序通过NFC标签事件，对吗？

第二个问题：我如何保持我的NFC阅读逻辑/功能与我的app/活动相关？

<uses-permission android:name="android.permission.NFC" />
<uses-feature android:name="android.hardware.nfc" android:required="true" />

mNfcAdapter = NfcAdapter.getDefaultAdapter(this)

 @Override
protected void onNewIntent(Intent intent) { 

    handleIntent(intent);
}

例如，在iOS中，在VC中需要时有一个简单的NFC会话。

Answer 1

正确，如果您只想在activity处于前台时接收标记，您可以在运行时为此注册。您要查找的是NFCADapter上的EnableForegroundDispatch方法。您可以为要筛选到的特定类型的标记注册PendingIntent，并且每当检测到标记时，您的活动将在onNewIntent()中接收Intent。

Kotlin提供了一个简单的示例，说明如果您只需要ISODEP兼容NFC标签，将会是什么样子：

override fun onResume() {
    super.onResume()

    NfcAdapter.getDefaultAdapter(this)?.let { nfcAdapter ->
        // An Intent to start your current Activity. Flag to singleTop
        // to imply that it should only be delivered to the current 
        // instance rather than starting a new instance of the Activity.
        val launchIntent = Intent(this, this.javaClass)
        launchIntent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP)

        // Supply this launch intent as the PendingIntent, set to cancel
        // one if it's already in progress. It never should be.
        val pendingIntent = PendingIntent.getActivity(
            this, 0, launchIntent, PendingIntent.FLAG_CANCEL_CURRENT
        )

        // Define your filters and desired technology types
        val filters = arrayOf(IntentFilter(ACTION_TECH_DISCOVERED))
        val techTypes = arrayOf(arrayOf(IsoDep::class.java.name))

        // And enable your Activity to receive NFC events. Note that there
        // is no need to manually disable dispatch in onPause() as the system
        // very strictly performs this for you. You only need to disable 
        // dispatch if you don't want to receive tags while resumed.
        nfcAdapter.enableForegroundDispatch(
            this, pendingIntent, filters, techTypes
        )
    }
}

override fun onNewIntent(intent: Intent) {
    super.onNewIntent(intent)

    if (NfcAdapter.ACTION_TECH_DISCOVERED == intent.action) {
        val tag = intent.getParcelableExtra<Tag>(NfcAdapter.EXTRA_TAG)
        IsoDep.get(tag)?.let { isoDepTag ->
            // Handle the tag here
        }
    }
}