Tag

public final class Tag
extends Object implements Parcelable

java.lang.Object
↳	android.nfc.Tag

---

代表已发现的NFC标签。

Tag是一个不可变的对象，表示发现时NFC标签的状态。 它可以用作TagTechnology类的句柄来执行高级操作，或者通过getId()和它通过getTechList()包含的一组技术直接查询其ID。 传递给这个类并返回的数组不会被克隆，因此请小心不要修改它们。

每当标签被发现时（即使它是相同的物理标签），都会创建一个新的标签对象。 如果标签被移除并返回到范围内，则只有最近的标签对象才能成功用于创建TagTechnology 。

Tag Dispatch

When a tag is discovered, a Tag object is created and passed to a single activity via the EXTRA_TAG extra in an Intent via startActivity(Intent). A four stage dispatch is used to select the most appropriate activity to handle the tag. The Android OS executes each stage in order, and completes dispatch as soon as a single matching activity is found. If there are multiple matching activities found at any one stage then the Android activity chooser dialog is shown to allow the user to select the activity to receive the tag.

标签调度机制被设计为给标签分配正确的活动的概率高，而不会向用户显示活动选择器对话框。 这对于NFC交互非常重要，因为它们非常短暂 - 如果用户必须移动Android设备才能选择应用程序，那么连接可能会中断。

1. Foreground activity dispatch

A foreground activity that has called NfcAdapter.enableForegroundDispatch() is given priority. See the documentation on NfcAdapter.enableForegroundDispatch() for its usage.

2. NDEF data dispatch

If the tag contains NDEF data the system inspects the first NdefRecord in the first NdefMessage. If the record is a URI, SmartPoster, or MIME data startActivity(Intent) is called with ACTION_NDEF_DISCOVERED. For URI and SmartPoster records the URI is put into the intent's data field. For MIME records the MIME type is put in the intent's type field. This allows activities to register to be launched only when data they know how to handle is present on a tag. This is the preferred method of handling data on a tag since NDEF data can be stored on many types of tags and doesn't depend on a specific tag technology. See ACTION_NDEF_DISCOVERED for more detail. If the tag does not contain NDEF data, or if no activity is registered for ACTION_NDEF_DISCOVERED with a matching data URI or MIME type then dispatch moves to stage 3.

3. Tag Technology dispatch

startActivity(Intent) is called with ACTION_TECH_DISCOVERED to dispatch the tag to an activity that can handle the technologies present on the tag. Technologies are defined as sub-classes of TagTechnology, see the package android.nfc.tech. The Android OS looks for an activity that can handle one or more technologies in the tag. See ACTION_TECH_DISCOVERED for more detail.

4. Fall-back dispatch

If no activity has been matched then startActivity(Intent) is called with ACTION_TAG_DISCOVERED. This is intended as a fall-back mechanism. See ACTION_TAG_DISCOVERED.

NFC Tag Background

An NFC tag is a passive NFC device, powered by the NFC field of this Android device while it is in range. Tag's can come in many forms, such as stickers, cards, key fobs, or even embedded in a more sophisticated device.

标签可以具有广泛的功能。 简单标签只提供读/写语义，并包含一些一次性可编程区域以实现只读。 更复杂的标签提供数学运算和每个扇区的访问控制和认证。 最复杂的标签包含允许与标签上执行的代码进行复杂交互的操作环境。 使用TagTechnology类可以访问NFC标签中可用的各种功能。

Summary

Inherited constants
From interface android.os.Parcelable int CONTENTS_FILE_DESCRIPTOR 与 describeContents()使用的描述符位：表示 describeContents()对象的展平表示包含文件描述符。 int PARCELABLE_WRITE_RETURN_VALUE 用于 writeToParcel(Parcel, int)标志：正在写入的对象是返回值，即“ Parcelable someFunction() ”，“ void someFunction(out Parcelable) ”或“ void someFunction(inout Parcelable) ”等函数的结果。

Fields
public static final Creator<Tag>	CREATOR

Public methods
int	describeContents() 描述此Parcelable实例的封送表示中包含的特殊对象的种类。
byte[]	getId() 获取标签标识符（如果有的话）。
String[]	getTechList() 获取此标记中可用的技术，作为完全限定的类名称。
String	toString() 用于调试的标签的人类可读描述。
void	writeToParcel(Parcel dest, int flags) 将此对象平铺到一个包裹中。

Inherited methods
From class java.lang.Object Object clone() 创建并返回此对象的副本。 boolean equals(Object obj) 指示其他某个对象是否“等于”这一个。 void finalize() 当垃圾收集确定没有更多对该对象的引用时，由对象上的垃圾回收器调用。 final Class<?> getClass() 返回此 Object的运行时类。 int hashCode() 返回对象的哈希码值。 final void notify() 唤醒正在等待该对象监视器的单个线程。 final void notifyAll() 唤醒在该对象监视器上等待的所有线程。 String toString() 返回对象的字符串表示形式。 final void wait(long millis, int nanos) 导致当前线程等待，直到另一个线程调用此对象的 notify()方法或 notifyAll()方法，或者某个其他线程中断当前线程，或者经过一定的实时时间。 final void wait(long millis) 导致当前线程等待，直到另一个线程调用此对象的 notify()方法或 notifyAll()方法或经过了指定的时间量。 final void wait() 导致当前线程等待，直到另一个线程调用此对象的 notify()方法或 notifyAll()方法。
From interface android.os.Parcelable abstract int describeContents() 描述此Parcelable实例的封送表示中包含的特殊对象的种类。 abstract void writeToParcel(Parcel dest, int flags) 将此对象平铺到一个包裹中。

Fields

Public methods