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NdefMessage

public final class NdefMessage
extends Object implements Parcelable

java.lang.Object
   ↳ android.nfc.NdefMessage


Represents an immutable NDEF Message.

NDEF (NFC Data Exchange Format) is a light-weight binary format, used to encapsulate typed data. It is specified by the NFC Forum, for transmission and storage with NFC, however it is transport agnostic.

NDEF defines messages and records. An NDEF Record contains typed data, such as MIME-type media, a URI, or a custom application payload. An NDEF Message is a container for one or more NDEF Records.

When an Android device receives an NDEF Message (for example by reading an NFC tag) it processes it through a dispatch mechanism to determine an activity to launch. The type of the first record in the message has special importance for message dispatch, so design this record carefully.

Use NdefMessage(byte[]) to construct an NDEF Message from binary data, or NdefMessage(NdefRecord[]) to construct from one or more NdefRecords.

NdefMessage and NdefRecord implementations are always available, even on Android devices that do not have NFC hardware.

NdefRecords are intended to be immutable (and thread-safe), however they may contain mutable fields. So take care not to modify mutable fields passed into constructors, or modify mutable fields obtained by getter methods, unless such modification is explicitly marked as safe.

See also:

Summary

Inherited constants

From interface android.os.Parcelable

Fields

public static final Creator<NdefMessage> CREATOR

Public constructors

NdefMessage(byte[] data)

Construct an NDEF Message by parsing raw bytes.

NdefMessage(NdefRecord record, NdefRecord... records)

Construct an NDEF Message from one or more NDEF Records.

NdefMessage(NdefRecord[] records)

Construct an NDEF Message from one or more NDEF Records.

Public methods

int describeContents()

Describe the kinds of special objects contained in this Parcelable instance's marshaled representation.

boolean equals(Object obj)

Returns true if the specified NDEF Message contains identical NDEF Records.

int getByteArrayLength()

Return the length of this NDEF Message if it is written to a byte array with toByteArray().

NdefRecord[] getRecords()

Get the NDEF Records inside this NDEF Message.

int hashCode()

Returns a hash code value for the object.

byte[] toByteArray()

Return this NDEF Message as raw bytes.

String toString()

Returns a string representation of the object.

void writeToParcel(Parcel dest, int flags)

Flatten this object in to a Parcel.

Inherited methods

From class java.lang.Object
From interface android.os.Parcelable

Fields

CREATOR

Added in API level 9
Creator<NdefMessage> CREATOR

Public constructors

NdefMessage

Added in API level 9
NdefMessage (byte[] data)

Construct an NDEF Message by parsing raw bytes.

Strict validation of the NDEF binary structure is performed: there must be at least one record, every record flag must be correct, and the total length of the message must match the length of the input data.

This parser can handle chunked records, and converts them into logical NdefRecords within the message.

Once the input data has been parsed to one or more logical records, basic validation of the tnf, type, id, and payload fields of each record is performed, as per the documentation on on NdefRecord(short, byte[], byte[], byte[])

If either strict validation of the binary format fails, or basic validation during record construction fails, a FormatException is thrown

Deep inspection of the type, id and payload fields of each record is not performed, so it is possible to parse input that has a valid binary format and confirms to the basic validation requirements of NdefRecord(short, byte[], byte[], byte[]), but fails more strict requirements as specified by the NFC Forum.

It is safe to re-use the data byte array after construction: this constructor will make an internal copy of all necessary fields.

Parameters
data byte: raw bytes to parse
Throws
FormatException if the data cannot be parsed

NdefMessage

Added in API level 16
NdefMessage (NdefRecord record, 
                NdefRecord... records)

Construct an NDEF Message from one or more NDEF Records.

Parameters
record NdefRecord: first record (mandatory)
records NdefRecord: additional records (optional)

NdefMessage

Added in API level 9
NdefMessage (NdefRecord[] records)

Construct an NDEF Message from one or more NDEF Records.

Parameters
records NdefRecord: one or more records

Public methods

describeContents

Added in API level 9
int describeContents ()

Describe the kinds of special objects contained in this Parcelable instance's marshaled representation. For example, if the object will include a file descriptor in the output of writeToParcel(Parcel, int), the return value of this method must include the CONTENTS_FILE_DESCRIPTOR bit.

Returns
int a bitmask indicating the set of special object types marshaled by this Parcelable object instance.

equals

Added in API level 9
boolean equals (Object obj)

Returns true if the specified NDEF Message contains identical NDEF Records.

Parameters
obj Object: the reference object with which to compare.
Returns
boolean true if this object is the same as the obj argument; false otherwise.

getByteArrayLength

Added in API level 16
int getByteArrayLength ()

Return the length of this NDEF Message if it is written to a byte array with toByteArray().

An NDEF Message can be formatted to bytes in different ways depending on chunking, SR, and ID flags, so the length returned by this method may not be equal to the length of the original byte array used to construct this NDEF Message. However it will always be equal to the length of the byte array produced by toByteArray().

Returns
int length of this NDEF Message when written to bytes with toByteArray()

See also:

getRecords

Added in API level 9
NdefRecord[] getRecords ()

Get the NDEF Records inside this NDEF Message.

An NdefMessage always has one or more NDEF Records: so the following code to retrieve the first record is always safe (no need to check for null or array length >= 1):

 NdefRecord firstRecord = ndefMessage.getRecords()[0];
 

Returns
NdefRecord[] array of one or more NDEF records.

hashCode

Added in API level 9
int hashCode ()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Returns
int a hash code value for this object.

toByteArray

Added in API level 9
byte[] toByteArray ()

Return this NDEF Message as raw bytes.

The NDEF Message is formatted as per the NDEF 1.0 specification, and the byte array is suitable for network transmission or storage in an NFC Forum NDEF compatible tag.

This method will not chunk any records, and will always use the short record (SR) format and omit the identifier field when possible.

Returns
byte[] NDEF Message in binary format

See also:

toString

Added in API level 9
String toString ()

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Returns
String a string representation of the object.

writeToParcel

Added in API level 9
void writeToParcel (Parcel dest, 
                int flags)

Flatten this object in to a Parcel.

Parameters
dest Parcel: The Parcel in which the object should be written.
flags int: Additional flags about how the object should be written. May be 0 or PARCELABLE_WRITE_RETURN_VALUE.
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