class QNdefFilter#

The QNdefFilter class provides a filter for matching NDEF messages. More…

Synopsis#

Methods#

def __init__()
def appendRecord()
def clear()
def match()
def orderMatch()
def recordAt()
def recordCount()
def setOrderMatch()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

The QNdefFilter encapsulates the structure of an NDEF message and is used for matching messages that have a particular structure.

The following filter matches NDEF messages that contain a single smart poster record:

QNdefFilter filter;
filter.append(QNdefRecord::NfcRtd, "Sp");

The following filter matches NDEF messages that contain a URI, a localized piece of text and an optional JPEG image. The order of the records must be in the order specified:

QNdefFilter filter;
filter.setOrderMatch(true);
filter.appendRecord(QNdefRecord::NfcRtd, "U");
filter.appendRecord<QNdefNfcTextRecord>();
filter.appendRecord(QNdefRecord::Mime, "image/jpeg", 0, 1);

The match() method can be used to check if a message matches the filter.

Matching Algorithms#

The filter behavior depends on the value of orderMatch() parameter.

Note

In the discussion below we will consider the filter records to be equal if their typeNameFormat and type parameters match. Joining two records means adding their minimum and maximum values, respectively.

Unordered Matching#

If the record order is not taken into account, all the equal records in the filter can be joined. The resulting filter will contain only unique records, each with the updated minimum and maximum value.

Consider the following example:

QNdefFilter filter;
filter.appendRecord<QNdefNfcTextRecord>(0, 1);
filter.appendRecord<QNdefNfcTextRecord>(0, 1);
filter.appendRecord(QNdefRecord::Mime, "", 1, 1);
filter.appendRecord<QNdefNfcTextRecord>(1, 1);
filter.setOrderMatch(false);

With the unordered matching, the filter will be simplified to the following:

QNdefFilter filter;
filter.appendRecord<QNdefNfcTextRecord>(1, 3);
filter.appendRecord(QNdefRecord::Mime, "", 1, 1);
filter.setOrderMatch(false);

Once the filter contains only the unique records, the matching algorithm iterates through the message and calculates the actual amount of records of each type. If all the actual amounts fit in the corresponding [minimum, maximum] ranges, the matching algorithm returns true.

Ordered Matching#

If the record order is important, a different approach is applied. In this case the equal records can’t be simply joined together. However, the consecutive equal records can still be joined. Then, the matching algorithm iterates through the message, this time also taking the positions of the records into account.

Handling Empty Type in Filter Record#

It’s possible to add a filter record with an empty type. In this case the empty type will act as a wildcard for any type.

For example, the filter can be defined as follows:

QNdefFilter filter;
filter.addRecord(QNdefRecord::Mime, "", 1, 1);

This filter specifies that the message must contain exactly one NDEF record with Mime typeNameFormat (), and any type ().

Handling Extra Records in the Message#

If the message contains some records that do not match any record in the filter, the matching algorithm will return false.

Filter Examples#

In the table below, each filter record is specified by the following parameters (in the given order):

typeNameFormat - contains the typeNameFormat () of the record.

type - contains the type () of the record.

minimum - contains the minimum amount of occurrences of the record in the message.

maximum - contains the maximum amount of occurrences of the record in the message.

The filter contains multiple records.

The message consists of multiple QNdefRecord s. In the table below, only the typeNameFormat () and type () of each record will be shown, because the other parameters do not matter for filtering.

Filter

Message

Match Result

Comment

Empty filter

Empty message

Match

Empty filter

Non-empty message

No match

Non-empty filter

Empty message

No match

[( NfcRtd , “T”, 1, 2), ( Mime , “”, 1, 1), ( Empty , “”, 0, 100)]

[( Mime , “image/jpeg”), ( Empty , “”), ( NfcRtd , “T”), ( Empty , “”), ( NfcRtd , “T”)]

Unordered: match

Ordered filter does not match because the message must start with a NfcRtd record, but it starts with Mime .

Ordered: no match

[( NfcRtd , “T”, 0, 2), ( Mime , “”, 1, 1), ( NfcRtd , “T”, 1, 1)]

[( NfcRtd , “T”), ( NfcRtd , “T”), ( Mime , “image/jpeg”)]

Unordered: match

Ordered filter does not match because an NfcRtd record is expected after Mime , but the message does not have it.

Ordered: no match

[( NfcRtd , “T”, 0, 2), ( NfcRtd , “T”, 1, 1), ( Mime , “”, 1, 1)]

[( NfcRtd , “T”), ( Mime , “image/jpeg”)]

Unordered: match

Both cases match because the message contains the required minimum of records in the correct order.

Ordered: match

Filter	Message	Match Result	Comment
Empty filter	Empty message	Match
Empty filter	Non-empty message	No match
Non-empty filter	Empty message	No match
[( `NfcRtd` , “T”, 1, 2), ( `Mime` , “”, 1, 1), ( `Empty` , “”, 0, 100)]	[( `Mime` , “image/jpeg”), ( `Empty` , “”), ( `NfcRtd` , “T”), ( `Empty` , “”), ( `NfcRtd` , “T”)]	Unordered: match	Ordered filter does not match because the message must start with a `NfcRtd` record, but it starts with `Mime` .
Ordered: no match
[( `NfcRtd` , “T”, 0, 2), ( `Mime` , “”, 1, 1), ( `NfcRtd` , “T”, 1, 1)]	[( `NfcRtd` , “T”), ( `NfcRtd` , “T”), ( `Mime` , “image/jpeg”)]	Unordered: match	Ordered filter does not match because an `NfcRtd` record is expected after `Mime` , but the message does not have it.
Ordered: no match
[( `NfcRtd` , “T”, 0, 2), ( `NfcRtd` , “T”, 1, 1), ( `Mime` , “”, 1, 1)]	[( `NfcRtd` , “T”), ( `Mime` , “image/jpeg”)]	Unordered: match	Both cases match because the message contains the required minimum of records in the correct order.
Ordered: match

__init__()#

Constructs a new NDEF filter.

__init__(other)

Parameters:: other – QNdefFilter

Constructs a new NDEF filter that is a copy of other.

appendRecord(typeNameFormat, type[, min=1[, max=1]])#

Parameters:

typeNameFormat – TypeNameFormat
type – QByteArray
min – int
max – int

Return type:

bool

Appends a record with type name format typeNameFormat and type type to the NDEF filter. The record must occur between min and max times in the NDEF message.

Returns true if the record was appended successfully. Otherwise returns false.

appendRecord(record)

Parameters:: record – Record
Return type:: bool

Verifies the record and appends it to the NDEF filter.

Returns true if the record was appended successfully. Otherwise returns false.

clear()#

Clears the filter.

match(message)#

Parameters:: message – QNdefMessage
Return type:: bool

Returns true if the message matches the given filter. Otherwise returns false.

See Matching Algorithms for more detailed explanation of matching.

orderMatch()#

Return type:: bool

Returns true if the filter takes NDEF record order into account when matching. Otherwise returns false.

See also

setOrderMatch()

recordAt(i)#

Parameters:: i – int
Return type:: Record

Returns the NDEF record at index i.

i must be a valid index (i.e. 0 <= i < recordCount() ).

See also

recordCount()

recordCount()#

Return type:: int

Returns the number of NDEF records in the filter.

setOrderMatch(on)#

Parameters:: on – bool

Sets the ordering requirements of the filter. If on is true, the filter will only match if the order of records in the filter matches the order of the records in the NDEF message. If on is false, the order of the records is not taken into account when matching.

By default record order is not taken into account.

See also

orderMatch()