I hate to seem like a nag on this topic, but I've got some more
concerns about the documentation, and your answer. Let's consider an
example as described in the reference page for NfcAdapter, which seems
to be more correct than the DevGuide for NFC:
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
<!-- capture anything using NfcF -->
<tech-list>
<tech>android.nfc.tech.NfcF</tech>
</tech-list>
<!-- OR -->
<!-- capture all MIFARE Classics with NDEF payloads -->
<tech-list>
<tech>android.nfc.tech.NfcA</tech>
<tech>android.nfc.tech.MifareClassic</tech>
<tech>android.nfc.tech.Ndef</tech>
</tech-list>
</resources>
If I have a tag that enumerates NfcA and MifareClassic but does not
enumerate Ndef, I'm assuming that this activity would not receive that
NFC tech intent. Correct? None of the intent-filter's tech-list sets
is a subset of
Tag.getTechList().
If I have a tag that enumerates NfcF and Ndef, I'm assuming that this
activity *would* receive that NFC tech intent, right? The intent-
filter tech-list of NfcF *is* a sub-set of Tag.getTechList(). Correct?
And this jives with your earlier answer about not having to specify
both MifareUltralight *and* NfcA in a tech-list since if the tech-list
has both and my tech-list only has one, it's still a sub-set so it
will match. It could actually be dangerous to specify both in case
some tag doesn't enumerate NfcA, then the tech-list would not be a sub-
set of the Tag's tech list so there'd be no match.
Just one more thing about the <category> tag with the intent filters
for NFC tags. In the NFCDemo, for the intent-filter for TAG_DISCOVERED
there is a <category> tag within the <intent-filter>, as one would
expect in order to receive an intent that carries no data. This
<category> tag is not present in the NfcAdapter reference page or the
NFC DevGuide page, but I think it should be. Correct?
What I can't tell is whether or not the <category> tag is required
within the <intent-filter> when the action is TECH_DISCOVERED. I
haven't been able to figure out the bytes to generate a fake non-Ndef
tag to send from FakeTagsActivity. And when I save my manifest.xml
file either way, I get no errors.
I appreciate any help that I can get. Thanks!
- dave
On Feb 23, 1:01 pm, Nick Pelly <[email protected]> wrote:
> On Wed, Feb 23, 2011 at 8:45 AM, davemac <[email protected]> wrote:
> > What you're saying doesn't jive with the documentation, which says the
> > following (onhttp://developer.android.com/guide/topics/nfc/index.html):
>
> > Specifiying [sic] multiple technologies within the same list tells the
> > system to filter tags that support all of the technologies.
>
> This particular sentence is a little confusing in the docs, i'll try and
> have it improved.
>
> > The
> > example below never filters a tag because no tag supports all of the
> > technologies at once. You can remove the ones that you do not need.
> > The docs say a tag will only match if all tag technologies are listed
> > in my tech-list,
>
> No the docs don't say that.
>
> There is a better explanation here, which matches with how I explained it,
> which is how it is :)
>
> http://developer.android.com/reference/android/nfc/NfcAdapter.html#AC...
>
> """
> A tag matches if any of the tech-list sets is a subset of
> Tag.getTechList()<http://developer.android.com/reference/android/nfc/Tag.html#getTechList()>.
> Each of the tech-lists is considered independently and the activity is
> considered a match is any single tech-list matches the tag that was
> discovered. This provides AND and OR semantics for filtering desired techs.
> """
>
> and all tech-list technologies are implemented by the
>
> > tag. You're saying that the tag's technologies only need to match a
> > sub-set of the tech-list.
>
> yes
>
> > Or are you saying that a MifareUltralight
> > tag only reports MifareUltralight technology?
>
> No.
>
> > Or that the docs are
> > wrong?
>
> No they're just a little confusing.
>
> > I have a related question that I hope you don't mind answering here as
> > well. To build an intent filter in code that supports tech, how do you
> > specify the techlists on it? Or does this only work in foreground
> > dispatch mode?
>
> I am a little hazy on the details for this one, but I believe the best
> practice is to define all the intent filters you might want in the manifest,
> and then turn intent-filters on and off at run-time.
>
> > - dave
>
> > On Feb 23, 12:41 am, Nick Pelly <[email protected]> wrote:
> > > On Tue, Feb 22, 2011 at 6:50 PM, davemac <[email protected]> wrote:
> > > > I'm reading the documentation on NFC tags and intent filters to match
> > > > on. For an action of ACTION_TECH_DISCOVERED, the intent filter must
> > > > list the technologies to match on, using a filter file. What I wanted
> > > > clarification on is whether or not I need to also specify for example
> > > > NfcA when I'm looking for a Mifare Utralight tag.
>
> > > > For the Mifare Ultralight tag, the documentation says this:
> > > > NfcA will also be enumerated on the tag, because all MIFARE Ultralight
> > > > tags are also NfcA tags.
>
> > > > This suggests to me that my XML filter file should say this:
>
> > > > <resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
> > > > <tech-list>
> > > > <tech>android.nfc.tech.NfcA</tech>
> > > > <tech>android.nfc.tech.MifareUltralight</tech>
> > > > </tech-list>
> > > > </resources>
>
> > > > because if the tag is enumerating NfcA in addition to
> > > > MifareUltralight, my intent filter will only match if I specify both
> > > > technologies, not just MifareUltralight. Is that true? This applies to
> > > > IsoDep as well, which enumerates both NfcA and NfcB, in which case I
> > > > would need to specify all three. True? I don't have available hardware
> > > > to test this for myself. Thanks for your help.
>
> > > You do not need to specify both NfcA and MifareUltralight. You can just
> > > specify MifareUltralight. The <tech-list> only requires a subset of
> > tech's
> > > in order to match.
>
> > > In the case of MIFARE Ultralight, it happens to always be based on NfcA
> > > technology. So tags with the MifareUltralight tech will always also have
> > the
> > > NfcA tech. So there is no harm also putting NfcA in the <tech-list>. But
> > it
> > > is not strictly required.
>
> > > Nick
>
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