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franckbour / Plugin.NFC

A Cross-Platform NFC (Near Field Communication) plugin to easily read and write NFC tags in your application.
MIT License
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The "Identifier" Property in the ITagInfo Object is Reversed for iOS #62

Closed jervaughan closed 3 years ago

jervaughan commented 3 years ago

Description

When scanning an NFC tag, the "Identifier" property in the ITagInfo object is reversed for iOS, and subsequently shows a different SerialNumber property for the same tag.

The "NFC Tools" app on both Android and iOS show the same serial number when scanning a tag. Android using Plugin.NFC also matches this serial number. It's only when I use Plugin.NFC on iOS that I'm seeing the reversal.

Steps to Reproduce

  1. Set a breakpoint on the "Current_OnMessageReceived" method.
  2. Use "Quick Watch" in Visual Studio to analyze the ITagInfo parameter object.
  3. Compare values between iOS and Android.

Expected Behavior

I expect to receive the same serial number on iOS and Android when scanning a tag. I use the serial number for a database lookup request, so they need to be the same across platforms.

Basic Information

Screenshots

Android image

iOS image

saamerm commented 3 years ago

@JerVaughan any recommendations on what can be changed in order to fix this?

jervaughan commented 3 years ago

@JerVaughan any recommendations on what can be changed in order to fix this?

For now, I've modified my "Current_OnMessageReceived" method in my app with the following when getting the tag's serial number... I'm just reversing the array if it's iOS. I've successfully modified your code earlier to add-in the pending fix for reading ISO15693 tags (Issue #41 and Issue #61) until it's released, so I'm fairly comfortable with it. The "GetTagIdentifier(INFCNdefTag tag)" method in NFC.iOS.cs probably needs to be changed to reverse the byte array before returning the identifier, but I only have ISO15693 tags to test with.

byte[] identifier = tagInfo.Identifier; string serialNumber = Device.RuntimePlatform == Device.iOS ? NFCUtils.ByteArrayToHexString(identifier.Reverse().ToArray()) : NFCUtils.ByteArrayToHexString(identifier);

saamerm commented 3 years ago

@JerVaughan Thanks for that, it is very strange. Is there any documentation that shows that iOS reverses the byte array? I certainly don't think anything in our code causes the reverse isn't it?

franckbour commented 3 years ago

The tag identifier seems to be reversed only with ISO15693 tags but unfortunately, I have none of these. I cannot confirm that assertion for the moment.

f-richter commented 3 years ago

I can confirm that assertion. Sorry for non-english language in the screenshots. So you can see that the serial number (Seriennummer) in iOS read with the Plugin.NFC is reversed. @JerVaughan maybe you can create a pull request?

NFC Tools Android NFC Tools iOS Plugin NFC Android Plugin NFC iOS
saamerm commented 3 years ago

This seems to be an iOS bug because I haven't seen this assertion anywhere in their documentation. Have you guys seen anything that got you to try to do the reverse in the first place?

franckbour commented 3 years ago

No, I didn't know that.