refactor: centralize Android NFC method exception handling

[knthm]

Reduces code duplication and improves readability.

Fixes #168

[Harry-Chen]

Thanks! I am actually thinking about some more elegant ways to handle all possible exceptions. Something like:

fun handleException(ex: Exception, result: Result?, desc: String) {
    Log.e(TAG, "$desc error", ex)
    val excMessage = ex.localizedMessage
    when (ex) {
        is IOException -> result?.error("500", "Communication error", excMessage )
        is SecurityException -> result?.error("503", "Tag already removed", excMessage)
        // some more types
        else -> result?.error("510", "Unhandled error", excMessage) // I choose this code just randomly.
    }
}

Then it could be called from all catch blocks. What's your opinion on this?

[knthm]

With the current amount of catch blocks per operation I was thinking along the same lines, but thought it safer at first to maintain the same pattern.

I suppose refactoring the exception handling wouldn't take too much time and would definitely make things a lot cleaner.

My main concern is I can't physically test the other tag types to ensure the behavior triggering the exception doesn't differ slightly.

[Harry-Chen]

My main concern is I can't physically test the other tag types to ensure the behavior triggering the exception doesn't differ slightly.

AFAIK Android NFC APIs mainly throw:

• IOException and SecurityException in every IO-related API
• IllegalArgumentException in transceive
• FormatException in NDEF-related APIs

There are additional InvocationTargetException and NoSuchMethodException because reflection is used to simplify transceive.

Seems it's safe to refactor, since no two different APIs throws the same exceptions except IOException and SecurityException.

[knthm]

Good points, I went ahead and offloaded it into more or less the copy-pasted version of your suggestion :)

[Harry-Chen]

Yeah! This looks much better now. I just found that it could be merged into runOnNfcThread, like:

private fun runOnNfcThread(result: Result, desc: String, fn: () -> Unit) {
    val wrappedFn = Runnable {
        try {
            fn()
        } catch (ex: Exception) {
            handleException(ex, result, desc)
        }
    }
    if (!nfcHandler.post(fn)) {
        result.error("500", "Failed to post job to NFC Handler thread.", null)
    }
}

Then:

• result could be non-null.
• the catch here could be absorbed:

  flutter_nfc_kit/android/src/main/kotlin/im/nfc/flutter_nfc_kit/FlutterNfcKitPlugin.kt

  Lines 595 to 600 in 27fe9ba

  	try {
  	nfcAdapter.enableReaderMode(activity.get(), pollHandler, technologies, null)
  	} catch (ex: Exception) {
  	Log.e(TAG, "Cannot enable reader mode", ex)
  	result.error("500", "Cannot enable reader mode", ex.localizedMessage)
  	}

By the way, there is an extra space at:

flutter_nfc_kit/android/src/main/kotlin/im/nfc/flutter_nfc_kit/FlutterNfcKitPlugin.kt

Line 70 in 27fe9ba

is IOException -> result?.error("500", "Communication error", excMessage )

Will you please make the changes, and I'm really happy to merge.

[knthm]

I just found that it could be merged into runOnNfcThread

Oh! That's a lot better, agreed.

I ended up moving handleException into runOnNfcThread, since their usage is mutually inclusive, IMHO.

Resolved the other two mentions as well.