# Android NFC Library

|Home | Reading NFC Tags | Writing NFC Tags | Creating NdefMessages | Exception Handling 
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|[How it works](Home)|**Reading**|[Writing](WriteUtility)|[NdefMessages](NdefMessage) |[Exceptions](ExceptionHandling)
## ***Read Utility***

For reading an NFC tag we have added some convenience methods.

When you extend the `NFCTechDiscoveredActivity`  : 

``` Java
	public void onNewIntent(Intent paramIntent) {
		super.onNewIntent(paramIntent);
		for (String data : getNfcMessages()) {
    	    Toast.makeText(this, data + "", Toast.LENGTH_SHORT).show();
    	}
	}
```

If you do not, then the following snippets provide you with the ability to read the tag.

``` java
	public void onNewIntent(Intent paramIntent) {
		super.onNewIntent(paramIntent);
		for (String data : mNfcReadUtility.readFromTagWithMap(paramIntent).values())
		{
			Toast.makeText(this,data,Toast.LENGTH_SHORT).show();
		}
	}
```
``` Java
	public void onNewIntent(Intent paramIntent) {
		super.onNewIntent(paramIntent);
		SparseArray<String> messages = mNfcReadUtility.readFromTagWithSparseArray(paramIntent);
  		for (int i = 0; i < messages.size() ; i++ )
 	    {
 	    	Toast.makeText(this,messages.valueAt(i),Toast.LENGTH_SHORT).show();
    	}
```
Somewhere you will probably ***define a field*** 
`NfcReadUtility mNfcReadUtility = new NfcReadUtilityImpl();`



As you'll see, you can use either a map or a [SparseArray]. The [SparseArray] allows us to avoid a lot of the overhead Map produces due to the unboxing and relying on an actual Object for each key entry, it still maintains a feature to index the records on type.

### *When filtering on the Nfc Payload Type*

As the NfcType is used as an index in the [SparseArray], you can just execute the following line of code in order to get the messages of the type you're interested in :

```
 String website  = mNfcReadUtility.readFromTag(paramIntent).get(NfcPayloadHeader.HTTP);
```
This will return either null when there is no such record, or the actual record in the tag.
All of the currently known payload headers are recorded in the class `NfcPayloadHeader`, so use them to your advantage !



### *When you actually don't care about the Nfc Payload Type*

With this in mind, it might come in handy to have a method like this defined somewhere, in case you do not care about the NFC type : 

``` Java
    private List<String> transformSparseArrayToArrayList(SparseArray<String> sparseArray) {
        List<String> list = new ArrayList<String>(sparseArray.size());
        for (int i = 0; i < sparseArray.size(); i++) {
            list.add(sparseArray.valueAt(i));
        }
        return list;
    }
```
This transforms the [SparseArray]<String> returned by our method into a List<String>.
This is the exact same method used internally by the `getNfcMessages()` method.


****
***Note*** : It is not possible to use a for-each to loop through a [SparseArray], keep this in mind, you'll have to use a normal for-loop to achieve this.

****
Should you encounter a discrepancy between the standards from the [NFC Forum] and our implementation, be sure to inform us!

[SparseArray]:http://developer.android.com/reference/android/util/SparseArray.html

[NFC Forum]:http://members.nfc-forum.org/specs/