Allow iOS to read tag before writing

README.md

@@ -307,12 +307,74 @@ Function `nfc.write` writes an NdefMessage to a NFC tag.
 
 On **Android** this method *must* be called from within an NDEF Event Handler.
 
-On **iOS** this method should be called outside the NDEF Event Handler, it will start a new scanning session. 
+On **iOS** this method can be called outside the NDEF Event Handler, it will start a new scanning session. Optionally you can reuse the read session to write data. See example below.
 
 On **Windows** this method *may* be called from within the NDEF Event Handler.
 
 On **Windows Phone 8.1** this method should be called outside the NDEF Event Handler, otherwise Windows tries to read the tag contents as you are writing to the tag.
 
+### Examples
+
+#### Android
+
+On Android, write must be called inside an event handler
+
+    function onNfc(nfcEvent) {
+
+        console.log(nfcEvent.tag);
+        
+        var message = [
+            ndef.textRecord(new String(new Date()))
+        ];
+        
+        nfc.write(
+            message,
+            success => console.log('wrote data to tag'),
+            error => console.log(error)
+        );
+
+    nfc.addNdefListener(onNfc);
+
+
+#### iOS - Simple
+
+Calling `nfc.write` on iOS will create a new session and write data when the user taps a NFC tag
+
+        var message = [
+            ndef.textRecord("Hello, world")
+        ];
+
+        nfc.write(
+            message,
+            success => console.log('wrote data to tag'),
+            error => console.log(error)
+        );
+
+#### iOS - Read and Write
+
+On iOS you can optionally write to NFC tag using the read session
+
+        try {
+            let tag = await nfc.scanNdef({ keepSessionOpen: true});
+
+            // you can read tag data here
+            console.log(tag);
+            
+            // this example writes a new message with a timestamp
+            var message = [
+                ndef.textRecord(new String(new Date()))
+            ];
+
+            nfc.write(
+                message,
+                success => console.log('wrote data to tag'),
+                error => console.log(error)
+            );
+
+        } catch (err) {
+            console.log(err);
+        }
+
 ### Supported Platforms
 
 - Android

src/ios/NfcPlugin.m

@@ -9,12 +9,15 @@
 @interface NfcPlugin() {
     NSString* sessionCallbackId;
     NSString* channelCallbackId;
+    id<NFCNDEFTag> connectedTag API_AVAILABLE(ios(13.0));
+    NFCNDEFStatus connectedTagStatus API_AVAILABLE(ios(13.0));
 }
 @property (nonatomic, assign) BOOL writeMode;
 @property (nonatomic, assign) BOOL shouldUseTagReaderSession;
 @property (nonatomic, assign) BOOL sendCallbackOnSessionStart;
 @property (nonatomic, assign) BOOL returnTagInCallback;
 @property (nonatomic, assign) BOOL returnTagInEvent;
+@property (nonatomic, assign) BOOL keepSessionOpen;
 @property (strong, nonatomic) NFCReaderSession *nfcSession API_AVAILABLE(ios(11.0));
 @property (strong, nonatomic) NFCNDEFMessage *messageToWrite API_AVAILABLE(ios(11.0));
 @end
@@ -52,7 +55,8 @@ - (void)beginSession:(CDVInvokedUrlCommand*)command {
     self.sendCallbackOnSessionStart = YES;  // Not sure why we were doing this
     self.returnTagInCallback = NO;
     self.returnTagInEvent = YES;
-
+    self.keepSessionOpen = NO;
+
     [self startScanSession:command];
 }
 
@@ -64,6 +68,9 @@ - (void)scanNdef:(CDVInvokedUrlCommand*)command {
     self.returnTagInCallback = YES;
     self.returnTagInEvent = NO;
 
+    NSArray<NSDictionary *> *options = [command argumentAtIndex:0];
+    self.keepSessionOpen = [options valueForKey:@"keepSessionOpen"];
+
     [self startScanSession:command];
 }
 
@@ -75,6 +82,9 @@ - (void)scanTag:(CDVInvokedUrlCommand*)command {
     self.returnTagInCallback = YES;
     self.returnTagInEvent = NO;
 
+    NSArray<NSDictionary *> *options = [command argumentAtIndex:0];
+    self.keepSessionOpen = [options valueForKey:@"keepSessionOpen"];
+
     [self startScanSession:command];
 }
 
@@ -83,6 +93,7 @@ - (void)writeTag:(CDVInvokedUrlCommand*)command API_AVAILABLE(ios(13.0)){
 
     self.writeMode = YES;
     self.shouldUseTagReaderSession = NO;
+    BOOL reusingSession = NO;
 
     NSArray<NSDictionary *> *ndefData = [command argumentAtIndex:0];
 
@@ -107,30 +118,41 @@ - (void)writeTag:(CDVInvokedUrlCommand*)command API_AVAILABLE(ios(13.0)){
         [self.commandDelegate sendPluginResult:pluginResult callbackId:command.callbackId];
         return;
     }
-
-    // Start the NFC Session
-    if (self.shouldUseTagReaderSession) {
-        NSLog(@"Using NFCTagReaderSession");
 
-        self.nfcSession = [[NFCTagReaderSession new]
-                   initWithPollingOption:(NFCPollingISO14443 | NFCPollingISO15693)
-                   delegate:self queue:dispatch_get_main_queue()];
+    if (self.nfcSession && self.nfcSession.isReady) {       // reuse existing session
+        reusingSession = YES;
+    } else {                                                // create a new session
+        if (self.shouldUseTagReaderSession) {
+            NSLog(@"Using NFCTagReaderSession");
 
-    } else {
-        NSLog(@"Using NFCTagReaderSession");
-        self.nfcSession = [[NFCNDEFReaderSession new]initWithDelegate:self queue:nil invalidateAfterFirstRead:FALSE];
+            self.nfcSession = [[NFCTagReaderSession new]
+                       initWithPollingOption:(NFCPollingISO14443 | NFCPollingISO15693)
+                       delegate:self queue:dispatch_get_main_queue()];
+
+        } else {
+            NSLog(@"Using NFCTagReaderSession");
+            self.nfcSession = [[NFCNDEFReaderSession new]initWithDelegate:self queue:nil invalidateAfterFirstRead:FALSE];
+        }
     }
 
     self.nfcSession.alertMessage = @"Hold near writable NFC tag to update.";
     sessionCallbackId = [command.callbackId copy];
-    [self.nfcSession beginSession];
+
+    if (reusingSession) {                   // reusing a read session to write
+        self.keepSessionOpen = NO;          // close session after writing
+        [self writeNDEFTag:self.nfcSession status:connectedTagStatus tag:connectedTag];
+    } else {
+        [self.nfcSession beginSession];
+    }
 }
 
 - (void)cancelScan:(CDVInvokedUrlCommand*)command API_AVAILABLE(ios(11.0)){
     NSLog(@"cancelScan");
     if (self.nfcSession) {
         [self.nfcSession invalidateSession];
     }
+    connectedTag = NULL;
+    connectedTagStatus = NFCNDEFStatusNotSupported;
     CDVPluginResult *pluginResult = [CDVPluginResult resultWithStatus:CDVCommandStatus_OK];
     [self.commandDelegate sendPluginResult:pluginResult callbackId:command.callbackId];
 }
@@ -326,6 +348,11 @@ - (void)processNDEFTag: (NFCReaderSession *)session tag:(__kindof id<NFCNDEFTag>
         if (self.writeMode) {
             [self writeNDEFTag:session status:status tag:tag];
         } else {
+            // save tag & status so we can re-use in write
+            if (self.keepSessionOpen) {
+                self->connectedTagStatus = status;
+                self->connectedTag = tag;
+            }
             [self readNDEFTag:session status:status tag:tag metaData:metaData];
         }
 
@@ -456,8 +483,16 @@ - (void) sessionDidBecomeActive:(NFCReaderSession *) session  API_AVAILABLE(ios(
 }
 
 - (void) closeSession:(NFCReaderSession *) session  API_AVAILABLE(ios(11.0)){
+
+    // this is a hack to keep a read session open to allow writing
+    if (self.keepSessionOpen) {
+        return;
+    }
+
     // kill the callback so the Cordova doesn't get "Session invalidated by user"
     sessionCallbackId = NULL;
+    connectedTag = NULL;
+    connectedTagStatus = NFCNDEFStatusNotSupported;
     [session invalidateSession];
 }
 
@@ -466,6 +501,8 @@ - (void) closeSession:(NFCReaderSession *) session withError:(NSString *) errorM
 
     // kill the callback so Cordova doesn't get "Session invalidated by user"
     sessionCallbackId = NULL;
+    connectedTag = NULL;
+    connectedTagStatus = NFCNDEFStatusNotSupported;
 
     if (@available(iOS 13.0, *)) {
         [session invalidateSessionWithErrorMessage:errorMessage];

www/phonegap-nfc.js

@@ -501,16 +501,16 @@ var nfc = {
     },
 
     // iOS only - scan for NFC NDEF tag using NFCNDEFReaderSession
-    scanNdef: function () {
+    scanNdef: function (options) {
         return new Promise(function(resolve, reject) {
-            cordova.exec(resolve, reject, "NfcPlugin", "scanNdef", []);
+            cordova.exec(resolve, reject, "NfcPlugin", "scanNdef", [options]);
         });
     },
 
     // iOS only - scan for NFC Tag using NFCTagReaderSession
     scanTag: function (options) {
         return new Promise(function(resolve, reject) {
-            cordova.exec(resolve, reject, "NfcPlugin", "scanTag", []);
+            cordova.exec(resolve, reject, "NfcPlugin", "scanTag", [options]);
         });
     },