We Keep Coding

Zebra RFID API Read Access Operation Code return null

I'm trying to develop a small Application for a Zebra handheld rfid reader and can't find a way to access the MemoryBank of the tag. My reader configuration is as follows:
private void ConfigureReader() {
if (reader.isConnected()) {
TriggerInfo triggerInfo = new TriggerInfo();
triggerInfo.StartTrigger.setTriggerType(START_TRIGGER_TYPE.START_TRIGGER_TYPE_IMMEDIATE);
triggerInfo.StopTrigger.setTriggerType(STOP_TRIGGER_TYPE.STOP_TRIGGER_TYPE_IMMEDIATE);
try {
// receive events from reader
if (eventHandler == null){
eventHandler = new EventHandler();
}
reader.Events.addEventsListener(eventHandler);
// HH event
reader.Events.setHandheldEvent(true);
// tag event with tag data
reader.Events.setTagReadEvent(true);
reader.Events.setAttachTagDataWithReadEvent(true);
// set trigger mode as rfid so scanner beam will not come
reader.Config.setTriggerMode(ENUM_TRIGGER_MODE.RFID_MODE, true);
// set start and stop triggers
reader.Config.setStartTrigger(triggerInfo.StartTrigger);
reader.Config.setStopTrigger(triggerInfo.StopTrigger);
} catch (InvalidUsageException e) {
e.printStackTrace();
} catch (OperationFailureException e) {
e.printStackTrace();
}
}
}
And the eventReadNotify looks like this:
public void eventReadNotify(RfidReadEvents e) {
// Recommended to use new method getReadTagsEx for better performance in case of large tag population
TagData[] myTags = reader.Actions.getReadTags(100);
if (myTags != null) {
for (int index = 0; index < myTags.length; index++) {
Log.d(TAG, "Tag ID " + myTags[index].getTagID());
ACCESS_OPERATION_CODE aoc = myTags[index].getOpCode();
ACCESS_OPERATION_STATUS aos = myTags[index].getOpStatus();
if (aoc == ACCESS_OPERATION_CODE.ACCESS_OPERATION_READ && aos == ACCESS_OPERATION_STATUS.ACCESS_SUCCESS) {
if (myTags[index].getMemoryBankData().length() > 0) {
Log.d(TAG, " Mem Bank Data " + myTags[index].getMemoryBankData());
}
}
}
}
}
When I'm scanning a tag I get the correct TagID but both myTags[index].getOpCode() and myTags[index].getOpStatus() return null values.
I appreciate every suggestion that might lead to a successful scan.
Thanks.

I managed to find a solution for my problem. To perform any Read or Write task with Zebra Handheld Scanners the following two conditions must be satisfied. Look here for reference: How to write to RFID tag using RFIDLibrary by Zebra?
// make sure Inventory is stopped
reader.Actions.Inventory.stop();
// make sure DPO is disabled
reader.Config.setDPOState(DYNAMIC_POWER_OPTIMIZATION.DISABLE);
You have to stop the inventory and make sure to disable dpo in order to get data other than the TagID from a Tag. Unfortunately this isn't mentioned in the docu for Reading RFID Tags.

Firebase database pagination scrolling action

I'm following the tutorial:
https://codelabs.developers.google.com/codelabs/firebase-android/#6
I was trying to achieve pagination, Here is what i have modified:
...
Query query = databaseRef.limitToLast(50);
...
FirebaseRecyclerOptions<FriendlyMessage> options =
new FirebaseRecyclerOptions.Builder<FriendlyMessage>()
.setQuery(query, parser)
.build();
...
Here is the scrolling code as tutorial as default:
mFirebaseAdapter.registerAdapterDataObserver(new
RecyclerView.AdapterDataObserver() {
#Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);
int friendlyMessageCount = mFirebaseAdapter.getItemCount();
int lastVisiblePosition =
mLinearLayoutManager.findLastCompletelyVisibleItemPosition();
// If the recycler view is initially being loaded or the
// user is at the bottom of the list, scroll to the bottom
// of the list to show the newly added message.
if (lastVisiblePosition == -1 ||
(positionStart >= (friendlyMessageCount - 1) &&
lastVisiblePosition == (positionStart - 1))) {
mMessageRecyclerView.scrollToPosition(positionStart);
}
}
});
mMessageRecyclerView.setAdapter(mFirebaseAdapter);
Now the screen shows only 50 messages.
But it don't scroll to the bottom when new messages coming.It works fine before using query.
I want to know where should I start to modified.
Thank you.

From the swift side:
By changing the startKey, we can query the data from where we want(from the end of the database) and achieve the pagination by scrolling to the top of the screen.
if (startKey == nil){
print("firebasetest_startkey: ",self.startKey)
// for first grabbing data operation
_refHandle = self.ref.child(channel_title).queryOrderedByKey().queryLimited(toLast: 30).observe(.value){(snapshot) in
guard let children = snapshot.children.allObjects.first as? DataSnapshot else{return}
if (snapshot.childrenCount > 0){
for child in snapshot.children.allObjects as! [DataSnapshot]{
if(!(self.messageKeys.contains((child as AnyObject).key))){
self.messages.append(child)
self.messageKeys.append(child.key)
self.itemTable.insertRows(at: [IndexPath(row: self.messages.count-1, section: 0)], with: .automatic)
}
}
self.startKey = children.key
}
}
}else if (dragdirection == 0 && startKey != nil){
//going up
// for all other grabbing data operation from the bottom of the database
_refHandle = self.ref.child(channel_title).queryOrderedByKey().queryEnding(atValue: self.startKey).queryLimited(toLast: 10).observe(.value){(snapshot) in
guard let children = snapshot.children.allObjects.first as? DataSnapshot else{return}
if (snapshot.childrenCount > 0 ){
for child in snapshot.children.reversed(){
if ((child as AnyObject).key != self.startKey &&
!(self.messageKeys.contains((child as AnyObject).key))){
self.messages.insert(child as! DataSnapshot, at:0)
self.messageKeys.append((child as AnyObject).key)
self.itemTable.insertRows(at: [IndexPath(row: 0, section: 0)], with: .fade)
}
}
self.startKey = children.key
}
}
}

Data from Arduino to Processing isn't affecting Processing 'If Statement'

I'm trying to get a specific user's tweets into Processing and then have them spoken out using the TTS Library, but only have them spoken when a specific value is detected from Arduino over Serial = 491310
I've got the tweets coming into Processing and can have them printed and spoken, and the value 491310 is picked up by Processing, BUT it's the placement of the if Statement ( 'if (sensor == 491310) {') that I'm struggling with, as it currently has no effect - Can anyone solve this one?
Absolute novice here, any help would be great. Thanks.
import twitter4j.util.*;
import twitter4j.*;
import twitter4j.management.*;
import twitter4j.api.*;
import twitter4j.conf.*;
import twitter4j.json.*;
import twitter4j.auth.*;
import guru.ttslib.*;
import processing.serial.*;
TTS tts;
Serial myPort;
int sensor = 0;
void setup() {
tts = new TTS();
myPort = new Serial(this, Serial.list()[0], 9600);
}
void draw() {
ConfigurationBuilder cb = new ConfigurationBuilder();
cb.setOAuthConsumerKey("XXXX");
cb.setOAuthConsumerSecret("XXXX");
cb.setOAuthAccessToken("XXXX");
cb.setOAuthAccessTokenSecret("XXXX");
java.util.List statuses = null;
Twitter twitter = new TwitterFactory(cb.build()).getInstance();
String userName ="TWITTER HANDLE";
int numTweets = 19;
String[] twArray = new String[numTweets];
try {
statuses = twitter.getUserTimeline(userName);
}
catch(TwitterException e) {
}
if( statuses != null) {
for (int i=0; i<statuses.size(); i++) {
Status status = (Status)statuses.get(i);
if (sensor == 491310) {
println(status.getUser().getName() + ": " + status.getText());
tts.speak(status.getUser().getName() + ": " + status.getText());
}
}
}
}
void serialEvent (Serial myPort) {
int inByte = myPort.read();
sensor = inByte;
print(sensor);
}

Reading from a serial port returns a byte( 8 bit) not a 16 bit integer. The value of 'sensor" cannot be above 255 so never matches 491310. You'll have to do 2 reads to form the 16 bit int.

My guess is that you're hitting twitter's rate limit. Twitter only allows a certain amount of API calls in a given 15 minute window. And since you're calling getUserTimeline() in the draw() function (which happens 60 times per second), you're going to hit that limit pretty fast.
So you're probably getting a TwitterException, but you're just ignoring it. Never use an empty catch block! At least put a call to e.printStackTrace() in there:
catch(TwitterException e) {
e.printStackTrace();
}
To fix the problem, you're going to have to modify your code to only check for tweets once at the beginning of the program. Move all of your logic for fetching the tweets into the setup() function, and then move the logic for printing them out into the serialEvent() function.
If you still can't get it working, then you're going to have to do some debugging: what is the value of every single variable in your sketch? Use the println() function to help figure that out. Is statuses == null? What is the value of statuses.size()? What is the value of sensor? Once you know that, you'll be able to figure out exactly what's going wrong with your code. But my bet would be it's the twitter rate limit, so check that first.

Max 20 Friends Information on Twitter4J

Like you see in this code, I want to get all the information about friends in twitter, people I follow.
But doing this :
PagableResponseList<User> users = twitter.getFriendsList(USER_ID, CURSOR);
... only gives me the first 20 recent friends... What can I do?
Complete code about it :
PagableResponseList<User> users = twitter.getFriendsList(USER_ID, CURSOR);
User user = null;
max = users.size();
System.out.println("Following: "+max);
for (int i = 0 ; i < users.size() ; i++){
user = users.get(i);
System.out.print("\nID: "+user.getId()+" / User: "+user.getName()+" /");
System.out.print("\nFollowers: "+user.getFollowersCount()+"\n");
tid.add(Long.parseLong(String.valueOf(user.getId())));
tusername.add(user.getName());
tfollowers.add(Long.parseLong(String.valueOf(user.getFollowersCount())));
tname.add(user.getScreenName());
}
Thanks..

you can try this code to get the list of people you follow.
long cursor = -1;
PagableResponseList<User> users;
while ((cursor = followers.getNextCursor()) != 0);
{
users = twitter.getFriendsList(userId, cursor);
}

I've taken a peek at the documentation at Twitter4J and Twitter themselves and it's all about that cursor.
To prevent you're getting loaded with a whole bunch of friends at once, Twitter only returns the first 20 results. It doesn't return just the first 20 results, but it also returns a cursor. That cursor is just a random number that's managed by Twitter. When you make a call again and pass this cursor, the next 20 entries (friends) will be returned, again with a cursor that's different now. You can repeat this until the cursor returned is zero. That means there are no more entries available.
In case you want to know more, check these two links: Twitter DEV and Twitter4J documentation.
Concerning your Java, you just need to find a way to get the current cursor, and pass that cursor to your method again, making the app load the next 20 entries. According to this piece of information, that should do the trick.
List<User> allUsers = new ArrayList<User>();
PagableResponseList<User> users;
long cursor = -1;
while (cursor != 0) {
users = twitter.getFriendsList(USER_ID, cursor);
cursor = users.getNextCursor();
allUsers.add(users);
}

You should be able to request up to 200 results at a time:
final PagableResponseList<User> users = twitter.getFriendsList(USER_ID, cursor, 200);
cursor = users.getNextCursor();
If you need to start from where you left off between invocations of your program then you need to store the value of cursor somewhere.

Improvements to Sander's answer!
You can set a count value to the getFriendsList method as in Jonathan's Answer. The maximum value allowed for count is 200. The loop construct will help to collect more than 200 friends now. 200 friends per page or per iteration!
Yet, there are rate limits for any request you make. The getFriendsList method will use this api endpoint: GET friends/list which has a rate limit of 15 hits per 15 minutes. Each hit can fetch a maximum of 200 friends which equates to a total of 3000 friends (15 x 200 = 3000) per 15 minutes. So, there will be no problem if you have only 3000 friends. If you have more than 3000 friends, an exception will be thrown. You can use the RateLimitStatus class to avoid that exception. The following code is an example implementation to achieve this.
Method 1: fetchFriends(long userId)
public List<User> fetchFriends(long userId) {
List<User> friends = new ArrayList<User>();
PagableResponseList<User> page;
long cursor = -1;
try {
while (cursor != 0) {
page = twitter.getFriendsList(userId, cursor, 200);
friends.addAll(page);
System.out.println("Total number of friends fetched so far: " + friends.size());
cursor = page.getNextCursor();
this.handleRateLimit(page.getRateLimitStatus());
}
} catch (TwitterException e) {
e.printStackTrace();
}
return friends;
}
Method 2: handleRateLimit(RateLimitStatus rls)
private void handleRateLimit(RateLimitStatus rls) {
int remaining = rls.getRemaining();
System.out.println("Rate Limit Remaining: " + remaining);
if (remaining == 0) {
int resetTime = rls.getSecondsUntilReset() + 5;
int sleep = (resetTime * 1000);
try {
if(sleep > 0) {
System.out.println("Rate Limit Exceeded. Sleep for " + (sleep / 1000) + " seconds..");
Thread.sleep(sleep);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
By doing so, your program will sleep for some time period based on the rate limiting threshold. It will continue to run from where it left after the sleep. This way we can avoid our program stopping in the midway of collecting friends counting more than 3000.

I have the solution to my post... thanks to Sander, give me some ideas...
The thing was change the for to while ((CURSOR = ids.getNextCursor()) != 0);.
And... user = twitter.showUser(id);
Playing with showUser makes it possible to get, with a slowly time, all the info about all my friends...
That's all. Don't use user.get(i);

Update doesn't work when using ContentResolver to update Contact Groups

I have this code for update:
public Boolean update() {
try {
data.put(ContactsContract.Groups.SHOULD_SYNC, true);
ContentResolver cr = ctx.getContentResolver();
Uri uri = ContentUris.withAppendedId(ContactsContract.Groups.CONTENT_URI, Long.parseLong(getId()));
int mid = cr.update(uri, data,_ID+"="+getId(), null);
// notify registered observers that a row was updated
ctx.getContentResolver().notifyChange(
ContactsContract.Groups.CONTENT_URI, null);
if (-1 == mid)
return false;
return true;
} catch (Exception e) {
Log.v(TAG(), e.getMessage(), e);
return false;
}
}
I have values in data, I double checked, and for some reason the values are nut pushed out. I also ran a cur.requery(); and I am having
<uses-permission android:name="android.permission.WRITE_CONTACTS"></uses-permission>
EDIT 1
One thing to mention, that I need to use:
data.put(ContactsContract.Groups.SHOULD_SYNC, 1);
as the true value there is not accepted, although that is returned when you check the ContentValues.

Ok, I figured it down too:
SQLiteException: no such column: res_package: , while compiling: UPDATE groups SET sync4=?, sync3=?, sync2=?, group_visible=?, system_id=?, sync1=?, should_sync=?, deleted=?, account_name=?, version=?, title=?, title_res=?, _id=?, res_package=?, sourceid=?, dirty=?, notes=?, account_type=? WHERE _id=20
The weird thing is that, this column is returned when you Query the content provider. I made the queries to use all returned columns, so I need to make this work somehow.

I just made something similar work. Instead of
int mid = cr.update(uri, data,_ID+"="+getId(), null);
use
int mid = cr.update(uri, data,null, null)
your uri already has embedded ID information.