My list picker is empty after i turn on my device but it worked before

[Alen_Popovic]

did i do something wrong or does the bluetooth part of the code needs to be updated

[Patryk_F]

I don't think these blocks are built in AppInventor...

[Alen_Popovic]

i mean i posted a screenshot i dont know how and why it wouldnt work it worked 6 months prio to this i followed a guide on youtube i dont know how your comment is helping here i thought i did something wrong

[Patryk_F]

The thing is, this community is for people who use AppInventor to build their apps. Usually every builder has a community and if you have any problem with your app, you should ask in the community with your builder. This is due to the differences that may be in different builders. What works here may not necessarily work in another builder, and vice versa. Besides, posts with the problem you are asking about appear here very often, several times a week. I think if you use the search engine, you will find the answer to your question in a few seconds.

[ABG]

Be sure to use println() at the end of each message to send from the sending device, to signal end of message.

Only use print() in the middle of a message.

Be sure not to println() in the middle of a message, or you will break it into two short messages and mess up the item count after you split the message in AI2.

Do not rely on timing for this, which is unreliable.

In the AI2 Designer, set the Delimiter attribute of the BlueTooth Client component to 10 to recognize the End of Line character.

Also, return data is not immediately available after sending a request,
you have to start a Clock Timer repeating and watch for its arrival in the Clock Timer event. The repeat rate of the Clock Timer should be faster than the transmission rate in the sending device, to not flood the AI2 buffers.

In your Clock Timer, you should check

  Is the BlueTooth Client still Connected?
  Is Bytes Available > 0?
     IF Bytes Available > 0 THEN
       set message var  to BT.ReceiveText(-1) 

This takes advantage of a special case in the ReceiveText block:

ReceiveText(numberOfBytes)
Receive text from the connected Bluetooth device. If numberOfBytes is less than 0, read until a delimiter byte value is received.

If you are sending multiple data values per message separated by | or comma, have your message split into a local or global variable for inspection before trying to select list items from it. Test if (length of list(split list result) >= expected list length) before doing any select list item operations, to avoid taking a long walk on a short pier. This bulletproofing is necessary in case your sending device sneaks in some commentary messages with the data values.

Some people send temperature and humidity in separate messages with distinctive prefixes like "t:" (for temperature) and "h:" (for humidity).
(That's YAML format.)

The AI2 Charts component can recognize these and graph them. See Bluetooth Client Polling Rate - #12 by ABG

To receive YAML format messages, test if the incoming message contains ':' . If true, split it at ':' into a list variable, and find the prefix in item 1 and the value in item 2.