Error help! plz ---segment: start(3) + length(8) - 1 exceeds text lenght(0)

MIT App Inventor Help
1

Hello I am making an app with a project. I'm getting this error rather than anything else, can you tell me how to fix it?

KakaoTalk_20230526_114737218
KakaoTalk_20230526_1147372181124×703 49.6 KB

KakaoTalk_20230526_114751037
KakaoTalk_20230526_1147510371087×555 43.1 KB

2

Hello there,

Please change the language of your blocks to English, then download a high-quality image of your blocks by right-clicking your blocks and selecting Download Blocks as Image.

3

Please see the Delimiter article in FAQ

Be sure to use println() at the end of each message to send from the sending device, to signal end of message. 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.
BlueToothClient1_Properties
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.

4

I might not be good in these, but in "When Timer" event block why did you leave that "Set Global 1 to receive text numberOfBytes" empty?

5

maybe...if you...probably check the empty blocks like the number of bytes just set it to 0?

6

I'm not sure, but there should be a warning then.

1 Like
7

hmm maybe they should show the warning signs.

OP, can you please tell us whether you are getting a warning icon count at the end of the blocks?

8

Well, it can only be shown when "show Warnings" is clicked.

1 Like