Problem happened in making xylophone (record & playback)

MIT App Inventor Help
1

Hi! Today I want to make a xylophone recording and playing back notes. I know there is one tutorial in App Inventor, but I want to use my own coding instead. I will use another alternative way to store a song.
Here are the instructions: Xylophone Advanced.pdf (324.4 KB)
The assignment is proved difficult and I even don't know how to do it.
For the designer part:

Xylophone Designer
Xylophone Designer2157×1335 343 KB

I'll set some variables to do the process: lastPair, lastTime, song.
When I press any of the buttons, it will make a sound corresponding to the note.
The variables and procedures of the code:
Xylophone Variables & Procedures
Step 1 of the code: (I have no problem for that currently)
Xylophone Step 1
Xylophone Step 1803×471 29.8 KB

Step 2 of the code: (when one of the note buttons click, what will happen?)
Xylophone Step 2
Xylophone Step 2862×692 48.8 KB

Step 3 of the code: (most confusing :frowning: )
Xylophone Step 3
Xylophone Step 3669×617 42.4 KB

Here are all the codes that I have made.
But when I tested the app, it has a runtime error showing that the index originally need to change to 1 but the length of the list is 0...
Also, I cannot record or playback any of the notes, which is the most concerning for me.
It is complicated, and I don't know how to solve the problem or finish the app in success.
Thus, please help me or give me some advice! Thank you!

2

Please look at the instructions before replying to this post or otherwise you won't understand what's going on now. Thank you so much!

3

See here:

https://groups.google.com/g/mitappinventortest/c/Iu-tiC9GWgk/m/Xw3wdzFUBgAJ

4

Thank you for the link! However, I'm trying not following the instructions of App Inventor as I have it on my own. I want to have another alternative way to record and playback the song.

5

You need to debug this; impossible without the aia and guessing at the cause only by inspection. Use DoIt (see Enis's advice at MIT App Inventor 2 Tips – TWO DOG APPS ) What is apparently happening (a guess) is you attempt to use a List before the List is actually populated. The problem might be how you use your Clock. The order of the blocks in your PlayBackNote Procedure are also suspect. Your sound.source possibly should be in the if statement to prevent selecting a source inadvertently.

Also figure 15-5 in http://www.appinventor.org/bookChapters/chapter15.pdf may help you debug.

Keep on experimenting. :slight_smile: Realize, no one can test your app without an aia so you have to debug it.

6
  • From your blocks the if-statement is never true
  • global var lastTime is set to false and this cannot be used in a duration block

grafik
grafik1252×349 79.9 KB

7

Tysm! I will try to improvise the coding of the project using your suggestion!

8

Hello everyone! I've tried to improvise the project by correcting a few codes. Here is the project I have made with your suggestions.

  1. The variable last_time is changed to an invalid value initially. When the user presses the other button, the variable will change.
  2. I have corrected a few mistakes in the playback and timer section.

Here is the project attached:
Xylophone.aia (593.1 KB)
Please don't change it :slight_smile: Reply to this message if you have any comments on this! Tysm!

However, there are a few things I'm concerned about. Firstly, when I tested the project in the AI companion, it shows that there is a 701 and 703 error (Unable to load/Unable to play). Why is this happening? Thanks.

9

Read this first (especially point 3 and 4):

grafik
grafik863×211 17 KB