See the App Inventor Extensions document about how to use an App Inventor Extension.
For questions about extensions or bug reports, please start a new thread in the App Inventor Extensions forum. For feature requests please contact me by email. To be a sponsor of a new method already is possible starting from only 10 USD! With your contribution you will help the complete App Inventor community. Thank you.
While starting the companion app, all necessary assets and also the imported extensions of your project will be copied to your device.
So in case the no such class error shows up, the extension code to run the extension is not available on your device.
Without that code the companion app is not able to execute methods from the extension.
In case restarting the companion app does not work for you after trying several times, then as it looks like the only way for you to test you app will be after building it using the apk file.
Account Manager Extension to get some information about the user
AES Encryption Extension to encrypt/decrypt strings
Barometer Sensor Extension to get the current pressure and altitude
Battery Manager Extension to provide battery information
Billing Extension to use Google In-App Billing in your App Inventor app for Products (both non-consumable and consumable) and Subscriptions.
Classic Bluetooth Extension to enable/disable bluetooth without user interaction, scan, pair/unpair devices
Camera Extension to take pictures programmatically without user interaction.
Clipboard Extension to copy/paste text to/from the clipboard
2019-03 Exif Extension to read and write Exif tags in a JPEG file or a RAW image file.
File Extension is an extension related to the File component
Flashlight Extension to turn on/off the flashlight.
FTP Extension to upload or download files to/from your server via FTP
Headset Plug Status Extension to get the headset plug status.
Hotspot Extension to toggle wifi hotspot on or off.
Image Extension to do some basic image manipulation.
Image Metadata Extension to read the metadata of an image file
Light Sensor Extension to get the illuminance
Magnetic Sensor Extension to get magnetic X, Y, Z and absolute field strength
Simple Notification Extension to send a notification
Package manager Extension to get information about installed apps and to be able to launch an installed app using a package name.
Pdf Extension to open pdf files and render a specific page (without using an external app).
Settings Extension to get/set the brightness of the display and get/set/play a ringtone
Take Screenshot Extension to take a screenshot
Sharing Extension offers the functionality of the Sharing component with some modifications
Speech Recognizer Extension offers the functionality of the Speech Recognizer component and some additional blocks
SQlite Extension to access the local SQlite database
Telephony Manager Extension to get some information from the telephony manager.
2019-03 Ambient Temperature Sensor Extension to get the ambient temperature in Celcius.
Textbox Extension to get/set cursor position, to highlight text, to have an event, which fires after text changed
Texting Extension, read all SMS from the inbox, draft and sent folders.
Tools Extension, a collection of several tools, which do not need additional permissions.
WiFi Extension offers some useful blocks to use in a wireless lan
Zip Extension to zip/unzip files.
More details on how these blocks work can be found here.
Note: You only can use one extension developed by this developer for a specific project. Using more as one extension results in DX execution failed error. The developer seems to be not very interested in fixing this bug for the community, it would take him only 5 minutes... For details see also here.
Note: To be able to get some of these extensions, you have to pay in MitCoins (a virtual currency of that webpage)
This work by Pura Vida Apps is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License
with attribution (name=Pura Vida Apps and link to the source site) required.