Creating my own extension blocks for App Inventor

MIT App Inventor for efficiently developing mobile applications has functions named Extensions that users can develop their own blocks. If you know Java, in principle you can do that, but in fact it's not so easy. Development methods for Extensions are presented in several sites, among which the AppyBuilder Code Editor shown in the following is extremely easy to use and useful:
https://amerkashi.wordpress.com/2018/11/26/appybuilder-code-editor/
http://Editor.AppyBuilder.com

Anyway, here we will create a simple and unique block with Extensions. The figure below is a hearing training application using English news. There is a counter to record how many times you have heard a particular news. Of course, even when resuming after turning off the power of smartphone, that counter must be continued. In other words, it must be created as a persistent counter.

Persistent counter in a real app

We will proceed with a simple application that extracts only this persistent counter portion as follows.

Persistent counter for an examination

If you use TinyDB, you can easily create such a counter as shown below. However, to do that, first you need to read the value of the counter (tag) from TinyDB, add 1 to it, and store the result in TinyDB again. This is very troublesome, because this counter is supposed to be used in many situations.

Persistent counter made with normal TinyDB (built-in)

To alleviate this complexity, we have created a new block to "count up one tag value" that is not found in the conventional Tiny DB. Including the original TinyDB functions, I made this name FoYoDB. As you can see, count-up part became very neat!

Persistent counter made with new FoYoDB (Extension)

In order to have versatility in this FoYoDB, we also made a block that allows you to arbitrarily specify "step value for counting up" as follows. This time, we created Extensions to extend original TinyDB, but from now on we would like to tackle the development of Extensions with higher originality.

All blocks created as an extension FoYoDB