Consider eliminating public static references

[matthew-carroll]

I just submitted a PR with some new functionality for this package. In the process of extending this package and attempting to write tests, I noticed that this package relies on static members to query and notify clients of keyboard changes.

I would like to suggest migrating away from public static members.

Static members often interfere with testing practices. This is especially true for plugins where a connection is expected with the platform side. Such a connection is not easily faked.

In my PR I introduced a pretty ugly hack to facilitate a few simple tests. This was the result of those public static members.

An alternative to public static members is to provide only a singleton reference at the static level. For example:

final KeyboardVisibility keyboardVisibility = KeyboardVisibility.instance;
print('Is visible: ${keyboardVisibility.isVisible}');

With a singleton instance, one can replace the entire instance with a fake instance within tests. This avoids polluting the primary API surface with methods that should only be invoked during tests. It also lowers the likelihood that someone will inadvertently invoke a test method during production.

You can see this practice within Flutter if you look at bindings, for example:

WidgetsBinding.instance;
ServicesBinding.instance;

[tuononh]

Does this package even works? I just tried latest version 3.0.0 and it is not working on Android ☹️

[matthew-carroll]

@tuononh looks like that issue is discussed here: #19