Add functionality for providing values (DI)

[y9vad9]

Problem

I don't think it's necessary to add something to ViewScope<T> every time we need to use some common values. Also, there should be a way to provide instances as DI does.

Solution

I think in this case we should divide types of instances we provide. So, I propose next types of instances:

• static – initializes on application init and never changes (for example, ApplicationInstance)
• local – initializes in specific scope (for example, LocalContext that is unique for each view)
• mutable – can be changed while program runs (for example, AccountInstance where account can change due to log in / log out)

Providing instances

To provide instance, we use provider function, for example:

class Account(val name: String)
val AccountInstance = instance<Account?> { error("Not yet initialized") }

internal fun ViewGroupScope<*>.AppView() {
    provider(AccountInstance provides Account("test")) {
        AccountView()
    }
}

Getting instances

To get instance, we just call corresponding instance in ViewScope<T>:

internal fun ViewGroupScope<*>.AccountView() {
    frameLayout(frameLayoutParams().maxSize()) {
        AccountInstance.state.constructOnEach { account ->
            if (account != null) {
                textView {
                    text("Hello, ${account.name}!")
                }
            } else {
                button(layoutParams().width(64.dp)) {
                    text("Sign in")
                    gravity(Gravity.CENTER)
                }
            }
        }
    }
}

It's important to have ViewScope<T>, because it stores instanceProvider: InstanceProvder.