fix!: Allow to inherit from `View` to create custom classes

[susnux]

Use case: You want to scope logic and state into the view rather than somewhere in a module.

Problems: Currently there are two problem that prevent creating a child-class of view:

1. The view class did not implement the methods as methods but getters, this forces also child classes to use getters leading to really ugly code.
2. The constructor required getContents to be part of the ViewData, but for child classes this makes no sense, as you probably want to overwrite this with a member function instead. Fixed by checking if new View was called or a new subclass.

[codecov[bot]]

Bundle Report

Changes will increase total bundle size by 1.45kB :arrow_up:

Bundle name	Size	Change
@nextcloud/files-esm	118.08kB	722 bytes :arrow_up:
@nextcloud/files-esm-cjs	119.47kB	724 bytes :arrow_up:

[susnux]

This option is slightly breaking, but only for the files app as it need to check hasEmptyView before applying it as view.emptyView will now always be a function.

I think just extending View for custom views is more natural than just working with an data object (looses a bit of validation, but that is the risk of the implementor). But I am fine with any solution, and I have to admit the alternative in the PR below is simpler.

---

:information_source: See alternative PR here

[skjnldsv]

This option is slightly breaking, but only for the files app as it need to check hasEmptyView before applying it as view.emptyView will now always be a function.

Why not keep it as getter?

[susnux]

Why not keep it as getter?

Because you can not overwrite it in a custom class, it always then has to be a getter not a method. Meaning this would be not be allowed:

class MyView extend View {

    public emptyView(div: HTMLDivElement) {
        // do something
    }
}

Instead you would need to do:

class MyView extend View {

    public get emptyView() {
        return this.handleEmptyView.bind(this)
    }

    private handleEmptyView(div: HTMLDivElement) {
        // ...
    }
}

[susnux]

(Thats the reason I also offer the alternative: https://github.com/nextcloud-libraries/nextcloud-files/pull/1068 )

[skjnldsv]

Why would you need to overwrite it? you can already customize the emptyView function when you create the View instance?

[susnux]

Why would you need to overwrite it?

Because e.g. I want to have a local scope, meaning the emptyView should not just be a loose function but bound to my class, so that I can access (private) class properties. Meaning to be able to store view related state (e.g. the Vue instance of the empty view) inside of the View class instead being forced to store in in module scope.