May 302016

When using Unity8 these days connecting a Bluetooth mouse to a device enables windowed mode. Another option is to connect an external monitor via HDMI and most recently on some devices wireless displays. This raises a few questions on the API side of things.

Apps are currently advised to use a MainView as the root item, which can have a width and a height used as the window dimensions in a windowed environment – on phones and tablets by default all apps are always full screen. As soon as users can freely resize the window, some apps may not look great anymoreQtQuick.Window solves this by providing minimum/maximum/Width/Height properties. Another question is what title is used for the window – as soon as there is more than one Page that’s no longer obvious and it’s actually somewhat redundant.

So what can we do now?

There’s two ways to sort this that we’ll be discussing here. One way is to in fact go ahead and use MainView, which is just an Item, and put it inside a Window. That’s perfectly fine to do and that’s a good stop-gap for any apps affected now. To the user the outcome is almost the same, except the title and sizing can be customized behind the scenes.

import QtQuick 2.4
import QtQuick.Window 2.2
import Ubuntu.Components 1.3
Window {
    title: "Hello World"
    MainView {
        applicationName: "Hello World"

From here on after things work exactly the same way they did before. And this is something that will continue to work in the future.

A challenger appears

That said, there’s another way under discussion. What if there was a new MainWindow component that could replace the MainView and provide the missing features out of the box? Code would be simpler. Is it worth it, though, just to save some lines of code you might wonder? Yes actually. It is worth it when performance enters the picture.

As it is now, MainView does many different things. It displays a header for starters – that is, if you’re not using AdaptivePageLayout to implement convergence. It also has automaticOrientation API, something the shell does a much better job of these days. And it handles actions, which are, like the header, part of each Page now. It’s still doing a good job at things we need, like setting up folders for confinement (config, cache, localization) and making space for the OSK (in the form of anchorsToKeyboard). So in short, there’s several internals to re-consider if we had a chance to replace it.

Even more drastic would be the impact of implementing properties in MainWindow that right now are context properties. “units” and “theme” are very useful in so many ways and at the same time by design super slow because of how QML processes them. A new toplevel component in C++ could provide regular object properties without the overhead potentially speeding up every single use of those properties throughout the application as well as the components using them behind the scenes.

Let’s be realistic, however, these are ideas that need discussion, API design and planning. None of this is going to be available tomorrow or next week. So by all means, engage in the discussions, maybe there’s more use cases to consider, other approaches, it’s the one component virtually every app uses so we better do a good job coming up with a worthy successor.

Ubuntu App Developer Blog: Can I haz MainView in a Window?
Source: Planet Ubuntu