General approach to adaptive apps

So, just how do you approach taking an app designed for conventional mobile devices, and make it beautiful on a wide range of devices? What steps are required?

Google engineers, who have experience doing this very thing for large apps, recommend the following 3-step approach.

First, identify the widgets that you plan to make dynamic. Analyze the constructors for those widgets and abstract out the data that you can share.

Common widgets that require adaptability are:

• Dialogs, both fullscreen and modal
• Navigation UI, both rail and bottom bar
• Custom layout, such as "is the UI area taller or wider?"

For example, in a Dialog widget, you can share the info that contains the content of the dialog.

Or, perhaps you want to switch between a NavigationBar when the app window is small, and a NavigationRail when the app window is large. These widgets would likely share a list of navigable destinations. In this case, you might create a Destination widget to hold this info, and specify the Destination as having both an icon and a text label.

Next, you will evaluate your screen size to decide on how to display your UI.

You have two ways to determine the size of your display area: MediaQuery and LayoutBuilder.

In the past, you might have used MediaQuery.of to determine the size of the device's screen. However, devices today feature screens with a wide variety of sizes and shapes, and this test can be misleading.

For example, maybe your app currently occupies a small window on a large screen. If you use the MediaQuery.of method and conclude the screen to be small (when, in fact, the app displays in a tiny window on a large screen), and you've portrait locked your app, it causes the app's window to lock to the center of the screen, surrounded with black. This is hardly an ideal UI on a large screen.

Keep in mind that MediaQuery.sizeOf returns the current size of the app's entire screen and not just a single widget.

You have two ways to measure your screen space. You can use either MediaQuery.sizeOf or LayoutBuilder, depending on whether you want the size of the whole app window, or more local sizing.

If you want your widget to be fullscreen, even when the app window is small, use MediaQuery.sizeOf so you can choose the UI based on the size of the app window itself. In the previous section, you want to base the sizing behavior on the entire app's window, so you would use MediaQuery.sizeOf.

Requesting the size of the app window from inside the build method, as in MediaQuery.sizeOf(context), causes the given BuildContext to rebuild any time the size property changes.

LayoutBuilder accomplishes a similar goal as MediaQuery.sizeOf, with some distinctions.

Rather than providing the size of the app's window, LayoutBuilder provides the layout constraints from the parent Widget. This means that you get sizing information based on the specific spot in the widget tree where you added the LayoutBuilder. Also, LayoutBuilder returns a BoxConstraints object instead of a Size object, so you are given the valid width and height ranges (minimum and maximum) for the content, rather than just a fixed size. This can be useful for custom widgets.

For example, imagine a custom widget, where you want the sizing to be based on the space specifically given to that widget, and not the app window in general. In this scenario, use LayoutBuilder.

At this point, you must decide what sizing breakpoints to use when choosing what version of the UI to display. For example, the Material layout guidelines suggest using a bottom nav bar for windows less than 600 logical pixels wide, and a nav rail for those that are 600 pixels wide or greater. Again, your choice shouldn't depend on the type of device, but on the device's available window size.

To work through an example that switches between a NavigationRail and a NavigationBar, check out the Building an animated responsive app layout with Material 3.

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