In a complete manifest, the preceding might look like this: Remember that you just provide the class’s canonical name, and instantiation, references, and setup are performed in the background automagically (meaning the process is entirely opaque to us as developers or users). This Activity entry should also include an action name equal to, which should be present for any of your app’s entry points (e.g., launcher icon, deep link, system-wide broadcast, etc.). Once application initialization is complete, the application will launch a single instance of the Activity class that you defined in your application manifest with the value for its category node. However, you’re free to perform asynchronous work on your own background threads at this time. Again, it’s extremely important to remember that this is happening on the main (UI) thread, so this will block anything else from happening. Note that if you provide a custom Application class for your app, anything in the onCreate method will happen at this time. This work occurs on the main thread and cannot be preempted or interrupted-it’s just going to happen. When your app launches, it will perform some initialization logic, during which time you’ll see the “window background” (usually just a solid color, depending on your screen, but this can be set to any valid Drawable instance). How to Create Your App’s Starting UI Controller When in doubt, we’ll defer to the prevalent, existing patterns-launching new Activity instances, passing data as Bundle instances of primitive information, and managing modular content with Fragment instances and Activity controller methods, rather than the newer Navigation architecture component and its siblings. We won’t take a side, so we will show the basics of both approaches. That said, we know there are a lot of legacy apps out in the wild that do not use the pattern and don’t plan on re-architecting several years of work to conform to it. There are valid arguments for both sides, but since Google is the maintainer of Android, we believe we need to accede to its recommendation going forward. In fact, even today the Android dev-docs start the chapter on Activity with this:Īn activity is a single, focused thing that the user can do. Note that this goes against recommended practices that have been provided since Android was launched over a decade ago, where an Activity was recommended for any “activity” (roughly approximate to a “screen” or a single web page), and nesting Fragments was intermittently (!) discouraged. The new Navigation component released in the Jetpack suite should be used to manage interactions between fragments and display history. Less than a year prior to the time of this writing, Google announced that its recommended style of navigation was for an application to use a single Activity instance, and Fragment class instances within that single Activity to represent operations and manage views. Let’s learn about some core tasks in this area that are central to both platforms. Fortunately, both Android and iOS have provided some common tools and abstractions to handle the heavy lifting of this process. In a sense, it’s the heart of any app.Īll of this juggling requires an incredibly complex series of events with one technology built on top of another, operating in concert. The presentation of the UI-how it’s rendered on the screen-is usually controlled by layout instructions (often markup, like XML or HTML) the UI Controller acts as the bridge between input commands, database queries, IPC requests, messages, and much more. It would be ushering actors out to the stage, taking commands from the director, and helping transition between scenes.Īny time you want to display an image, list, or piece of text in an app, you’ll need a UI. If your application were a Shakespearean play put on in some elaborate, Old World theater, the UI controller would play the part of stage manager. User interface (UI) controllers serve as a connection between your UI and any business logic in your application that controls, or is instructed by, that UI.
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