It is much more flexible to provide the container with a set of preprepared View objects because then the container simply has to display the View object without having to perform any conversions.Īll containers that derive from the AdapterView class make use of adapters to supply what they display in terms of View objects. If you wanted to display a list of images, say, then you would need a ListView that understood images and so on. Things could be organized in this way and it would be simpler - but only if you wanted to display Strings. You might be wondering why not just supply a set of Strings to the ListView and let it work out how to display the Strings as text? For example, a ListView has horizontal slots, one per item and a GridView has a 2D grid of slots.Įach container accepts a View object and displays it in a slot.įor example, you could provide the ListView with TextView objects and it would simply display text in each of its slots. The container has various positions that are visible on the screen for displaying items. The Adapterĭisplaying a collection of items has a number of similarities no matter what the collection of items are or what container is used. It is the View object that the container displays for each item of data in the collection. The key idea is that to display a collection each item in the collection has some how to be converted to an appropriate View object.
Well it does make it easier once you understand how it all works. When the user selects an item they are then presented with more details of the item - a details view.ĭisplaying lists and other collections of data is so common that Android has a mechanism that makes it easier.
Because of the limited screen size it is often the case that the user can only be shown an overview of quite a few different items. Android and portable devices often need something more than just a small list. If you are familiar with desktop development then you probably think of lists that the user can select from as being similar to a drop-down list. We have already looked at the basic Picker in chapter 12 but the ListView is a more general category of "picker". If you are interested in creating custom template also see:įor a range of reasons, one of the most common things you need to do in an Android UI is to display a list of things that the user can select from.
Third Edition Is now available in paperback and ebook. It isn't difficult to use, but you need to get to grips with the idea of an "adapter" and understanding what is going on pays dividends. ListView is probably the most commonly used and needed UI components in an Android app.
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