android-如何构建可以拉伸的复杂视图？

Question

I'm at the planning stages of my first proper android app. Part of the brief is to have a very "good looking" interface (aka, plenty of graphics). As I'm a web developer, and I'm used to the CSS way of doing things, I'm struggling to understand how I will cater for all the different resolutions when building my layouts. To cut it short, my question is this: how do I build complex, image heavy views that can be seen in apps such as SoundHound (example view here, for those not familiar with this app: http://getandroidstuff.com/wp-content/uploads/2010/09/SoundHound-Android2.jpg )? Is there a way I can tile images in a similar way to the way I'd tile in CSS?

Answer 1

It is important that you know how all Layouts Views work before you start designing your main layout. Android OS by very design supports stretching of views and GroupViews. You need to use dp (density independent pixel) units.

In the example you provided, there are some nice nine patch PNGs. Check C:\\android-sdk-windows\\tools\\draw9patch.bat if on PC. These pngs stretch properly as backgrounds for any resolution.

Linear layout have weight which allows you determine how much space will each child occupy, similar to the old column width for tables in %. Just like in old hml, to make a rich layout you use nested GroupViews (eg LinearLayout, RelativeLayout etc) and populate them with children views like ImageView, TextView and son on.

It is possible also to have text styled with <b>,<i> tags and have

<img src="DrawableName">

see an example: Html.ImageGetter

Opposite to a nested layout would be to use the RelativeLayout and determine the position of each child view by its top and left margin anywhere on the screen in relation to the top-left corner of their parent RelativeLayout.

Answer 2

Android has some conventions, that help you out when it comes to different screen sizes, screen densities, screen ratios ...

For example there is a directory called "drawable" where you can put the image resources for your application. However, if you want to ship your application for devices with different resolutions, you can create additional folders named "drawable-ldpi", "drawable-mdpi", "drawable-hdpi". The ldpi folder contains image resources for low density screens, mdpi is meant for medium density and hdpi meant for high density. The folder names are part of the Android conventions. When loading an image resource at runtime eg on a high density device, the system is looking for the image resource in the drawable-hdpi folder. It there is no image with that name, the system will look in the drawable folder.

This concept also applies to the xml layouts you define in your "layout" folder. Maybe you say that the layout homeScreen.xml needs to look different when the user switches from portrait to landscape mode. Then you can create a folder "layout-land". You create another homeScreen.xml in there and change its apperance to your needs. At runtime the system detects the current mode. If in landscape, it will first check if there ist a folder "layout-land" and if it contains the layout file with the correct name. If not, or when the user switches back in portrait mode and there is no folder "layout-port", the system looks for the layout file in the "layout" folder.

This is only a small part of it, but I hope, you got a first glance and everything was understandable. Further information can be found in the official refrence