Thursday, May 20, 2010

Supporting navigation with the trackball

Let's talk about using the trackball in android applications.

First of all I was surprised when noticed that focus (orange background) is not visible on ListView's items. During testing application I noticed that ListView items gets focus in reality, because if we click with the trackball on item appropriate event would be handled. However, we can't see focus that is why I started investigation. Finally it was found out that it is because of background
of ListView's items. If we need to see focus we must have background color's alpha parameter 0(ex. Color.argb(0,255,255,255), hex colors). But in that case we wouldn't have real colors(colors would be darker, ex. white would be gray). That is why we have to remove background color and use default black background. And also I want to mention another limitation of ListView. It's not possible to define items which must be focusable, because ListView is doing that itself.

The second thing that shocked me was that we can't see focus on ImageView item. In our "Edit Profile" page we have a lot of elements and have a method to define sequence of focused items. The focus works correctly for all elements, but ImageView is an exception. Investigation shows that it is a known issue that is why I have to put ImageView in another view, implement selector for that view and give orange background to it when it is focused.

Third I want to speak about behavior of the trackball under tabs. Let's go through an example.We have one activity which is responsible for drawing TabHost. Under each tab we have another activity. We need to be able to reach and interact with all items on all tabs using just the trackball. With our implementation it means that we have to navigate through items in different activities which, in my point of view, is not possible.That is why for now with the trackball we can only move slider and go from one tab to another.For example we need to set a focus on tab. As soon as activity under tab is loaded focus automatically will go to appropriate element under tab.That is why if we need to navigate through tabs we must first of all go up with the trackball then change tab.

That's all for now about strange behavior of focus when using the trackball.

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