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Ruboto Tip: Styling Interface Widgets

My earlier Android Meets Ruby: Using Ruboto UI blog post described how to use newer Ruboto syntax when constructing your user interfaces. Ruboto also has support for styling your interface widgets, but you may run into some issues at runtime depending on your environment setup. Fortunately, a workaround is available.

Suppose we want to modify the Fishmonger app to include larger text, so customers can more easily read the prompts and order their fish. In standard Android, we would accomplish this with the following XML:

<TextView android:text=”What would you like to order?” style="@android:style/TextAppearance.Large"/>

In Java, you can accomplish the same task by providing the corresponding style attribute value to the constructor:

new TextView(this, null, android.R.attr.textAppearanceLarge);

Ruboto is adding similar support to its widget scripting. Instead of using kludgy Java syntax to replicate the above constructor, you’ll be able to use a more natural syntax:

text_view :text => 'What would you like to order?', :default_style => R::attr::textAppearanceLarge

However, when you run this script, you may encounter an error like the following when the app tries to create your UI:

04-17 21:40:17.789: I/System.out(9291): NoMethodError: private method `attr' called for Java::Android::R:Class
04-17 21:40:17.789: I/System.out(9291):               on_create at file:/data/app/us.cirion.fishmonger2-2.apk!/fishmonger2_activity.rb:29
04-17 21:40:17.789: I/System.out(9291):        linear_layout at (eval):20
04-17 21:40:17.789: I/System.out(9291):               on_create at file:/data/app/us.cirion.fishmonger2-2.apk!/fishmonger2_activity.rb:21
04-17 21:40:17.793: I/System.out(9291):   start_ruboto_activity at file:/data/app/us.cirion.fishmonger2-2.apk!/ruboto/activity.rb:49
04-17 21:40:17.793: I/System.out(9291):               (root) at file:/data/app/us.cirion.fishmonger2-2.apk!/fishmonger2_activity.rb:18

What’s going on here? There are several things to check for. First, make sure that you’re referencing the proper android.R, and not your project’s own .R class. The latter is usually referenced via Ruboto::R. You may also run into issues where ruboto or jruby try to grab the wrong field in R.

Fortunately, there’s a workaround available that uses a more verbose way of accessing this field:

@text_view = text_view :text => 'What would you like to order?', :default_style => JavaUtilities.get_proxy_class("android.R$attr")::textAppearanceLarge

This code will directly look up the attributes class through the proper package, and then retrieve your desired style value. While this admittedly looks just as kludgy as the constructor we’re trying to get away from, it still better fits the Ruboto way of constructing widgets by configuring the parameters. Hopefully you don’t ever need to solve this problem, but if you do, keep this escape hatch in mind.

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About this author

Chris King is a software engineer specializing in mobile development. He is the author of Advanced BlackBerry Development, Advanced BlackBerry 6 Development, and Android in Action, Third Edition. You can learn more about Chris at www.linkedin.com/pub/chris-king

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