Functional Reactive Programming in Android using RxAndroid has been talked about a lot recently in the Android community. It is great for for cleaning up a variety of aspects of Android programming, but in this post I'm going to focus on form validation (exciting, right?). The problem that needs to be solved is showing in-line error messages on a payment form and enabling a button if all input forms check out. Observing character changes on the EditTexts, using the new Design Support Library's InputFieldLayouts, and making use of some nifty RxAndroid operators makes solving this problem pretty simple. We'll be using the RetroLambda plugin to give us lambda support for RxJava.
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This post assumes some knowledge of how RxJava and lambdas work. If you need more of a refresher[]