Xamarin Mobile Application Development for Android - Second Edition

Adding validation

Any nontrivial app will have some level of the validation required. The POIApp app is somewhat trivial, but we have a small set of rules we need to enforce that will facilitate the discussion:

Property	Rule
Name	This cannot be empty or null
Latitude	This contains a valid decimal number between -90 and 90
Longitude	This contains a valid decimal number between -180 and 180

Using the EditText.Error property

The EditText widget has a string property named Error, which simplifies the effort of displaying errors to the user, particularly if you want to be able to show all the fields with errors at once. The following screenshot displays the error received for leaving the Name field empty:

To use this facility, simply ...