[SOLVED] The BindableProperty "Triggers" is readonly

Oliver Brown
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TLDR: When setting the Triggers property in XAML, use the actual type of the parent tag, not a supertype.

After recently updating Xamarin Forms from 2.3.2.127 to 2.3.3.175, I started getting an InvalidOperationException: The BindableProperty "Triggers is readonly" inside InitializeComponent. Unlike many problems, this was quite easy to track down. InitializeComponent errors are generally XAML, and in the page in question there was a single Trigger. In this case the solution was simple. The Trigger was on a custom Button type, but I was setting it specifically using Button.Triggers. Changing it to be the actual type fixed it. So, I changed it from

<local:MyButton>
  <Button.Triggers>
    <DataTrigger ... />
  </Button.Triggers>
</local:MyButton>

to

<local:MyButton>
  <local:MyButton.Triggers>
    <DataTrigger ... />
  </local:MyButton.Triggers>
</local:MyButton>

I believe the original should be valid (and previously was) but the change is simple enough to not be a big problem.