How is it suggested to inherit from an implicit style in Xamarin.Forms XAML?

Question

I am having some issues inheriting from an implicit style defined in an Application ResourceDictionary. I have tried a couple of different approaches, but each has been unsuccessful in one form or another.

Attempt 1: Inherit from implicit style

Application ResourceDictionary

<Style TargetType="Button">
    <Setter Property="BackgroundColor" Value="#1386F1" />
    <Setter Property="TextColor" Value="White" />
    <Setter Property="FontAttributes" Value="Bold" />
    <Setter Property="HeightRequest">
      <OnPlatform x:TypeArguments="x:Double" iOS="30" Android="50" />
    </Setter>
    <Style.Triggers>
      <Trigger TargetType="Button" Property="IsEnabled" Value="False">
        <Setter Property="BackgroundColor">
          <OnPlatform x:TypeArguments="Color" iOS="#E8E8E8" />
        </Setter>
      </Trigger>
    </Style.Triggers>
</Style>

Page ResourceDictionary

<Style x:Key="LoginButtonStyle" TargetType="Button" BasedOn="{StaticResource {x:Type Button}}">
    <Setter Property="BackgroundColor" Value="#024886" />
    <Setter Property="Margin">
      <OnPlatform x:TypeArguments="Thickness" iOS="0,5" />
    </Setter>
</Style>

Page Control

<Button Style="{StaticResource LoginButtonStyle}" />

Result

Throws exception "StaticResource not found for key {x:Type Button}". This is how I remember doing it in WPF, but I'm assuming this isn't supported in Xamarin XAML.

Attempt 2: Inherit from common explicit style

Application ResourceDictionary

<Style x:Key="DefaultButtonStyle" TargetType="Button">
    <!-- Same as Attempt 1 -->
</Style>
<!-- This implicit style causes issues with the inheritence of the Trigger in the above explicit style. When it's commented out, everything works fine. -->
<Style TargetType="Button" BasedOn="{StaticResource DefaultButtonStyle}" />

Page ResourceDictionary

<Style x:Key="LoginButtonStyle" TargetType="Button" BasedOn="{StaticResource DefaultButtonStyle}">
    <!-- Same as Attempt 1 -->
</Style>

Page Control

<!-- Same as Attempt 1 -->

Result

Everything works except for the Trigger. However, when I remove the implicit style the Trigger magically starts working again. I'd rather not have to specify the explicit style on every Button, though. I believe this is just a bug, but I wanted to make sure before I take the time to prepare a bug report.

Any ideas?

Question in Xamarin Forums

Answer 1

First of all, thanks for the nice summary!

In my opinion this is a bug, which can be prevented with a little trick:

<!-- Base Style -->
<Style x:Key="BaseButtonStyle" TargetType="Button">
    <!-- Define base button style... -->
</Style>

<!-- Implicit Style -->
<Style TargetType="Button" BasedOn="{StaticResource BaseButtonStyle}"></Style>

<!-- Inherited Style -->
<Style x:Key="InheritedButtonStyle" TargetType="Button" BasedOn="{StaticResource BaseButtonStyle}">
    <!-- Extend base button style... -->
</Style>

Basically, the idea is to create a common explicit base style, which gets inherited by an implicit style afterwards. Therefore, all buttons are automatically applying the BaseButtonStyle, which is additionally extensible.

Attention: The implicit style has to be created after defining the base style.

EDIT: Apparently this is the same solution as #2 already provided before. So, the Trigger issue is not fixed, which seems to be a bug.