Xamarin Forms ToolbarItem doesn't change IsEnabled from XAML - xamarin.forms

Question

I'm facing a problem with ToolbarItem and IsEnabled property when trying to turn it on/off from XAML using triggers. ToolbarItem doesn't support triggers, so what I do is to create a Button (a hidden one) which supports triggers and then bind Button.IsEnabled to ToolbarItem.IsEnabled; here is the sample code:
<ContentPage.ToolbarItems>
<ToolbarItem x:Name="tlbSave" Text="Save" Clicked="Handle_Clicked">
<ToolbarItem.IsEnabled>
<Binding Source="{x:Reference btnTest}" Path="IsEnabled" />
</ToolbarItem.IsEnabled>
</ToolbarItem>
</ContentPage.ToolbarItems>
<ContentPage.Content>
<StackLayout Padding="10" VerticalOptions="CenterAndExpand">
<Entry x:Name="txtTest" HorizontalOptions="FillAndExpand" />
<Button x:Name="btnTest" Text="HIDDEN" IsEnabled="false" HorizontalOptions="FillAndExpand">
<Button.Triggers>
<MultiTrigger TargetType="Button">
<MultiTrigger.Conditions>
<BindingCondition Binding="{Binding Source={x:Reference txtTest}, Path=Text.Length,
Converter={convert:IsPositiveIntegerConverter}}" Value="true" />
</MultiTrigger.Conditions>
<Setter Property="IsEnabled" Value="True" />
</MultiTrigger>
</Button.Triggers>
</Button>
</StackLayout>
</ContentPage.Content>
If you try this piece of code you will see how btnTest gets enable/disable when txtTest.Text has some value. But it isn't affecting tlbSave.IsEnabled property.
However, this work perfect in code behind when I set tlbSave.IsEnabled into btnText.PropertyChanged EventHandler
btnTest.IsVisible is false, I'm just showing it up for testing purposes.
Any idea about how to deal with this?

Answer 1

This is because of the IsEnabled property of ToolbarItem is read-only.
If you just set IsEnabled property of a toolbar item in your XAML to false or true, you will get the following exception at runtime.
System.InvalidOperationException: The BindableProperty "IsEnabled" is readonly.
And if you take a look at Microsoft's documentation, you will notice that you cannot directly set IsEnabled property of a toolbar item.
For disabling a toolbar item, the suggested way is to use a command and it's CanExecute.

Answer 2

I found out a way to solve this problem, at least a way better than implementing OnPropertyChange for btnTest
<ContentPage.ToolbarItems>
<ToolbarItem x:Name="tlbSave" Text="Save" Clicked="Handle_Clicked" />
</ContentPage.ToolbarItems>
<ContentPage.Content>
<StackLayout Padding="10" VerticalOptions="CenterAndExpand">
<Entry x:Name="txtTest" HorizontalOptions="FillAndExpand" />
<Button x:Name="btnTest" Text="HIDDEN">
<Button.Triggers>
<MultiTrigger TargetType="Button">
<MultiTrigger.Conditions>
<BindingCondition Binding="{Binding Source={x:Reference txtTest}, Path=Text.Length,
Converter={convert:IsPositiveIntegerConverter}}" Value="true" />
</MultiTrigger.Conditions>
<Setter Property="IsEnabled" Value="True" />
</MultiTrigger>
</Button.Triggers>
<Button.IsEnabled>
<Binding Source="{x:Reference tlbSave}" Path="IsEnabled" Mode="OneWayToSource" />
</Button.IsEnabled>
</Button>
</StackLayout>
</ContentPage.Content>
Then set btnTest.IsEnabled = false; inside constructor and everything will go as smooth as I want.