Xamarin Forms ToolbarItem doesn't change IsEnabled from XAML

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?

Why exactly are you using triggers? Curiosity! Also shouldn't your binding look something like `` — FreakyAli, Mar 10 '19 at 18:21

score 8 · Answer 1 · answered Mar 10 '19 at 20:54

8

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.

answered Mar 10 '19 at 20:54

Armin Rasoulian

271
1
9

2

In XAML we can't assign a boolean value to `IsEnabled` because it's a bindable property. However in code behind I can change its value. – Saimel Saez Mar 15 '19 at 15:04
"For disabling a toolbar item," does that work for you? I've seen bug reports from 2015 saying it doesn't disable based on CanExecute and still executes. I am on XF 4.4 and the CanExecute does not seem to be be respected even now – Pat Long - Munkii Yebee May 06 '20 at 14:49
From where do you see it's read only? There is a getter and a setter. The only notice I can see is *For internal use by the Xamarin.Forms platform.* – testing Apr 09 '21 at 13:22

score 2 · Answer 2 · answered Apr 04 '19 at 13:38

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.

Xamarin Forms ToolbarItem doesn't change IsEnabled from XAML

2 Answers2