How to make a trigger aware of a property change

Question

On a wpf window I have a button defined as follows:

<Button
    x:Name="btnDone"
    Content="Done">
    <Button.Style>
        <Style
            TargetType="Button">
            <Setter Property="Visibility" Value="Collapsed" />
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=IsDrawing}" Value="True">
                        <Setter Property="Visibility" Value="Visible" />
                    </DataTrigger>
                </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

The trigger property, IsDrawing, is defined as folows:

 Public IsDrawing As Boolean

When the user initiates drawing I set IsDrawing = True but the trigger does not make the button visible.

I have tried to make IsDrawing a dependency property of the window, adding a PropertyChanged event to the window and other - equally unsuccessful - ideas. None, however, make the trigger aware of the change.

How do I accomplish that?

Answer 1

Probably you made some mistakes or forgot to set the DataContext (which can be done in constructor or Load event, for example). Show some details.

The next fragments of MainWindow window seems to work.

XAML:

<Window x:Class="MainWindow"
        . . .
        Loaded="Window_Loaded">
    <Grid>
        <Button x:Name="btnDone" Content="Done" Margin="24,68,612,297">
            <Button.Style>
                <Style
             TargetType="Button">
                    <Setter Property="Visibility" Value="Collapsed" />
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding Path=IsDrawing}" Value="True">
                            <Setter Property="Visibility" Value="Visible" />
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </Button.Style>
        </Button>
        <Button x:Name="testButton" Content="test" HorizontalAlignment="Left" Margin="355,31,0,0" VerticalAlignment="Top" Width="75" Click="testButton_Click"/>
    </Grid>
</Window>

Class:

Class MainWindow

    Private Shared ReadOnly Property IsDrawingProperty As DependencyProperty = DependencyProperty.Register(NameOf(IsDrawing), GetType(Boolean), GetType(MainWindow))

    Public Property IsDrawing As Boolean
        Get
            Return CBool(GetValue(IsDrawingProperty))
        End Get
        Set(value As Boolean)
            SetValue(IsDrawingProperty, value)
        End Set
    End Property

    Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
        DataContext = Me
    End Sub

    Private Sub testButton_Click(sender As Object, e As RoutedEventArgs)
        IsDrawing = True
    End Sub

End Class

This example assumes that IsDrawing is a member of your window.