WPF - 将 UserControl 可见性绑定到属性

Question

I have a ListView bound to ObservableCollection. Data are loaded from the internet and then added to collection. The download takes few seconds and I want to indicate user that the data is loading.

I created an UserControl that indicates activity. I placed it inside of ControlTemplate.

<ControlTemplate x:Key="ListViewControlTemplate1" TargetType="{x:Type ListView}">
    <Grid>
        <local:ActivityIndicatorControl 
            HorizontalAlignment="Center" 
            Height="Auto" 
            Margin="0" 
            VerticalAlignment="Center"/>
    </Grid>
</ControlTemplate>

I would like to bind Visibility of ActivityIndicatorControl to a property, let's say bool IsLoading and set it to Visible/Collapsed correspondingly.

Thanks!

Answer 1

I would recommend using a IValueConverter to accept your boolean, and return a member of Visibility enumeration.

Here is a good example of one: http://jeffhandley.com/archive/2008/10/27/binding-converters---visibilityconverter.aspx

The XAML would look like this:

First you define a resource for the converter (put this in a resource dictionary):

<local:BooleanToVisibilityConverter x:Key="myBoolToVisibilityConverter" />

And then change your template like this:

<ControlTemplate x:Key="ListViewControlTemplate1" TargetType="{x:Type ListView}">
    <Grid Visibility="{Binding IsLoading, Converter={StaticResource myBoolToVisibilityConverter}}">
        <local:ActivityIndicatorControl 
            HorizontalAlignment="Center" 
            Height="Auto" 
            Margin="0" 
            VerticalAlignment="Center"/>
    </Grid>
</ControlTemplate>

Answer 2

Use .NET's built in Converter

.NET 3 has a built in BooleanToVisibilityConverter .

(Note: May not be available on all platforms, ex: mobile)

First add it to your Resources

<UserControl.Resources>
    <BooleanToVisibilityConverter x:Key="bool2vis"></BooleanToVisibilityConverter>
</UserControl.Resources>

Then use it on an element

<Label Visibility="{Binding IsSomeProperty, Converter={StaticResource bool2vis}}" />

Inverting

How do I invert BooleanToVisibilityConverter?

If you want to invert the converter (ex: hide the element when your property is true), this answer has a custom implementation of IValueConverter that supports that via XAML

<Application.Resources>
    <app:BooleanToVisibilityConverter 
        x:Key="BooleanToVisibilityConverter" 
        True="Collapsed" 
        False="Visible" />
</Application.Resources>