MVVM 绑定在设计时不起作用

Question

I tried to bind the visibility of a few buttons to some booleans in a viewmodel and make it work in design-time. I did this several times and never had a problem, but now it does not work and I don't have a clue why. Note that everything works fine when I run the application.

I extracted the essence into a separate app and it still doesn't work!

My XAML:

<Window x:Class="BindingTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:bindingTest="clr-namespace:BindingTest"
        Title="MainWindow" Height="350" Width="525"
        mc:Ignorable="d"
        d:DataContext="{d:DesignInstance bindingTest:TestViewModel, d:IsDesignTimeCreatable=true}">
    <Grid>
        <Grid.Resources>
            <BooleanToVisibilityConverter x:Key="BoolToVis"/>
        </Grid.Resources>
        <StackPanel>
            <Button Visibility="{Binding IsButton1Visible, Converter={StaticResource BoolToVis}}">Hallo 1</Button>
            <Button Visibility="{Binding Button2Visibility}">Hallo 2</Button>
            <Button>Hallo 3</Button>
        </StackPanel>
    </Grid>
</Window>

My ViewModel:

public class TestViewModel
{
    public bool IsButton1Visible
    {
        get { return true; }
    }

    public Visibility Button2Visibility
    {
        get { return Visibility.Hidden; }
    }
}

To make it work in the real app, i added to the constructor of the XAML:

DataContext = new TestViewModel();

This is all pretty simple, but why is it not working in the designer?? I always got this to work in the past and now I tried for hours... It's not the only binding not working, but why is not even this working??

Expected Result:

• Button1 visible
• Button2 hidden
• Button3 visible

Result in the designer:

• Button1 collapsed
• Button2 visible
• Button3 visible

Answer 1

UPDATE: The problem with design-time DataContext bindings not working is due to mistakenly using the d: namespace prefix for the IsDesignTimeCreatable property.

So, change

d:IsDesignTimeCreatable=True

to

IsDesignTimeCreatable=True

and everything should be fine. (My bug report filed with MS will be updated with this information as well.)

---

As this problem with the design-time DataContext bindings not working was consistently reproducable in VS2015 as well as VS2013 when IsDesignTimeCreatable is prefixed with the d: namespace (see comments below the question), i decided to file a bug report with Microsoft: Issue #1651633 "WPF designer: Designtime DataContext bindings broken?" .

Lets see how Microsofts will follow-up with regard to this issue. It should be addressed, since such an issue can catch a developer off-guard and make him reinstall Visual Studio for no benefit... ;)

Answer 2

If anything is OK with the code, there could be an other tricky problem:

In the Designer of Visual Studio a new button was introduced in 2019, which enables / disables the preview of design data .

It's a very tiny button on botton left of the designer window. It's tooltip is "Enable Project Code".

Click this important toggle button to see the design data. (But be aware that you don't disable it, if it's already enabled.)