求助：WPF中因未知DataContext无法解析符号DemoItems

I’ve run into this exact ReSharper/WPF issue multiple times, so I know how frustrating those false positive errors can be. The core problem here is that ReSharper can’t figure out what DataContext your XAML is using, so it can’t locate the DemoItems property from your MainWindowViewModel. Since you’ve already fixed a similar "MyVariable" error, you can reuse some of that logic—here’s how to apply it to this case:

1. Add a design-time DataContext to your XAML #

This is the go-to fix for these ReSharper errors, and it’s probably what you used before. It tells ReSharper exactly what ViewModel type to expect at design time.

First, make sure you have the design-time and local namespaces declared at the top of your XAML file:

xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:YourProjectNamespace.ViewModels" <!-- Swap in your actual ViewModel namespace -->

Then add the d:DataContext attribute to your root Window or UserControl element:

<Window x:Class="YourProject.MainWindow"
        ...
        d:DataContext="{d:DesignInstance Type=local:MainWindowViewModel, IsDesignTimeCreatable=True}">

• If your MainWindowViewModel has dependencies that can’t be resolved at design time (like your ISnackbarMessageQueue), set IsDesignTimeCreatable=False—ReSharper will still recognize the property types without instantiating the ViewModel.

2. Confirm your runtime DataContext is set correctly #

ReSharper sometimes uses runtime binding clues to validate properties. Double-check that your MainWindow is assigning the DataContext properly:
In MainWindow.xaml.cs:

public MainWindow()
{
    InitializeComponent();
    // If you're not using DI, instantiate your ViewModel directly
    DataContext = new MainWindowViewModel(new SnackbarMessageQueue());
    // If using DI, make sure your container injects the ViewModel here
}

3. Clear ReSharper’s cache (for stubborn cases) #

Occasionally, ReSharper’s cache gets corrupted and throws false errors. Here’s how to fix that:

• Open the ReSharper menu → Options (or hit Alt+R, O)
• Go to Environment → General
• Click Clear Caches and restart Visual Studio.

4. Double-check property details #

Quick sanity check:

• Ensure DemoItems is a public property in your MainWindowViewModel (your code snippet shows this, but it’s easy to miss a modifier)
• Make sure the spelling and capitalization in your XAML match exactly (WPF bindings are case-sensitive—demoItems won’t find DemoItems)

Since you’ve tackled this kind of error before, the design-time DataContext trick should get rid of the "Cannot resolve symbol 'DemoItems'" message right away.

内容的提问来源于stack exchange，提问作者Black Panther