I often meet an error called "REGDB_E_CLASSNOTREG Class not registered"

[cjw1115]

this is my model IDL

namespace BlankApp1
{
    runtimeclass  Model : Windows.UI.Xaml.DependencyObject, Windows.UI.Xaml.Data.INotifyPropertyChanged
    {
        Model();
        String Title;
    }
}

---

Document Details

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• ID: a4db0aab-b906-9dec-381c-ceccc1e90c45
• Version Independent ID: 493a4c50-ffa1-5e32-c757-92306c952887
• Content: XAML controls; bind to a C++/WinRT property - UWP app developer
• Content Source: windows-apps-src/cpp-and-winrt-apis/binding-property.md
• Product: windows
• GitHub Login: Steven White (@stevewhims)
• Microsoft Alias: stwhi

[stevewhims]

Hi, CQ (@cjw1115), that error can happen if you instantiate a locally-implemented runtime class via the projected type's default constructor. For example, if you declare a field like this:

private:
    BlankApp1::Model m_model; // This attempts to call the projected type's default constructor, which won't work if you've declared BlankApp1::Model in the same project, because that type is not registered.

Instead, do this:

private:
    BlankApp1::Model m_model{ nullptr }; // This calls a special constructor on the projected type, which doesn't attempt to activate the runtime class (hence it needn't be registered).

And then assign a value to that field later like this:

m_model = winrt::make<BlankApp1::implementation::Model>(); // BlankApp1::implementation::Model is the implementation type, but winrt::make returns the projected type. Again, this succeeds without the type needing to be registered.

The topic in question shows this same pattern. And the Troubleshooting topic indicates other reasons you might be seeing REGDB_E_CLASSNOTREGISTERED.

[cjw1115]

It works well after I correct my code as you described. Thanks a lot~

[stevewhims]

Great! Thanks, CQ (@cjw1115). ~Steve