# How to pass collection type parameter to swift-winrt projected winui API?

**URL:** <https://forums.swift.org/t/how-to-pass-collection-type-parameter-to-swift-winrt-projected-winui-api/84065>\
**Category:** Windows\
**Created:** [January 11, 2026, 3:20am UTC](https://forums.swift.org/t/how-to-pass-collection-type-parameter-to-swift-winrt-projected-winui-api/84065 "2026-01-11T03:20:03Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![rayman-zhao](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/rayman-zhao/32/42676_2.png) [@rayman-zhao](https://forums.swift.org/u/rayman-zhao)\
**Post date:** [January 11, 2026, 3:20am UTC](https://forums.swift.org/t/how-to-pass-collection-type-parameter-to-swift-winrt-projected-winui-api/84065/1 "2026-01-11T03:20:03Z")

</div>

For example, there is ItemsSource property in ItemsControl, declared in C++/WinRT :

```swift
IInspectable ItemsSource();

void ItemsSource(IInspectable value);

//The type of the object that you set the ItemsSource property to must implement one of these interfaces: IVector<IInspectable>, IBindableObservableVector etc.

```

Usually, it can be setup by C++/WinRT vector like:

```swift
control.ItemsSource(winrt::single_threaded_vector<winrt::hstring>(…))

```

Based on The Browser Company’s swift-winrt tools, its projections like:

```swift
public var itemsSource : Any! {

        get { try! _default.get_ItemsSource() }

        set { try! _default.put_ItemsSource(newValue) }

 }

```

But how to pass parameter of collection types into?

```swift
control.itemsSource = Array<String>[...].toVector() // Crash, not working

```

Any help or hint is really appreciated, thank you !

---

<div class="post-metadata">

**Author:** ![rayman-zhao](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/rayman-zhao/32/42676_2.png) [@rayman-zhao](https://forums.swift.org/u/rayman-zhao)\
**Post date:** [January 23, 2026, 8:06am UTC](https://forums.swift.org/t/how-to-pass-collection-type-parameter-to-swift-winrt-projected-winui-api/84065/2 "2026-01-23T08:06:32Z")

</div>

Thanks to Mr.Saleem's "Interoperability: Swift's Super Power" and the old but still vary valuable book "Essential COM" from Mr.Don Box. Finally it works.

 ![image](https://global.discourse-cdn.com/swift/original/3X/e/6/e60b6914dfe73f5527c47ea6f350747fd2e45d1e.png)

In summary：

1. Didn't find any exsiting WinRT object implements both IInspectable and IVector, which is required by ItemsSource API. So that no swift projection class can be used directly;

2. Swift can't build as COM object yet. Hope it can do in future;

3. So need to create the COM object in C/C++, then wrapper with Swift, and set the property.

For example, in C++ :

```swift
::IInspectable * CreateIVector()
{
    auto vec = winrt::single_threaded_vector<winrt::Windows::Foundation::IInspectable>();
    vec.Append(winrt::box_value(L"Test"));
    vec.Append(winrt::box_value(L"Test2"));
    vec.Append(winrt::box_value(L"Test3"));
        
    auto inspectable_vec = vec.as<::IInspectable>();
    auto *raw_inspectable_ptr = inspectable_vec.get();
    raw_inspectable_ptr->AddRef();
    return raw_inspectable_ptr;
}

```

Then in Swift, based on swift-winrt of TBC :

```swift
let (com) = ComPtrs.initialize { abi in
    abi = CreateIVector()
}
let insp = WindowsFoundation.IInspectable(com!)
bread.itemsSource = insp

```

Hope above is useful for other people interested in Swift WinUI.