Absolutely you can, but there's a key detail to wrap your head around first: Windows Runtime (WinRT) APIs aren't called like traditional Win32 functions. They're based on a COM-like ABI (Application Binary Interface), so assembly calls need to work directly with interface pointers, virtual tables, and WinRT's calling conventions. Since you already have assembly <-> C++ interop working, you're halfway there—let's break this down for your StorageFolder.GetFilesAsync() example.

Core Concepts to Know #

WinRT APIs expose themselves as ABI interfaces (e.g., IStorageFolder for Windows::Storage::StorageFolder). Every method you call on a WinRT object is actually a call to a function in the interface's virtual table (vtable). You'll need to:

1. Get a pointer to the WinRT interface instance (either from C++ and pass it to assembly, or create it directly in assembly).
2. Locate the target method in the interface's vtable.
3. Follow the correct calling convention (x86 uses __stdcall; x64 uses Microsoft's x64 calling convention with register-passed parameters).
4. Handle WinRT-specific details like HRESULT return codes and asynchronous operations.

Step-by-Step Example: Calling GetFilesAsync from Assembly #

Let's assume you already have a valid IStorageFolder* pointer (e.g., from ApplicationData::Current->LocalFolder in C++) and want to pass it to an assembly function to call GetFilesAsync().

1. First, Understand the ABI Signature #

From the Windows SDK headers (windows.storage.h), the ABI signature for IStorageFolder::GetFilesAsync is:

HRESULT __stdcall GetFilesAsync(
    ::Windows::Storage::Search::CommonFileQuery query,
    ::Windows::Foundation::IAsyncOperation<::Windows::Foundation::Collections::IVectorView<::Windows::Storage::IStorageFile*>**>** operation
);

• Returns an HRESULT (stored in EAX for x86, RAX for x64).
• Takes two parameters: a query enum value, and an output pointer to receive the async operation object.

2. Assembly Implementation (x64) #

Since most modern UWP projects target x64, here's a MASM example that takes an IStorageFolder* and returns the async operation:

First, declare the function in your C++ code:

extern "C" HRESULT __stdcall CallStorageFolderGetFilesAsync(
    IStorageFolder* folder,
    IAsyncOperation<IVectorView<IStorageFile*>**>*& outOperation
);

Then the assembly code:

.CODE
CallStorageFolderGetFilesAsync PROC
    ; x64 calling convention:
    ; RCX = folder (IStorageFolder* - "this" pointer)
    ; RDX = outOperation (output pointer for the async operation)

    ; Step 1: Get the vtable address from the interface pointer
    MOV RAX, [RCX]          ; RAX = IStorageFolder vtable address
    ; Step 2: Locate GetFilesAsync in the vtable
    ; IStorageFolder's vtable order: QueryInterface, AddRef, Release, GetFilesAsync, ...
    ; Each vtable entry is 8 bytes (x64), so offset is 3 * 8 = 24h
    MOV RAX, [RAX + 24h]    ; RAX = pointer to GetFilesAsync method

    ; Step 3: Set up parameters for the call
    MOV R8, RDX             ; R8 = output pointer (second parameter)
    XOR RDX, RDX            ; RDX = CommonFileQuery_DefaultQuery (0, first parameter)
    ; RCX already holds the "this" pointer (first parameter for interface methods)

    ; Step 4: Call the method
    CALL RAX                ; Invoke GetFilesAsync; HRESULT returned in RAX

    RET
CallStorageFolderGetFilesAsync ENDP
END

3. Handling the Async Operation #

GetFilesAsync returns an IAsyncOperation—to get the actual files, you'll need to:

• Wait for the operation to complete (using RoWaitForSingleObject or the async operation's Completed event).
• Call GetResults() on the operation to retrieve the IVectorView<IStorageFile*> collection.

These steps can also be implemented in assembly, but you'll need to repeat the vtable lookup process for the IAsyncOperation interface methods.

Going Further: Creating WinRT Instances in Assembly #

If you want to avoid passing interface pointers from C++ entirely, you can use WinRT's activation functions like RoGetActivationFactory to create instances (e.g., get ApplicationData to access LocalFolder). This is still part of the WinRT runtime, not traditional Win32/COM, so it fits your requirement of focusing on Windows 10+ APIs.

Key Tips #

• Always check the HRESULT return value in assembly to handle errors (e.g., compare RAX to S_OK).
• Manage interface reference counts manually: call AddRef and Release via the vtable to avoid memory leaks.
• Refer to the Windows SDK headers for exact vtable method order and parameter types—this is non-negotiable for correct assembly calls.

Start small: replicate what you can already do in C++/WinRT in assembly step by step, and validate each part with your XAML UI as you go.

内容的提问来源于stack exchange，提问作者anon