How to get an array of structures with a "byte array" from WinRT C ++ to C # in a Windows Store application?

Question

Here I have a C # metro application with a C ++ WinRT component. I need to do something in WinRT, for example, assign a name / path to a photo and get a thumbnail of photos.

First, I write the value structure and extract the struct array function in WinRT C ++, as shown below.

public value struct Item { String^ strName; String^ strPath; }; public ref class CTestWinRT sealed { public: CTestWinRT(); void TestOutStructArray(Platform::WriteOnlyArray<Item>^ intOutArray) { intOutArray->Data[0].strName = ref new String(L"test1.jpg"); intOutArray->Data[0].strPath = ref new String(L"c:\\temp"); intOutArray->Data[1].strName = ref new String(L"test2.jpg"); intOutArray->Data[1].strPath = ref new String(L"c:\\temp"); } }; 

Then I use the TestOutStructArray function in the C # button, as shown below.

  CTestWinRT myNative = new CTestWinRT(); private void btnTestClick(object sender, RoutedEventArgs e) { Item[] items = new Item[2]; myNative.TestOutStructArray(items); } 

The function works fine, and the array of elements can see that the values ​​are correct in the debug window.

Now I want to add an array of bytes to the struct value, as shown below.

 public value struct Item { String^ strName; String^ strPath; uint8 byteThumbnail[8096]; }; 

This will result in a compiler error:

error C3987: 'byteThumbnail': public member signature contains native type 'unsigned char [8096]'

error C3992: 'byteThumbnail': public member signature contains invalid type 'unsigned char [8096]'

I look at MSDN about the value of struct, he said that the value of struct cannot have the class ref or struct as a member, so I think I can not write code as indicated above.

http://msdn.microsoft.com/en-us/library/windows/apps/hh699861.aspx

Does anyone know how to use another way to replace value struct? I need the array to have a "byte array" inside.

Answer 1

The following types can be transmitted via ABI:

• const Platform :: Array ^,
• Platform :: Array ^ *,
• Platform :: WriteOnlyArray,
• return value Platform :: Array ^.

A value struct or class value can contain as fields only fundamental numeric types, enumeration classes, or Platform :: String ^.

Thus, you cannot use the construction of values ​​with arrays. And you cannot use arrays like uint8 [].

You must pass arrays and structures separately or using the ref class.