GetColorValue<\/em>, is in IUISettings3 – and it’s the only function in that interface! This makes translation trivial, and we now have all the definitions we need.<\/p>\n\n\n\ntype\n IUISettings3 = interface (IInspectable)\n ['{03021BE4-5254-4781-8194-5168F7D06D7B}']\n function GetColorValue (desiredColor: TUIColorType; out Value: UINT32): HRESULT; stdcall;\n end;\n<\/pre>\n\n\n\n2. Figure out what that HStringReference wrapper does<\/h3>\n\n\n\n
Well, obviously it’s a wrapper for an HSTRING. What’s an HSTRING? It’s how the Windows Runtime manages strings (because there weren’t enough string types already). For FPC’s purposes, they’re equivalent to Handles. The function we need to call in step 3, ActivateInstance()<\/em>, takes an HSTRING as it’s first parameter.<\/p>\n\n\n\nIt turns out we can manipulate HSTRINGs using the WindowsCreateString()<\/em> and WindowsDeleteString()<\/em> functions in the Windows Runtime. Of course, FPC has no idea about HSTRINGs or about the Windows Runtime in general. Additionally, we don’t want to make our program dependent on the Windows Runtime (Windows 8+) unnecessarily – not being able to acquire the user’s accent color is a really poor reason to prevent an application from executing on earlier Windows versions. So we need to use dynamic linking. The key code you need to dynamically link against the Windows Runtime (for our purposes) is as follows:<\/p>\n\n\n\nconst\n WINRTSTRING_DLL = 'api-ms-win-core-winrt-string-l1-1-0.dll';\ntype\n TWindowsCreateString = function (sourceString: PCNZWCH; Length: UINT32; out Str: HSTRING): HRESULT; stdcall;\n TWindowsDeleteString = function (Str: HSTRING): HRESULT; stdcall;\n<\/pre>\n\n\n\nFor space, I’ll leave out the usual calls to LoadLibrary <\/em>and GetProcAddress<\/em>; they’re included in the full downloadable source code at the end of this article. Now we have some functions we can use to obtain HSTRINGs from PWideChar strings (which are FPC-native), what do we actually populate the HSTRING with? What’s this – RuntimeClass_Windows_UI_ViewManagement_UISettings<\/em> ?<\/p>\n\n\n\nOK, that one’s easy. It’s just a constant string:<\/p>\n\n\n
\nconst\nRunTimeClass_UISettings = WideString('Windows.UI.ViewManagement.UISettings')\n<\/pre>\n\n\n\n3. Call a function called ActivateInstance()<\/h3>\n\n\n\n
Getting closer to the action… now we’ve got the HSTRING, and we’ve got the interfaces we want to populate. But what is this wf::ActivateInstance()<\/em> call?<\/p>\n\n\n\nThis function is defined in the Windows Runtime too, and it’s how we actually instantiate the UISettings interface. But before we do so, and similarly to how normal COM works, we need to initialize (and eventually uninitialize) the runtime itself before we can instantiate interfaces from it. As before, here are the types you need for dynamic linking:<\/p>\n\n\n
\nconst\n WINRTCORE_DLL = 'api-ms-win-core-winrt-l1-1-0.dll';\ntype\n TRoInitialize = function (InitType: RO_INIT_TYPE): HRESULT; stdcall;\n TRoUninitialize = procedure; stdcall;\n TRoActivateInstance = function (activatableClassId: HSTRING; out Instance: IInspectable): HRESULT; stdcall;\n<\/pre>\n\n\n\nAnd finally, here is how we put it all together to finally obtain a usable IUISettings3 interface instance:<\/p>\n\n\n
\n\/\/ ALL ERROR checking omitted - refer to source code at end of article!\nvar\n Hstr : HSTRING;\n Inspectable : IInspectable;\n UISettings : IUISettings3;\nbegin\n RoInitialize(RO_INIT_MULTITHREADED);\n WindowsCreateString(RunTimeClass_UISettings\n ,Length(RunTimeClass_UISettings),hstr);\n RoActivateInstance(hstr,Inspectable);\n UISettings := Inspectable as IUISettings3;\n \/\/ ..use our UISettings object!\n UISettings := nil;\n Inspectable := nil;\n WindowsDeleteString(hstr);\n RoUninitialize; \/\/ more on this below\nend;\n<\/pre>\n\n\n\n4. Call UISettings.GetColorValue() to obtain colour<\/h3>\n\n\n\n
After all the setup work to get to this point, this part is trivially easy:<\/p>\n\n\n
\nvar\n color : dword;\nbegin\n UISettings.GetColorValue(Accent,color);\nend;\n<\/pre>\n\n\n\nAccent is the TUIColorType<\/em> enum we defined earlier; if you’re lazy, you can replace this with the magic integer 5. Color is the same type as Windows’ GDI Color: a dword, in BRGA format. <\/p>\n\n\n\n5. Tidying up<\/h3>\n\n\n\n
If you’ve been following along, you should be able to build a working sample from the above code, but if you run it, it won’t be quite perfect. It’ll work, and you’ll get an actual color value, BUT your program will exception out with an Access Violation when your IUISettings interface variable leaves scope.<\/p>\n\n\n\n
This is an unfortunate consequence of FPC not having a native understanding of the types we’re working with; even though we explicitly set UISettings<\/em> and Inspectable<\/em> to nil, the compiler still believes we’re holding a reference, and finalizes it when the variables leave scope. Unfortunately, if that’s *after* we’ve called RoUninitialize<\/em>, we’ll take an access violation. I’ve tried various methods to try and figure out where FPC thinks the extra reference is, or alternatively to try and tell it *not* to be smart about finalization, but I’ve only found three methods that work reliably:<\/p>\n\n\n\n- Just don’t call RoUninitialize<\/li>
- Make sure the variable’s scope ends before calling RoUninitialize<\/li>
- Move RoInitialize and RoUninitialize to unit initialization\/finalization seconds<\/li><\/ol>\n\n\n\n
Of the three, the second is my preferred option – and the way you’ll find it laid out in the attached source code. FPC doesn’t quite have the fine-grained scope control of C++, but you can simply wrap a nested procedure or function to do the same job. In pseudocode:<\/p>\n\n\n
\nbegin\n RoInitialize(RO_INIT_MULTITHREADED);\n DoActualWork;\n RoUninitialize;\nend.\n\nprocedure DoActualWork;\nvar\n UISettings: IUISettings3;\nbegin\n \/\/ ... etc\nend;\n<\/pre>\n\n\n\nOption 3 (using an FPC Unit’s initialization\/finalization sections) works just fine too – and I’d probably use that if I was going to statically link to the WinRT DLLs; but with Dynamic Linking, I chose to keep everything self-contained within a function instead.<\/p>\n\n\n\n
Side note: If you have a smarter way of trying to prevent FPC from generating the spurious finalization call, I’d love to hear it!<\/p>\n\n\n\n
Source Code and demo<\/h3>\n\n\n\n
Because I couldn’t find an FPC version of this code anywhere else on the internet, I’ve made the smallest possible working code sample available too (tested with FPC 3.0.4). Here’s the source code and a compiled demo download<\/a>. (18.6KB).<\/p>\n","protected":false},"excerpt":{"rendered":"I’m currently designing a minimalistic user interface in FPC (Freepascal), and I wanted it to blend in with the existing Windows desktop. So naturally, I started looking for how to obtain the user’s chosen accent color (I’m deliberately alternating American and British spelling of colour\/color to help anyone that needs this to be able to<\/p>\n","protected":false},"author":2722,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,18],"tags":[83,35,4,21,80],"class_list":["post-555","post","type-post","status-publish","format-standard","hentry","category-code","category-good-coding-guidelines","tag-accent","tag-fpc","tag-freepascal","tag-ui","tag-windows-runtime"],"_links":{"self":[{"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/posts\/555","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/users\/2722"}],"replies":[{"embeddable":true,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/comments?post=555"}],"version-history":[{"count":32,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/posts\/555\/revisions"}],"predecessor-version":[{"id":730,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/posts\/555\/revisions\/730"}],"wp:attachment":[{"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/media?parent=555"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/categories?post=555"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.paradicesoftware.com\/blog\/wp-json\/wp\/v2\/tags?post=555"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}