intended to receive only messages sent or posted directly to them<\/a>. You use them when you want to use the message queue as a communication channel rather than for hosting UI.<\/p>\nSo don’t host UI on a message-only window. That’s not what it’s for. If you want the dialog box to be independent of other top-level windows, you can use NULL<\/code> as the owner, in which case it appears on the taskbar and in the Alt<\/kbd>+Tab<\/kbd> list. If you want to hide the dialog from the taskbar and the Alt<\/kbd>+Tab<\/kbd> list, then create your own hidden window (not message-only) and use that hidden window as the owner.\u00b9<\/p>\nBonus chatter<\/b>: If you use HWND_MESSAGE<\/code> as the owner window for functions like Dialog\u00adBox<\/code> or Message\u00adBox<\/code>, you’d think, “Oh, well, the dialog box will just become one big message-only window. The user can’t see it, but I can still manipulate it programmatically.” And then you find that, no, the Dialog\u00adBox<\/code> and Message\u00adBox<\/code> functions simply fail when given HWND_MESSAGE<\/code> as an owner. That’s because those functions, as part of their parameter validation, do an IsWindow(hwndOwner)<\/code>, and IsWindow(HWND_MESSAGE)<\/code> is FALSE<\/code> because and HWND_MESSAGE<\/code> is not a real window; it’s a sentinel value for Create\u00adWindow<\/code> and Find\u00adWindow\u00adEx<\/code>. As far as Dialog\u00adBox<\/code> and Message\u00adBox<\/code> are concerned, HWND_MESSAGE<\/code> is an invalid window, so passing it as hwndOwner<\/code> fails with “invalid parameter”.<\/p>\nBonus bonus chatter<\/b>: Sometimes we see programs that build an entire universe inside a message-only window, and then use the Set\u00adParent<\/code> trick to convert the message-only window into a non-message-only window, as if to say, “Ta-da! Here I am!” Please don’t do that. Building your universe probably involves sending internal messages (for example, child windows may send WM_PARENT\u00adNOTIFY<\/code> messages to their parent), which is sort of what message-only windows don’t<\/i> want. “Don’t bother me with your own weird messages. I care only about my own messages.” Just keep your top-level window hidden and then show it when you’re ready.<\/p>\n\u00b9 For keyboard accessibility, your options are either to put the dialog box in the Alt<\/kbd>+Tab<\/kbd> list, or to hide it from the Alt<\/kbd>+Tab<\/kbd> list but provide some other keyboard mechanism to get focus back to that dialog box. For example, you might say, “Go back to whatever you did to trigger the dialog box in the first place, and trigger it again.” This alternate solution is the mechanism that Windows 95’s Explorer used to put keyboard focus back onto a property sheet: Go back to the original thing and ask for Properties again. (Today, Explorer just puts the property sheet in the Alt<\/kbd>+Tab<\/kbd> list.)<\/p>\n","protected":false},"excerpt":{"rendered":"If you want to host UI, use a real window (possibly hidden).<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-111817","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
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