go to the reference source<\/a>, you’ll see how the BCL decides whether a window is the main window:<\/p>\nbool IsMainWindow(IntPtr handle)\r\n{\r\n if (NativeMethods.GetWindow(new HandleRef(this, handle),\r\n NativeMethods.GW_OWNER) != (IntPtr)0 ||\r\n !NativeMethods.IsWindowVisible(new Handleref(this, handle)))\r\n return false;\r\n\r\n return true;\r\n}\r\n<\/pre>\nAccording to the BCL heuristics, any unowned visible window is a candidate for being the “main” window.<\/p>\n
Since the Contoso program hid all of its windows, there are no “main” windows as far as the Main\u00adWindow\u00adHandle<\/code> property is concerned. The process.Main\u00adWindow\u00adHandle<\/code> property is null<\/code>, and naturally that means that the code doesn’t actually do anything with the main window of the previous instance.<\/p>\nYou need to move away from the heuristic-based window-detection and design something more deterministic. Here are some ideas.<\/p>\n
\n- Give the main window a unique class name like
Contoso_Main\u00adWindow<\/code>. Enumerate the top-level windows owned by the previous instance and look for one that has the correct class name. (This solution won’t work for this particular customer because the class name for Windows Forms windows cannot be customized.)<\/li>\n- Register a custom message like
Is\u00adContoso\u00adMain\u00adWindow<\/code>. Have your main window respond TRUE<\/code> to that message, and have the second instance send this message to each candidate, and see which one returns TRUE<\/code>.<\/li>\n- Create a named shared memory block and put the window handle in it.<\/li>\n
- Find some other shared data storage that you can use to hold the window handle.<\/li>\n<\/ul>\n
This list is far from exhaustive, but gives you an idea of the sort of thinking you need to engage in.<\/p>\n","protected":false},"excerpt":{"rendered":"
If you really need to find your main window, you’ll have to come up with something more determinstic.<\/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-106192","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
If you really need to find your main window, you’ll have to come up with something more determinstic.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/106192","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=106192"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/106192\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=106192"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=106192"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=106192"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}