comctl32/listview: Header should be created when LVS_EX_HEADERDRAGDROP set.

dlls/comctl32/listview.c

@@ -7268,7 +7268,12 @@ static DWORD LISTVIEW_SetExtendedListViewStyle(LISTVIEW_INFO *infoPtr, DWORD dwM
     
     if((infoPtr->dwLvExStyle ^ dwOldExStyle) & LVS_EX_HEADERDRAGDROP)
     {
-        DWORD dwStyle = GetWindowLongW(infoPtr->hwndHeader, GWL_STYLE);
+        DWORD dwStyle;
+
+        /* if not already created */
+        LISTVIEW_CreateHeader(infoPtr);
+
+        dwStyle = GetWindowLongW(infoPtr->hwndHeader, GWL_STYLE);
         if (infoPtr->dwLvExStyle & LVS_EX_HEADERDRAGDROP)
             dwStyle |= HDS_DRAGDROP;
         else

dlls/comctl32/tests/listview.c

@@ -965,6 +965,17 @@ static void test_create(void)
     /* HDS_DRAGDROP set by default */
     ok(GetWindowLongPtr(hHeader, GWL_STYLE) & HDS_DRAGDROP, "Expected header to have HDS_DRAGDROP\n");
     DestroyWindow(hList);
+
+    /* setting LVS_EX_HEADERDRAGDROP creates header */
+    hList = CreateWindow("SysListView32", "Test", LVS_REPORT, 0, 0, 100, 100, NULL, NULL,
+                          GetModuleHandle(NULL), 0);
+    ok(!IsWindow(hHeader), "Header shouldn't be created\n");
+    ok(NULL == GetDlgItem(hList, 0), "NULL dialog item expected\n");
+    SendMessage(hList, LVM_SETEXTENDEDLISTVIEWSTYLE, 0, LVS_EX_HEADERDRAGDROP);
+    hHeader = (HWND)SendMessage(hList, LVM_GETHEADER, 0, 0);
+    ok(IsWindow(hHeader), "Header should be created\n");
+    ok(hHeader == GetDlgItem(hList, 0), "Expected header as dialog item\n");
+    DestroyWindow(hList);
 }
 
 static void test_redraw(void)