Ability to paint Custom Controls & Embed Forms
We'd like the ability to define a custom control by painting it (which could be made of up of other custom controls) and/or the ability to embed a form within another as if it's a control.
We've got various custom controls implemented for different purposes in our system, which are built dynamically at runtime. These are time consuming to implement, as all the code has to be written to correctly position/style child controls. We've also had to implement our own way of mapping child control events to parent controls, which again, means more code to be written to tie it altogether .. which gets more complicated when a custom control with events it defines can be used on both a form directly or embedded within another custom control, that have to be invoked/redirected appropriately.
We also implement wizard functionality, which is made up of a range of many different border-less forms, that are set as the child to a parent form which provides the overall wizard navigation. The framework for this is overly complicated as we have to handle moving the child form when the parent is moved, along with handling resize events, which need to calculate whether or not scroll-bars should be shown to adhere to minimum client sizes of the child, as part of which, when showing/removing scrollbars, we have to remove/re-add parent aspect settings on controls .. which can go haywire when child forms need to change those regardless, such that we can no longer rely on resetting things back to the persistent definition from the painter.
While we've been able to tackle most problems (albeit with screen flickering and delays in child forms being moved/resized on thin clients when the app server is busy), there are things we've simply not been able to achieve in a practical way. In particular, tabbing through controls on parent and child in the correct order backwards/forwards and accelerator keys (which only work when the specific form has focus). For the latter, we've set a guideline for other developers that they just shouldn't use & in button captions in case they won't work depending on what's got focus.