Embedded Forms as reusable Frames

fpGUI allows you to embed a Form inside another Form. This is similar to the Delphi-like TFrame idea. This is very handy if you want to reuse a UI design in multiple places in your application.

At first you will be tempted to design a "frame" using a TfpgForm descendant, because that is what the UI Designer will create for you by default. Please refrain from using TfpgForm descendants as "frames" because there are quite a few pitfalls. Instead, use TfpgFrame as the base class for a UI Frame design. This eliminates all the possible problems you might get. You can still use the UI Designer because, the UI Designer simply ignores the base class of any UI design - it only care about what is inside the designer comment markers.

What are the problems when you descend from TfpgForm

• Drag-n-Drop under X11 will stop working for those forms. The XDND protocol needs to speak to the top-level form. When you use a TfpgForm as an embedded form or frame, it will find the wrong TfpgForm, and DND will simply not work.
• You could display an embedded form as modal, meaning it will block all other input to the application, making the outer parent form look like it is frozen.
• A TfpgForm has a WindowPosition property which is by default set to wpAuto. This means, fpGUI leaves it up to the OS or Window Manager to decide where that form mast first appear. This also means that your Top/Left position you specify for the embedded form will most likely be ignored - giving undesired results.

Simply using TfpgFrame as your base class for embedded forms/frames will resolve all these issues for you. For an example of this, take a look at the demo project in [fpgui]/examples/embedded_form/ directory.