FIX: Fixed exceptions being thrown by OnScreenStick and improved warnings related to missing UGUI dependencies for current implementations.

[ekcoh]

Description

CHANGE: Added warning messages to both OnScreenStick and OnScreenButton Inspector editors that would display a warning message in case on-screen control components are added to a GameObject not part of a valid UI hierarchy.
FIX: ISXB-915 OnScreenStick throws System.Exception if added to a GameObject not part of a UGUI object hierarchy.
FIX: ISXB-916 Entering play-mode with a OnScreenStick attached to a non UI hierarchy Game Object floods console with InvalidCastException.

Changes made

See Description. Changes introduced on OnScreenStick and OnScreenButton repectively to respect the fact that base class OnScreenControl is currently agnostic to UI system while OnScreenStick and OnScreenButton currently only support UGUI (UnityEngine.UI).

Notes

Recommend testing with repro steps from linked tickets.

There is also a UX or potential docs perspective to review in how the changes to warning messaged in UI and Console are affected.

Changes require manual verification.

Checklist

Before review:

• Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • FogBugz ticket attached, example ([case %number%](https://issuetracker.unity3d.com/issues/...)).
  • FogBugz is marked as "Resolved" with next release version correctly set.
• Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

After merge:

• Create forward/backward port if needed. If you are blocked from creating a forward port now please add a task to ISX-1444.

[ekcoh]

[ritamerkl]

Just one minor comment, looks good to me.

[ritamerkl]

Minor: a property would be sufficient (e.g. string warningMessage => $"{GetType()} needs t.....";)

[Pauliusd01]

LGTM. Checked that the warnings are shown correctly/not shown when they're not supposed to and double checked on screen controls functionality on android