Event Handlers

For normal EA panels, use the Event Bus: MuiEventSink, .Id(...), and OnMuiEvent(...).

This page is for advanced ModernUI handler APIs that still exist for compatibility, reusable controls, and specialised behaviour.

When to use the event bus

Use the event bus when an EA needs to react to common user actions:

button clicks
checkbox changes
spin edit changes
slider changes
confirm dialog results
drawer open/close state

m_bSave=Mui::ButtonPrimary(parent,"Save");
m_bSave.Id(APP_ACTION_SAVE);

When to use low-level handlers

Use handler classes when you are building advanced library-style code, custom reusable controls, or using an API that specifically requires a handler object.

Examples include some legacy button paths, combo paths, tabs, accordions, table/list/tree intent callbacks, date/color callbacks, and custom reusable components.

Ownership rule

The most important rule is ownership:

Some APIs own and delete the handler pointer.
Some APIs store a non-owning pointer.

Check the control or wrapper docs before deciding whether to pass new HandlerClass() or a static/global handler instance.

Button click handler

Buttons can still use MuiClickHandler directly.

class SaveHandler : public MuiClickHandler
{
public:
  virtual void OnChanged(MuiRoot &root,MuiEvent &e)
  {
    Mui::ToastSuccess(root,"Saved");
  }
};

Attach to a button:

MuiButtonAction *save=Mui::Button(parent,"Save",new SaveHandler(),160.0,0.0);

Or after creation:

if(button!=NULL)
  button.SetHandler(new SaveHandler());

MuiButtonAction owns handlers assigned through its owned handler path. Use new for that path.

Owned vs non-owned examples

Area	Typical ownership
Button `SetHandler`	Owned
`ButtonRow` button handlers	Owned through the button
`ButtonGroup` internal pick handlers	Owned by the buttons
List/table/tree selection intent handlers	Not owned
`MuiTabs::SetHandler(MuiTabChangedHandler*)`	Owned
`MuiTabs::SetTabChangedHandler(...)`	Not owned
`MuiComboBoxHost::SetSelectionChangedHandler`	Not owned
`MuiDialog::SetResultHandler`	Not owned
`MuiDrawer::SetStateChangedHandler`	Not owned

Safe patterns

For owned handler APIs:

button.SetHandler(new SaveHandler());

For non-owned handler APIs:

static MySelectionHandler s_handler;
table.SetSelectionChangedHandler(&s_handler);

Avoid this for owned APIs:

SaveHandler handler;
button.SetHandler(&handler);

The pointer may be deleted by the control, or may outlive the stack object.