Handlers

A handler attribute names a method on your view. The value must be a plain C# identifier (AUI109 if it is not), and the method is scaffolded into Name.cs for you the first time.

<button onclick="Buy" key="shop.buy"/>

public void Buy() { }

Every signature

Attribute	On	Signature
onclick	button	void Name()
onhover, onleave, onpress, onrelease	button, toggle	void Name()
onchange	toggle	void Name(bool value)
onchange	slider	void Name(float value)
onchange	select	void Name(int index)
onchange	tabs, pages	void Name(int page)
onsubmit	input	void Name(string value)
onsubmit	input type="url"	void Name(VRCUrl value)
onselect	repeat	void Name(int row)
onopen, onclose	modal	void Name()
on-<event>	a nested view	matches the child's <event type>

Inside a <repeat> or <template>, the row comes first:

Where	Signature
onclick on a button in a repeat	void Name(int row)
onchange on a toggle in a repeat	void Name(int row, bool value)
onchange on a slider in a repeat	void Name(int row, float value)

The value is always the new value, and the bound property has already been updated when your handler runs.

Pointer events

onhover, onleave, onpress and onrelease fire on any clickable. They are for behaviour, not appearance: hover and pressed looks belong in the stylesheet as :hover and :pressed rules, which cost nothing at runtime.

<button onclick="Pick" onhover="Preview" onleave="Unpreview" key="shop.pick"/>

public void Preview()   { if (preview != null) preview.Show(); }
public void Unpreview() { if (preview != null) preview.Hide(); }

Handlers and bindings together

A control that is both bound and handled writes the binding first, then calls you:

<toggle bind="{mute}" key="audio.mute" onchange="MuteChanged"/>

public void MuteChanged(bool value)
{
    // Mute == value already
    if (audio != null) audio.SetMuted(value);
}

So a handler does not need to store the value; read the property whenever you need it.

Handlers you did not write

If a handler named in markup has no matching method, the build stops with AUI502 and the console line points at the view. The fix is to add the method with the right signature; the VS Code extension offers a quick fix that writes the stub into your .cs.

If you rename a handler in the markup, the old method stays in your .cs (nothing deletes your code) and a new empty one is scaffolded. Move your body across and delete the old one.

A wrong signature blocks the whole queue

The build queue only runs when the project compiles. A handler with the wrong signature is a compile error, so saving more .aui files appears to do nothing. Fix the C# error first, then save the view again or run AUI/Rebuild All Views.

Events from nested views

A child view raises an event; the parent handles it with on-<event>:

<PlayerCard nick="{name}" score="{pts}" on-kicked="PlayerKicked"/>

// in PlayerCard.cs
public void Kick() { EmitInt("kicked", Score); }

// in the parent
public void PlayerKicked(int score) { }

The payload type comes from the child's <event name="kicked" type="int"/> declaration. See components.

Next

• Bindings for the values handlers work with.
• Lists for row handlers.
• Components for parent and child views.