UXRadioGroup

UXRadioGroup makes several UXRadioButtons mutually exclusive.

#use <UXKit>            // or #import "UXControl.xc"

Overview

UXRadioGroup* g = new UXRadioGroup();
g.add(small);
g.add(medium);
g.add(large);

g.select(medium);
g.selected();            // medium

The whole concept of “one of these” is these three methods.

Grouping is by membership, not by layout

A radio button’s exclusivity does not come from its position on screen, a common parent view, or a shared tag. It comes from being in a group.

The alternatives break in a real window. If grouping were positional, two unrelated sets of radio buttons in the same box would exclude each other. If grouping were by parent, a set split across two columns would stop working.

add sets the button’s group back-pointer, so the relationship is established once, from one side, and both halves know about it.

Selecting is the group’s job

void select(UXRadioButton* chosen)

select walks the members and sets each one’s state: the chosen button on, every other off. That single pass is the exclusivity. No rule is enforced elsewhere, and no invariant is maintained between calls.

This has a consequence:

Setting a button’s state directly bypasses the group

Calling setSelected(true) on a member marks that button without clearing its siblings, so two can be lit at once. The group does not notice, because nothing is watching.

Go through select. Reading a button’s state directly is fine; only writing skips the rule.

UXSegment.selected works the same way: the field is state, and the container applies the policy.

selected() scans

UXRadioButton* selected(void)

It returns the first member that is on, or null when nothing has been chosen yet. A validator can test for that null.

Because it scans rather than caching, it stays accurate after a state has been set directly: it reports what is lit, not what the group last decided.

A group with two lit members returns the first. This is how the bypass above shows up.

Members are held strongly

Array* buttons

The group keeps its buttons alive, and each button holds the group. That is a bounded cycle: both are released together when the window that owns them goes.

If a group outlives its buttons for some other reason, the buttons are not collected while the group holds them.

Topics

add · select · selected

add

void add(UXRadioButton* b)

Join the group, and set the button’s back-pointer to it.

There is no remove. A button belongs to a group for as long as both exist, which matches the lifetime of a radio set.

select

void select(UXRadioButton* chosen)

Turn chosen on and everything else off.

Passing a button that is not a member turns every member off. That clears the group, which is useful when intended and a surprise when not.

selected

UXRadioButton* selected(void)

The lit member, or null.

Conforms to

• Inherits Object

See also

• UXRadioButton: the member
• UXSegmentedControl: the same one-of-many choice as a single control
• UXPopUpButton: one-of-many when there is no room to show them all