ButtonGroupMixin

ButtonGroupMixin.lua

local ButtonGroupMixin = CreateFromMixins(CallbackRegistryBaseMixin);

function ButtonGroupMixin:Init()
    CallbackRegistryBaseMixin.OnLoad(self);

    self.buttons = {};
    self.selectedButton = nil;
end

function ButtonGroupMixin:AddButton(button)
    if self.buttons[button] then
        return;
    end

    assert(not self:GetButtonByID(button:GetID()), "Duplicate button ID in group");

    self.buttons[button] = true;
    button:SetScript("OnClick", function() self:SetSelectedButton(button); end);
end

function ButtonGroupMixin:GetButtonByID(id)
    -- Linear search; slow, but are you likely to have many in a group?
    for button in pairs(self.buttons) do
        if button:GetID() == id then
            return button;
        end
    end
end

function ButtonGroupMixin:GetSelectedButton()
    return self.selectedButton;
end

function ButtonGroupMixin:GetSelectedID()
    if not self.selectedButton then
        return nil;
    end

    return self.selectedButton:GetID();
end

function ButtonGroupMixin:SetSelectedButton(button)
    if self.selectedButton == button then
        if self.selectedButton then
            -- Prevents the UI from toggling it off visually when clicked.
            self.selectedButton:SetChecked(true);
        end

        return;
    end

    if self.selectedButton then
        self.selectedButton:SetChecked(false);
    end

    self.selectedButton = button;
    self.selectedButton:SetChecked(true);
    self:TriggerEvent("OnSelectedButtonChanged", self.selectedButton);
    self:TriggerEvent("OnSelectedIDChanged", self.selectedButton:GetID());
end

function ButtonGroupMixin:SetSelectedID(id)
    local button = assert(self:GetButtonByID(id), "No button found with given ID");
    self:SetSelectedButton(button);
end

--
-- Example
--

local frame = CreateFrame("Frame", nil, UIParent, "BasicFrameTemplate");
frame:SetPoint("CENTER");
frame:SetSize(640, 480);

local button1 = CreateFrame("CheckButton", nil, frame, "UIRadioButtonTemplate");
button1:SetID(1);
button1:SetPoint("CENTER");
button1:SetText("Button 1");

local button2 = CreateFrame("CheckButton", nil, frame, "UIRadioButtonTemplate");
button2:SetID(2);
button2:SetPoint("TOP", button1, "BOTTOM");
button2:SetText("Button 2");

local button3 = CreateFrame("CheckButton", nil, frame, "UIRadioButtonTemplate");
button3:SetID(3);
button3:SetPoint("TOP", button2, "BOTTOM");
button3:SetText("Button 3");

local group = CreateAndInitFromMixin(ButtonGroupMixin);
group:RegisterCallback("OnSelectedButtonChanged", function(...) print("OnSelectedButtonChanged", ...) end);
group:RegisterCallback("OnSelectedIDChanged", function(...) print("OnSelectedIDChanged", ...) end);
group:AddButton(button1);
group:AddButton(button2);
group:AddButton(button3);