ToggleGroup的使用

 

使用方法很容易，目的是為了實現在一組Toggle內只能勾選一個

1、建立空的GameObject然後綁上一個ToggleGroup，

2、建立一組Toggle，將所有Toggle的Group屬性指向前面的ToggleGroup，到此完成工作

ToggleGroup內有個AllowSwitchOff選項：

勾選：則可以取消所有的勾選項

不勾選：則一定會存在有一個勾選項

內部原始碼（from uGUI-2018.2）

        private void SetToggleGroup(ToggleGroup newGroup, bool setMemberValue)
        {
            ToggleGroup oldGroup = m_Group;

            // Sometimes IsActive returns false in OnDisable so don't check for it.
            // Rather remove the toggle too often than too little.
            if (m_Group != null)
                m_Group.UnregisterToggle(this);

            // At runtime the group variable should be set but not when calling this method from OnEnable or OnDisable.
            // That's why we use the setMemberValue parameter.
            if (setMemberValue)
                m_Group = newGroup;

            // Only register to the new group if this Toggle is active.
            if (newGroup != null && IsActive())
                newGroup.RegisterToggle(this);

            // If we are in a new group, and this toggle is on, notify group.
            // Note: Don't refer to m_Group here as it's not guaranteed to have been set.
            if (newGroup != null && newGroup != oldGroup && isOn && IsActive())
                newGroup.NotifyToggleOn(this);
        }

在設定Toggle的Group時，會將所有的Toggle註冊到同一個ToggleGroup中,並通知開關方法NotifyToggleOn

        public void NotifyToggleOn(Toggle toggle)
        {
            ValidateToggleIsInGroup(toggle);

            // disable all toggles in the group
            for (var i = 0; i < m_Toggles.Count; i++)
            {
                if (m_Toggles[i] == toggle)
                    continue;

                m_Toggles[i].isOn = false;
            }
        }

當點選其中一個Toggle的時候，會觸發註冊的OnPointerClick，主要是NotifyToggleOn和PlayEffect以及自定義的onValueChanged回撥

        public virtual void OnPointerClick(PointerEventData eventData)
        {
            if (eventData.button != PointerEventData.InputButton.Left)
                return;
            InternalToggle();
        }

        private void InternalToggle()
        {
            if (!IsActive() || !IsInteractable())
                return;

            isOn = !isOn;
        }

        public bool isOn
        {
            get { return m_IsOn; }
            set
            {
                Set(value);
            }
        }

        void Set(bool value)
        {
            Set(value, true);
        }

        void Set(bool value, bool sendCallback)
        {
            if (m_IsOn == value)
                return;

            // if we are in a group and set to true, do group logic
            m_IsOn = value;
            if (m_Group != null && IsActive())
            {
                if (m_IsOn || (!m_Group.AnyTogglesOn() && !m_Group.allowSwitchOff))
                {
                    m_IsOn = true;
                    m_Group.NotifyToggleOn(this);
                }
            }

            // Always send event when toggle is clicked, even if value didn't change
            // due to already active toggle in a toggle group being clicked.
            // Controls like Dropdown rely on this.
            // It's up to the user to ignore a selection being set to the same value it already was, if desired.
            PlayEffect(toggleTransition == ToggleTransition.None);
            if (sendCallback)
            {
                UISystemProfilerApi.AddMarker("Toggle.value", this);
                onValueChanged.Invoke(m_IsOn);
            }
        }

NotifyToggleOn上面已經貼出程式碼了，下面是PlayEffect，其實就是改變了graphic的透明度，做一個Tween動畫

        private void PlayEffect(bool instant)
        {
            if (graphic == null)
                return;

#if UNITY_EDITOR
            if (!Application.isPlaying)
                graphic.canvasRenderer.SetAlpha(m_IsOn ? 1f : 0f);
            else
#endif
            graphic.CrossFadeAlpha(m_IsOn ? 1f : 0f, instant ? 0f : 0.1f, true);
        }