ContentSizeFitter.cs

using UnityEngine.EventSystems;

namespace UnityEngine.UI
{

[AddComponentMenu("Layout/Content Size Fitter", 141)]	
[ExecuteInEditMode]
[RequireComponent (typeof (RectTransform))]
public class ContentSizeFitter : UIBehaviour, ILayoutSelfController
{
	public enum FitMode
	{
		Unconstrained,
		MinSize,
		PreferredSize
	}
	
	[SerializeField] protected FitMode m_HorizontalFit = FitMode.Unconstrained;
	public FitMode horizontalFit { get { return m_HorizontalFit; } set { SetPropertyUtility.SetStruct (ref m_HorizontalFit, value, SetDirty); } }
	
	[SerializeField] protected FitMode m_VerticalFit = FitMode.Unconstrained;
	public FitMode verticalFit { get { return m_VerticalFit; } set { SetPropertyUtility.SetStruct (ref m_VerticalFit, value,SetDirty); } }
	
	[System.NonSerialized] private RectTransform m_Rect;
	private RectTransform rectTransform
	{
		get
		{
			if (m_Rect == null)
				m_Rect = GetComponent<RectTransform> ();
			return m_Rect;
		}
	}
	
	private DrivenRectTransformTracker m_Tracker;

	protected ContentSizeFitter()
	{}

	#region Unity Lifetime calls

	protected override void OnEnable ()
	{
		SetDirty ();
	}

	protected override void OnDisable()
	{
		m_Tracker.Clear ();
	}
	#endregion

	private void HandleSelfFittingAlongAxis (int axis)
	{
		FitMode fitting = (axis == 0 ? horizontalFit : verticalFit);
		if (fitting == FitMode.Unconstrained)
			return;
		
		m_Tracker.Add (this, rectTransform,
			(axis == 0 ? DrivenTransformProperties.AnchorMaxX : DrivenTransformProperties.AnchorMaxY) |
			(axis == 0 ? DrivenTransformProperties.SizeDeltaX : DrivenTransformProperties.SizeDeltaY));
		
		// Set anchor max to same as anchor min along axis
		Vector2 anchorMax = rectTransform.anchorMax;
		anchorMax[axis] = rectTransform.anchorMin[axis];
		rectTransform.anchorMax = anchorMax;
		
		// Set size to min size
		Vector2 sizeDelta = rectTransform.sizeDelta;
		if (fitting == FitMode.MinSize)
			sizeDelta[axis] = LayoutUtility.GetMinSize (m_Rect, axis);
		else
			sizeDelta[axis] = LayoutUtility.GetPreferredSize (m_Rect, axis);
		rectTransform.sizeDelta = sizeDelta;
	}
	
	public void SetLayoutHorizontal ()
	{
		m_Tracker.Clear ();
		HandleSelfFittingAlongAxis (0);
	}
	
	public void SetLayoutVertical ()
	{
		HandleSelfFittingAlongAxis (1);
	}
	
	protected void SetDirty ()
	{
		if (!IsActive ())
			return;

		LayoutRebuilder.MarkLayoutForRebuild (rectTransform);
	}
	
	#if UNITY_EDITOR
	protected override void OnValidate ()
	{
		SetDirty ();
	}
	#endif
}

}