gistfile1.cs

[SerializeField] private TextAsset xmlAsset;

public SpriteAlignment spriteAlignment = SpriteAlignment.Center;

public Vector2 customOffset = new Vector2(0.5f, 0.5f);

public void OnGUI() {
        xmlAsset = EditorGUILayout.ObjectField("XML Source", xmlAsset, typeof (TextAsset), false) as TextAsset;

        spriteAlignment = (SpriteAlignment) EditorGUILayout.EnumPopup("Pivot", spriteAlignment);

        bool enabled = GUI.enabled;
        if (spriteAlignment != SpriteAlignment.Custom) {
            GUI.enabled = false;
        }

        EditorGUILayout.Vector2Field("Custom Offset", customOffset);

        GUI.enabled = enabled;

        if (xmlAsset == null) {
            GUI.enabled = false;
        }

        if (GUILayout.Button("Slice")) {
            //PerformSlice();
        }

        GUI.enabled = enabled;
    }