Unity-Technologies/UnityCsReference · error · ArgumentOutOfRangeException

Invalid index for columnIndexForTreeFoldouts: {0}. Number of

Error message

Invalid index for columnIndexForTreeFoldouts: {0}. Number of available columns: {1}

What it means

Thrown by the setter of columnIndexForTreeFoldouts when the requested column index is outside the range of available columns ([0, multiColumnHeader.state.columns.Length)). The index must reference a real column so the foldout glyph can be placed within it.

Source

Thrown at Editor/Mono/GUI/TreeView/TreeViewControl/TreeViewControl.cs:199

            set { m_GUI.extraSpaceBeforeIconAndLabel = value; }
        }

        protected float customFoldoutYOffset
        {
            get { return m_GUI.customFoldoutYOffset; }
            set { m_GUI.customFoldoutYOffset = value; }
        }

        protected int columnIndexForTreeFoldouts
        {
            get { return m_GUI.columnIndexForTreeFoldouts; }
            set
            {
                if (multiColumnHeader == null)
                    throw new InvalidOperationException("Setting columnIndexForTreeFoldouts can only be set when using TreeView with a MultiColumnHeader");

                if (value < 0 || value >= multiColumnHeader.state.columns.Length)
                    throw new ArgumentOutOfRangeException("value", string.Format("Invalid index for columnIndexForTreeFoldouts: {0}. Number of available columns: {1}", value, multiColumnHeader.state.columns.Length));

                m_GUI.columnIndexForTreeFoldouts = value;
            }
        }

        protected bool useScrollView
        {
            get { return m_TreeView.useScrollView; }
            set { m_TreeView.useScrollView = value; }
        }

        protected Rect GetCellRectForTreeFoldouts(Rect rowRect)
        {
            if (multiColumnHeader == null)
                throw new InvalidOperationException("GetCellRect can only be called when 'multiColumnHeader' has been set");

            int columnIndex = columnIndexForTreeFoldouts;
            int visibleColumnIndex = multiColumnHeader.GetVisibleColumnIndex(columnIndex);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Clamp the index to the valid range: columnIndexForTreeFoldouts = Mathf.Clamp(value, 0, header.state.columns.Length - 1).
2. Verify the column count before assigning.
3. Use index 0 (the first column) as a safe default for foldout placement.

Example fix

// before
tree.columnIndexForTreeFoldouts = 3; // header only has 2 columns

// after
int max = header.state.columns.Length;
tree.columnIndexForTreeFoldouts = Mathf.Clamp(3, 0, max - 1);

int max = header.state.columns.Length;
int idx = Mathf.Clamp(desiredIndex, 0, max - 1);
tree.columnIndexForTreeFoldouts = idx;

static bool IsValidColumnIndex(int idx, MultiColumnHeader h) => idx >= 0 && idx < h.state.columns.Length;

When it happens

Trigger: Setting columnIndexForTreeFoldouts to a value >= the number of columns defined in MultiColumnHeaderState; setting a negative value; setting an index after reducing the number of columns.

Common situations: Hardcoding an index (e.g. 2) when the header state was later changed to fewer columns; dynamic column removal that invalidates a previously-stored foldout column index.

Related errors

• Setting columnIndexForTreeFoldouts can only be set when usin
• visibleColumns should should not be set to an empty array. A
• GetCellRect can only be called when 'multiColumnHeader' has
• Only call this method if you are using a MultiColumnHeader w
• Input row index: {0} is invalid. Number of rows rects: {1}.

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/03be37d2d376b78e. Report an issue: GitHub.