---
title: "outlineView(_:mouseDownInHeaderOf:)"
framework: appkit
role: symbol
role_heading: Instance Method
path: "appkit/nsoutlineviewdelegate/outlineview(_:mousedowninheaderof:)"
---

# outlineView(_:mouseDownInHeaderOf:)

Sent to the delegate whenever the mouse button is clicked in outlineView while the cursor is in a column header tableColumn.

## Declaration

```swift
@MainActor optional func outlineView(_ outlineView: NSOutlineView, mouseDownInHeaderOf tableColumn: NSTableColumn)
```

## Parameters

- `outlineView`: The outline view that sent the message.
- `tableColumn`: The table column.

## See Also

### Working with Table Columns

- [outlineView(_:didClick:)](appkit/nsoutlineviewdelegate/outlineview(_:didclick:).md)
- [outlineView(_:didDrag:)](appkit/nsoutlineviewdelegate/outlineview(_:diddrag:).md)