By setting a header function on the box one can dynamically add headers
in front of rows, depending on the contents of the row and its position in the list.
For instance, one could use it to add headers in front of the first item of a
new kind, in a list sorted by the kind.
The update_header can look at the current header widget using ListBox.rowGetHeader
and either update the state of the widget as needed, or set a new one using
ListBox.rowSetHeader. If no header is needed, set the header to NULL.
Note that you may get many calls update_header to this for a particular row when e.g.
changing things that don’t affect the header. In this case it is important for performance
to not blindly replace an existing header with an identical one.
The update_header function will be called for each row after the call, and it will
continue to be called each time a row changes (via ListBox.rowChanged) and when
the row before changes (either by ListBox.rowChanged on the previous row, or when
the previous row becomes a different row). It is also called for all rows when
ListBox.invalidateHeaders is called.
By setting a header function on the box one can dynamically add headers in front of rows, depending on the contents of the row and its position in the list. For instance, one could use it to add headers in front of the first item of a new kind, in a list sorted by the kind.
The update_header can look at the current header widget using ListBox.rowGetHeader and either update the state of the widget as needed, or set a new one using ListBox.rowSetHeader. If no header is needed, set the header to NULL.
Note that you may get many calls update_header to this for a particular row when e.g. changing things that don’t affect the header. In this case it is important for performance to not blindly replace an existing header with an identical one.
The update_header function will be called for each row after the call, and it will continue to be called each time a row changes (via ListBox.rowChanged) and when the row before changes (either by ListBox.rowChanged on the previous row, or when the previous row becomes a different row). It is also called for all rows when ListBox.invalidateHeaders is called.