Sets the selection function.
If set, this function is called before any node is selected or unselected, giving some control over which nodes are selected. The select function should return true if the state of the node may be toggled, and false if the state of the node should be left unchanged.
| this |
A `GtkTreeSelection`. |
| func |
The selection function. May be null |
| data |
The selection function’s data. May be null |
| destroy |
The destroy function for user data. May be null |