tornadofx-guide

Advanced Data Controls
Assign If Null
If you have a reason for wanting to recreate the graphic property for a list cell, you can use
the assignIfNull helper, which will assign a value to any given property if the property
doesn't already contain a value. This will make sure that you avoid creating new nodes if
updateItem is called on a cell that already has a graphic property assigned.
cellFormat {
graphicProperty().assignIfNull {
label("Hello")
}
}
ListCellFragment
The ListCellFragment is a special fragment which can help you manage ListView cells. It
extends Fragment , and includes some extra ListView specific fields and helpers. You
never instantiate these fragments manually, instead you instruct the ListView to create
them as needed. There is a one-to-one correlation between ListCell and
ListCellFragment instances. Only one ListCellFragment instance will over its lifecycle be
used to represent different items.
To understand how this works, let's consider a manually implemented ListCell , essentially
the way you would do in vanilla JavaFX. The updateItem function will be called when the
ListCell should represent a new item, no item, or just an update to the same item. When
you use a ListCellFragment , you do not need to implement something akin to updateItem ,
but the itemProperty inside it will update to represent the new item automatically. You can
listen to changes to the itemProperty , or better yet, bind it directly to a ViewModel . That
way your UI can bind directly to the ViewModel and no longer need to care about changes to
the underlying item.
Let's recreate the form from the cellFormat example using a ListCellFragment . We need a
ViewModel which we will call PersonModel (Please see the Editing Models and Validation
chapter for a full explanation of the ViewModel ) For now, just imagine that the ViewModel
acts as a proxy for an underlying Person , and that the Person can be changed while the
observable values in the ViewModel remain the same. When we have created our
PersonCellFragment , we need to configure the ListView to use it:
listview(personlist) {
}
cellFragment(PersonCellFragment::class)
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