Trait DataGenerator 

pub trait DataGenerator<Index> {
    type Data;
    type Key: DataKey;
    type Item: Clone + Default + PartialEq;

    // Required methods
    fn update(&mut self, data: &Self::Data) -> GeneratorChanges<Index>;
    fn len(&self, data: &Self::Data, lbound: Index) -> DataLen<Index>;
    fn key(&self, data: &Self::Data, index: Index) -> Option<Self::Key>;
    fn generate(&self, data: &Self::Data, key: &Self::Key) -> Self::Item;
}

A generator for use with GeneratorClerk

This provides a substantially simpler interface than DataClerk.

Required Associated Types

type Data

Input data type (of parent widget)

Data of this type is passed through the parent widget; see Widget::Data and the Events trait. This input data might be used to access a data set stored in another widget or to pass a query or filter into the DataClerk.

Note that it is not currently possible to pass in references to multiple data items (such as an external data set and a filter) via Data. This would require use of Generic Associated Types (GATs), not only here but also in the Widget trait; alas, GATs are not (yet) compatible with dyn traits and Kas requires use of dyn Widget. Instead one can share the data set (e.g. Rc<RefCell<DataSet>>) or store within the DataClerk using the clerk / clerk_mut methods to access; in both cases it may be necessary to update the view controller explicitly (e.g. cx.update(list.as_node(&input))) after the data set changes.

type Key: DataKey

Key type

All data items should have a stable key so that data items may be tracked through changing queries. This allows focus and selection to correctly track items when the data query or filter changes.

Where the query is fixed, this can just be the Index type.

type Item: Clone + Default + PartialEq

Item type

This is the generated type.

Required Methods

fn update(&mut self, data: &Self::Data) -> GeneratorChanges<Index>

Update the generator

This is called by kas::Events::update. It should update self as required reflecting possible data-changes and indicate through the returned GeneratorChanges value the updates required to tokens and views.

Note: this method is called automatically when input data changes. When data owned or referenced by the DataClerk implementation is changed it may be necessary to explicitly update the view controller, e.g. using ConfigCx::update or Action::UPDATE.

This method may be called frequently and without changes to data.

fn len(&self, data: &Self::Data, lbound: Index) -> DataLen<Index>

Get the number of indexable items

Scroll bars and the index values passed to Self::generate are limited by the result of this method.

Where the data set size is a known fixed len (or unfixed but with maximum len <= lbound), this method should return DataLen::Known(len).

Where the data set size is unknown (or unfixed and greater than lbound), this method should return DataLen::LBound(lbound).

lbound is set to allow scrolling a little beyond the current view position (i.e. a little larger than the last prepared range.end).

fn key(&self, data: &Self::Data, index: Index) -> Option<Self::Key>

Get a key for a given index, if available

This method should be fast since it may be called repeatedly. This method is only called for index less than the result of Self::len.

This may return None even when index is within the query’s range since data may be sparse; in this case the view widget at this index is hidden.

fn generate(&self, data: &Self::Data, key: &Self::Key) -> Self::Item

Generate an item

The key will be the result of Self::key for an index less than Self::len.

Implementors