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# Virtual List

The virtual List is a widget based on the framework's virtual infrastructure.

## Preview Image

## Description

The `qx.ui.list.List` is based on the virtual infrastructure and supports filtering, sorting, grouping, single selection, multi selection, data binding and custom rendering.

Using the virtual infrastructure has considerable advantages when there is a huge amount of model items to render: Widgets are created only for visible items and reused. This saves both creation time and memory.

With the qx.ui.list.core.IListDelegate interface, it is possible to configure the list's behavior (item and group renderer configuration, filtering, sorting, grouping, etc.).

Note

At the moment we only support widget based rendering for list and group items, but we are planning to also support HTML based rendering in a future release.

## Code Example

Here's an example. We create a simple list example with 2500 items, sort the items (ascending), select the 20th item and log each selection change.

    //create the model data
    var rawData = [];
    for (var i = 0; i < 2500; i++) {
      rawData[i] = "Item No " + i;
    }
    var model = qx.data.marshal.Json.createModel(rawData);

    //create the list
    var list = new qx.ui.list.List(model);

    //configure the lists's behavior
    var delegate = {
      sorter : function(a, b) {
        return a > b ? 1 : a < b ? -1 : 0;
      }
    };
    list.setDelegate(delegate);

    //Pre-Select "Item No 20"
    list.getSelection().push(model.getItem(20));

    //log selection changes
    list.getSelection().addListener("change", function(e) {
      this.debug("Selection: " + list.getSelection().getItem(0));
    }, this);

## Demos

Here are some links that demonstrate the usage of the widget:

- Example for the virtual List widget
- Example showing the filtering feature
- Example showing the custom rendering
- Example showing the grouping feature

## API

Here is a link to the API of the widget:
qx.ui.list.List