Your First Component

This page is intended for developers of Crystal Toolkit who want to add a new MPComponent to support interactive viewing of an MSONable object, such as crystal structures, phase diagrams, etc.


Crystal Toolkit is built on top of Dash by Plotly. Dash is a framework to build rich, interactive web apps purely from Python with no JavaScript knowledge required. If you’re not familiar with the Dash framework, please read their documentation and try their example app first.

The basic steps are to:

  1. Sub-class MPComponent. Recognize that the component comes with a dcc.Store which contains the MSON representation of whatever the component is intended to render.

  2. Implement its master layout() method to return the “default” layout for your component. You may also add additional ..._layout() methods for optional layouts; for example, the StructureMoleculeComponent has legend_layout() to return the legend for the structure or molecule being displayed.

    The _sub_layouts method, which returns a dictionary with values corresponding to different parts of your component, is available for book-keeping if your component is complex.

  1. For interactivity, implement the generate_callbacks(app, cache) method. Inside this method you can define callbacks to be associated with the component. At minimum, make sure that if the component’s main dcc.Store is updated with a new object (for example, a new crystal structure is set for StructureMoleculeComponent) that the state of the component is also updated appropriately.

    Try to keep the total number of callbacks to a minimum, and the size of the data stores small wherever possible, to improve performance of your component. Using multiple-output callbacks, and judicious use of raise PreventUpdate and return no_update can help with this, especially if checking for the initial callback firing on page load.

    If you have a long-running callback, or one that may be long-running, make sure to wrap it in a dcc.Loading component to improve the user experience.

At this point, the component should be working. It needs a simple example app to be added to crystal_toolkit.apps.examples and a corresponding test that the example app runs, and finally a short documentation page in docs_rst. Please copy from the existing examples as necessary.