Saving State

You’ve build a marvellous app, configured your layout and the user arranged things just the way he likes. Great!

But the next time he opens the app he wants to find everything just the way he left it. Or (if you’re feeling fancy) choose from a number of saved layouts.

Strelit Layout offers a powerful persistence mechanism for that. Not only every aspect of the layout, also the state of the components within it can be converted into a serialisable object that can be saved to a database, to local storage or wherever else your heart desires.

Here’s how it works:

Creating the layout

For this tutorial we'll use the layout created in getting-started.

var config = {
    content: [{
        type: 'row',
        content:[{
            type: 'component',
            componentName: 'testComponent',
            componentState: { label: 'A' }
        },{
            type: 'column',
            content:[{
                type: 'component',
                componentName: 'testComponent',
                componentState: { label: 'B' }
            },{
                type: 'component',
                componentName: 'testComponent',
                componentState: { label: 'C' }
            }]
        }]
    }]
};

var myLayout = new StrelitLayout( config );

Listening for state changes

Your layout instance and all the items within it emit events. These bubble up, just like DOM events. The event we're interested in at the moment is called stateChanged. It is emitted whenever something happens that modifies the saveable layout state. Listening to it works like this:

myLayout.on( 'stateChanged', function(){
    //now save the state
});

The actual state object is created by calling myLayout.toConfig();. For our example we'll store it in the browser's localStorage.

myLayout.on( 'stateChanged', function(){
    var state = JSON.stringify( myLayout.toConfig() );
    localStorage.setItem( 'savedState', state );
});

Creating Layouts from saved states

So now the next time the user opens the app there's a choice. Either he has used it before and the app's state is stored in localStorage or he's using it for the first time and we provide a default config.

var myLayout,
    savedState = localStorage.getItem( 'savedState' );

if( savedState !== null ) {
    myLayout = new StrelitLayout( JSON.parse( savedState ) );
} else {
    myLayout = new StrelitLayout( config );
}

Saving Component States

So far we've only saved the layout's state, but what about the components within it, the ones you've build? Well, remember the componentState: { label: 'C' } entry that you've configured? This is just the initial state, the component itself can update it by calling container.extendState( state ); or container.setState( state );.

This stores it and emits a stateChanged event that bubbles up to the layout manager.

Let's update our testComponent to show a text input with a persistant value:

myLayout.registerComponent( 'testComponent', function( container, state ){

    // Create the input
    var input = $( '<input type="text" />' );

    // Set the initial / saved state
    if( state.label ) {
        input.val( state.label );
    }

    // Store state updates
    input.on( 'change', function(){
        container.extendState({
            label: input.val()
        });
    });

    // Append it to the DOM
    container.getElement().append( input );
});

And initialise the layout

myLayout.init();

The result

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