Treepanel in panel not showing the tree

[dragem]

does anyone know why this isn't working?

var mainPanel = Ext.create('Ext.panel.Panel', {        
        id: 'mainPanel',
        width: '100%',
        height: '100%',
        layout: 'border',
        collapsible: false,
        renderTo: Ext.getBody(),
        items: [
            {
                xtype: 'treepanel',
                id:'naviPanel',
                tbar: toolbar,
                width: 250,
                height: '100%',
                region: 'west',
                collapsible: false,
                useArrows: true,
                rootVisible: false,
                store: naviStore,
                multiSelect: true,
                singleExpand: true
            },{
                xtype: 'panel',
                id:'contentPanel',
                width: 500,
                height: '100%',
                region: 'center',
                collapsible: false
            }
        ]
    });

[scottmartin]

You are not specifying a height for your mainPanel. You are specify '100%' instead of height: 400
If you want a panel the size of your client window, use Viewport.

Viewport automatically renders to body, so there is no need to included that.

Scott.