Understanding Tapestry Principle 1. "Static Structure, Dynamic Behaviour"

I'm learning tapestry 5 web framework but I don't understand the principle 1 about it: "Static Structure, Dynamic Behaviour", what does means it ?

If I don't add components to the components, how can I create a dynamic page?

anyone can help me? Thanks in advance

Solution

It means that you can't choose or replace components at runtime effectively.

If, say, you'd want to build a portal solution where users could arrange components on a screen any way they wanted, Tapestry would not offer an effective way to do that, because components have static structure, i.e. you must define what goes into them at compile-time in their template file.

Or you might have a specialized menu for administrators, so you might want to just replace the Menu component with a derived component, AdminMenu - but you can't, you have to use if statements in the template or use a block to inject different menus into your layout component.

There's an anti-pattern related to this limitation: The God or über-component tries to solve this problem by effectively having a giant template file with all the available components, like this:

<t:if t:test="displayComponentA">
     <span t:type="ComponentA" ... />
</t:if>
<t:if t:test="displayComponentB">
     <span t:type="ComponentB" ... />
</t:if>
...

This, however, is horribly ineffective, as Tapestry assembles the entire component tree, including components that are not displayed, to do the rendering of the page.