Render section or display error message

Question

I have a requirement where I want a section to render depending on a value of a controller variable. If the section is not rendered I want an error message to be displayed. I have the following piece of code

<apex:pageblock rendered="{!AModel.enableSection}">

I want something like this

if enablesection is true render page block else display String message 'Section cannot be rendered'

Answer 1

<apex:pageblock rendered="{!AModel.enableSection}">

<apex:pageMessages rendered="{!NOT(AModel.enableSection)}"/>

Use apexPageMessage with Rendered

And in controller use

ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Error,'Section cannot be rendered'));