Passing parameters from referer/parent VF page to iframe/child VF page

referer.cls

public class Object_ext{

    public final Object__c ob;
    public String objId {get;set;}
    public String referer {get;set;}
    
    public Project_ext(ApexPages.StandardController stdController) {
        referer = ApexPages.currentPage().getHeaders().get('Referer');
            System.debug(referer); //Just to check!

        if(UserInfo.getUserType() != 'Standard'){ //If it's a community user,
            objId = getCommId(ApexPages.currentPage().getHeaders().get('Referer')); //then we pull the value from our parameter by examining the referer,
            ApexPages.currentPage().getParameters().put('id', objId); //and write that back to the page's ID parameter for the standard controller.
        }
        else {
            objId = ApexPages.currentPage().getParameters().get('Id'); //Otherwise, for internal users, just pull down the parameter.
        }

        this.ob= (Object__c)stdController.getRecord();
    }
    
    public String getCommId(String referer){
        String comStr = 'id=';
        return referer.substring(referer.indexOf(comStr)+3, referer.indexOf(comStr)+21);  //This will always be looking for an 18-digit char ID.
    }

}