I am working on a visualforce page to overwrite the "new" button on a custom object. I have a parent object called Customer_Effort__c and a child object called Participant__c. This page is going to create a new Participant__c record. I need this page available for a list button on the related list for Participants on the Customer_Effort__c page layout.

I am new to visualforce and especially controller extensions, so I may have gotten myself turned around on this.

I am basically trying to create a new record based on a few user inputs and a specified parent record (customer_effort__c) from the record the button is clicked on.

Right now I am stuck with an error on the visualforce page of: Unknown constructor 'ParticipantControllerExtension.ParticipantControllerExtension(ApexPages.StandardSetController controller)'

Here is my Controller Extension:

public class ParticipantControllerExtension {

    private final Participant__c participant;
    String effort;
	
    public ParticipantControllerExtension(ApexPages.StandardController stdcontroller) {}
    
    public ParticipantControllerExtension() {
        effort = ApexPages.currentPage().getParameters().get('id');
    }
    public Participant__c getParticipant() {
        return participant;
    }
    public PageReference save() {
        participant.customer_effort__c = effort;
        update participant;

        return null;

    }
}

And here is my visualforce page:

<apex:page StandardController="Customer_Effort__c" recordSetVar="participants" extensions="ParticipantControllerExtension">
  <apex:form>
      <apex:pageBlock title="Add Participant">
          <br/><br/><apex:outputText value="Select a participant or a contact person. The account will added based on your input."/> <br/><br/><br/>
          <apex:pageBlockSection title="Participant Information">
              <apex:inputField value="{!participant.Participant__c}"/>
              <apex:inputField value="{!participant.Status__c}"/>
      	</apex:pageBlockSection>
          <apex:pageBlockSection title="Contact Person Information">
          <apex:inputField value="{!participant.Contact_Person__c}"/>
          </apex:pageBlockSection>
          	<apex:pageBlockButtons>
          		<apex:commandButton action="{!save}" value="Add to Event"/>
          	</apex:pageBlockButtons>
      </apex:pageBlock>
  </apex:form>
</apex:page>

Thank you so much for any help you can provide!