Visualforce Error: Return type of an Apex action method must be a PageReference. Found: core.apexpages.el.adapters.ApexListELAdapter

Question

I deleted the previous code that I had on this post.

I modified my code again:

Now I am getting this error If I press the Search Button from VF page:

Return type of an Apex action method must be a PageReference. Found: core.apexpages.el.adapters.ApexListELAdapter

public class WrapperDemoController2{

public String sfprn { get; set; }
public String searchPatients { get; set; }
public String mrn {get;set;}

public class TableRow2{
    public String sfprn {get;set;}
    public String mrn {get;set;}
    public Decimal SurveySelection {get;set;}
}

public List<TableRow2> RowList {get; set;}

public List<TableRow2> searchPatients(){

    RowList = new List<TableRow2>();
    TableRow2 tr;

    for(Patient__c con : [SELECT sfprn__c, 
                                mrn__c, 
                                (select SurveySelection__c.SurveySelection__c from SurveySelections__r) 
                                FROM Patient__c
                                where mrn__c =:mrn                                    
                                ]){

        tr = new TableRow2();
        tr.sfprn = con.sfprn__c;
        tr.mrn = con.mrn__c;
        tr.SurveySelection = con.SurveySelections__r.isEmpty() ? null : con.SurveySelections__r[0].SurveySelection__c;

        RowList.add(tr);
        }
     return RowList;   
}    

}

---

<apex:page Controller="WrapperDemoController2">
<apex:form >
<apex:pageBlock >
    <!-- Serarch button-->
    <apex:pageBlockButtons location="top">
        <apex:commandButton value="Search" action="{!searchPatients}" reRender="contact-table"/>
    </apex:pageBlockButtons>

    <apex:pageBlockSection id="contact-table" columns="1">
        <!-- Input -->
        <apex:pageBlockSectionItem >
            <apex:outputLabel value="MRN" />
            <apex:inputText value="{!mrn}"/>

        </apex:pageBlockSectionItem>
        </apex:pageBlockSection>

        <!-- Output --->
        <apex:pageBlockTable value="{!RowList}" var="c">
            <apex:column value="{!c.mrn}"/>
            <apex:column value="{!c.sfprn}"/>
            <apex:column value="{!c.SurveySelection}"/>
        </apex:pageBlockTable>   
</apex:pageBlock>

Answer 1

Currently you have search logic in constructor "WrapperDemoController2". It loads everytime the page loads. You dont need to specify action.

But if you want this logic to run everytime when button is clicked, move that logic to a new method like follows,

public List<TableRow2> searchResults(){

    RowList = new List<TableRow2>();
    TableRow2 tr;

    for(Patient__c con : [SELECT sfprn__c, 
                                mrn__c, 
                                (select SurveySelection__c.SurveySelection__c from SurveySelections__r) 
                                FROM Patient__c
                                where mrn__c =:mrn                                    
                                ]){

        tr = new TableRow2();
        tr.sfprn = con.sfprn__c;
        tr.mrn = con.mrn__c;
        tr.SurveySelection = con.SurveySelections__r.isEmpty() ? null : con.SurveySelections__r[0].SurveySelection__c;

        RowList.add(tr);

    }
    return RowList;
}

VF Page:

<apex:commandButton value="Search" action="{!searchResults}" reRender="contact-table"/>

Answer 2

I got the solutions (two changes) : I needed to change from: public List searchPatients() to: public PageReference searchPatients()

And return statment must be set to null Changed from: return RowList; to: return null;