<apex:page standardController="Training__c" extensions="Trainingsurveylistbutton" action="{!surveylist}"  recordSetVar="list button"> 
<apex:messages style="text-align:center;color:red;"/>
</apex:page>
                                        

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corresponding apex class:

 public with sharing class Trainingsurveylistbutton {
public List<training__c> t2;
public set<string> Set1;
public boolean pageblockCheck{set;get;}
//public List<training__c> l1 = New List<training__c>();
    public Trainingsurveylistbutton(ApexPages.StandardSetController controller) {
   
    t2 = new list <training__c>();
    t2=Controller.getSelected();
    system.debug('++++++++++T2::::'+t2);
    if(t2.size()<=0)
        {
       //for(training__c s1 : t2){
       //s1.addError('Please select atleast one record from list view you wish to update');
       // }
       ApexPages.Message errMsg = new ApexPages.Message(ApexPages.Severity.WARNING, 'Please select atleast one record from list view you wish to update');  
            ApexPages.addMessage(errMsg);

        }
        else{
  
      Here i am used set- to get all selected record id  . but i want to get all selected record field .. how to get selected record  under all field .Please give ur idea.i want to use those selected record field -below surveylist() method.i have marked red
            set1 = New set<string>();
           for(training__c ss : t2){
               system.debug('::::ss.Id::::'+ss);
               // Set1.add(ss.ID);
               system.debug('++++++++++set1'+set1);
            }

 
}
    }
    public void surveylist()
    {
    // Sweep training object for day 2 , 3 & 5th day survey
       //List <training__c> t1 = new list <training__c>();
       list <training_survey__c> ts2 = new list<training_survey__c>();
       t2 = [ select id,day1surveyflag__c,T__c, day3surveyflag__c, day5surveyflag__c from training__c];// where day1surveyflag__c = true or day3surveyflag__c = true or day5surveyflag__c = true or T__c='Day 1' ];
      for(string lx : set1)
      {  
        system.debug('*********lx'+lx);
        
        training_survey__c ts = new training_survey__c();
        training__c tr = new training__c();
     

 here i want to add logic here:please give ur idea:

1.If a Survey record has already been created for the specific Day, we just need to resend the 
existing survey record link..(purpose:survey was not filled by person within the 
timeframes specified)

        integer ts1=[select count() from training_survey__c where Training__c =: lx];
        system.debug('**count'+ts1);
        if(ts1==1)
        {
        
          ts=[select id,Training__c,survey_type__c from training_survey__c where Training__c =: lx];
          
          system.debug('*************ts'+ts.survey_type__c);
               
              if(ts.Survey_Type__c == 'Day1') 
              {
                ts.sample__c = 'one day';
              }
          //   ts2.add(ts);
          }
          update ts;
           system.debug('*************ts'+ts.survey_type__c);

     //   if(ts2 != null )
     //              {
      //                  update ts2;  
      //             } 
        
        if (ts1==0)
                {    
                   ts.training__C = lx;
                   ts.Survey_Type__c = 'Day1';
                // }
                   ts2.add(ts); 
                   
               if(ts2 != null )
                  {
                        insert ts2;  
                   } 
                 }
            }
       }

-----------------------------------------------------

Training survey process:

I have two object.Training and training survey...training record lookup relationship with training
survey.training object have training start date custom field...training survey have traning__c
lookup field.Traing survey have survey type custom field.
Process: if training start date --today+1,today+2,today+3--will send trainingsurvey email (day 1
or day 2 or day3 )to corresponding taining object record.else will send drop training survey.i
have set formula field check box..day 1 flag,day3,day5--whenever flag true -i have created
schedule process...apex class will insert survey type under traning survey object .i have created
workflow email alert -when will u insert survey type will send corresponding survey to corresponding records.

Please give ur idea for that process or  i am used set above classes -(above  i am mentioned in red line)- to get all selected record id  . but i want to get all selected record field .. how to get selected record  under all field .Please give ur idea.i want to use those selected record field -below surveylist() method.i have marked red