Question

I wrote paging logic:

My requirement: total elements to display:100 per page,if i click next it should display next 100 records,if i click previous 100 records.

Initial varaible values:

• showFrom:1,
• showTo:100
• max elements:depends on size of data.
• pageSize:100.

Code:

if(paging.getAction().equalsIgnoreCase("Next")){
  paging.setTotalRec(availableList.size());
  showFrom = (showTo + 1);
  showTo = showFrom + 100- 1;
  if(showTo >= paging.getTotalRec())
    showTo = paging.getTotalRec();
  paging.setShowFrom(showFrom);
  paging.setShowTo(showTo);
}

else if(paging.getAction().equalsIgnoreCase("Previous")){
  showTo = showFrom - 1;
  showFrom = (showFrom - 100);
  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());
}

Here i can remove and add the elements to the existing data.above code works fine if i add and remove few elements.but if i remove or add 100 elements at a time counts are not displaying properly above code works fine if i add and remove few elements.

Answer 1

Some things to improve:

• replace “magic” value of 100 with final int PAGE_SIZE = 100;
• factor out redundant code.

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());

to outside of if/else to make your logic clearer

• Ensure that previous >= 0 and next <= number of records

Edit:

final int PAGE_SIZE = 100;
int numberOfPages = -1;
int currentPage = -1;

public void initializeVariables(){
  paging.setTotalRec(availableList.size());
  showFrom = 1; 
  showTo = PAGE_SIZE;
  //keep track of how many pages there should be
  numberOfPages = paging.getTotalRec()/PAGE_SIZE;
  currentPage = 1;
}

public void handlePagingAction(){
  if(paging.getAction().equalsIgnoreCase("Next")){
     if(currentPage < numberOfPages){
        ++currentPage;
     }
  }else if(paging.getAction().equalsIgnoreCase("Previous")){
     if(currentPage > 1){       
       --currentPage;
     }
  }      

  showFrom = (currentPage - 1) * PAGE_SIZE + 1;
  if(showFrom < 0){
    showFrom = 0
  }

  showTo = currentPage * PAGE_SIZE;
  if(showTo >= paging.getTotalRec()){
    showTo = paging.getTotalRec();
  }     

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
}