How do I show all the errors at once on a VF page?

Question

I am inserting some new records using the apex class. I wrote some error conditions; if the error condition matches it will return null and show the error message on the VF page for which the record failed.

But I want to show all errors at once instead of showing the only error where it stopped.

Is it possible?

Class:

List<StandardProduct__c> spList = new List<StandardProduct__c>();
for(Integer i=1;i<list.size();i++){
    val = list[i].split(',');
    StandardProduct__c sp = new StandardProduct__c();
    sp.xyProd_c = val[0];
    sp.xyqty_c = val[1];
    sp.xyPrice= val[2];
    if(sp.xyProd_c != 'Test'){ // If one record enters this condition it is stopping here and just showing only error for one record
        error.add('Invalid prod' + sp.xyProd_c);
        return null;
    }
    if(sp.xyqty_c != null && sp.xyPrice != null)
    {
        spList.add(sp);
    }
    else if(some condition){ // The same as the first condition, showing only one error which entered here
        error.add('Failed to upload' + sp.xyProd_c);
        return null;
    }
}

Answer 1

You must return outside your loop.

for (/*iteration*/)
{
    if (/*failure condition*/)
    {
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Fatal, 'message')));
    }
    // logic
    if (/*other failure condition*/)
    {
        ApexPages.addMessage(/*message construction*/);
    }
}
if (ApexPages.hasMessages(ApexPages.Severity.FATAL)) return null;

Answer 2

The problem is that you are returning from the function after you reach the first error. I can't see the whole picture from just what you've posted here, but part of the solution will be to remove the return null statements.