How to write code to display all user-friendly error messages on the UI for Apex / Visualforce?

Question

Visualforce page is displaying one error message at a time not all error messages if validation is failed for all fields.Below is my code in the controller.I have apex:pagemessages in visualforce page is display error messages

if((newFR.Fleet_Vehicle_Maintained__c == 'No')&& (newFR.Fleet_Explanation__c == NULL )) {
          newFR.Fleet_Explanation__c.addError('If the fleet vehicle is not being maintained by the rep, an explanation is required.');
                        return null;
          }
         if((newFR.Rep_Policy__c == 'No')&& (newFR.Not_Policy_Explanation__c == NULL )) {
           newFR.Not_Policy_Explanation__c.addError('Not_Following_Policy_Explanation__c');

          return null;
          } 
          if((newFR.FR_Status__c == 'Send for Representative')&& (newFR.Review_Date__c > system.today() )) {
           newFR.Review_Date__c.addError('Review Date cannot be a future date when sending  for acknowledgement.');

          return null;
          } 

Answer 1

The code you've produced is quitting after the first error (return null). A more usual scenario is to set a flag when validation fails, then check for the flag at the end of the validation to abort processing.

Here's a common example:

public PageReference doSomething() {
    Boolean okayToSave = true;
    if( condition1 ) {
        record.field1__c.addError(...);
        okayToSave = false;
    }
    if( condition2 ) {
        record.field2__c.addError(...);
        okayToSave = false;
    }
    if( conditionN ) {
        record.fieldN__c.addError(...);
        okayToSave = false;
    }
    if( !okayToSave ) {
        return null;
    }
    // Now save the data
    insert record;
    return Page.SuccessfulSave;
}

Of course, I left out the part where you use a try-catch block or other error handling for the actual save, because it's not relevant to what I'm trying to explain.

Answer 2

You are using the addError field which relates to the <apex:message> and <apex:messages> tags. If you want use your existing code then you would need to use somethign like this

ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'This is apex:pageMessages'));

or you could change your vf tag to <apex:messages> and it should work with your apex code.

Jesse Altman has an excellent answer on here for this very subject. I would take a look at it. It really helped me to understand the difference. This explanation is the only place I have seen them all compared in one place and is an excellent resource.

Difference between the multiple messaging options in Visualforce?