/*This trigger should update a custom object in Saleforce after a User is being updated or inserted
Instead it throws the following exception. 
MIXED_DML_OPERATION, DML operation on non-setup object is not supported after you have updated a setup object: SF_User__c: [Id]: 
Trigger.UsersTableChangedUpdateSFUserC: line 33, column 20 
Who can help me out with this one... Thx in advance.
*/ 
trigger UsersTableChangedUpdateSFUserC on User (after insert, after update) {
    if (Trigger.isInsert) {
        for (User u : Trigger.new) {
            SF_User__c newUser = new SF_User__c(
                Username__c = u.Username,
                Name__c = u.Name,
                UserId__c = u.Id);

            insert newUser;
        }
    }
    else
    {
       for (Integer i = 0; i < System.Trigger.new.size(); i++) {
           //get all updates
           String userID = System.Trigger.new[i].Id;
                 
           Integer count = [select count() from SF_User__c where UserId__c = :userID];
           if (count >0) {
               //update
               //SF_User__c updateUser = [select Id,  UserId__c, Naam__c, Gebruikersnaam__c from SF_User__c where UserId__c = :userID];                         
            
               //update updateUser ;
           }
           else{
             //insert
               
               for (User u : Trigger.new) {
                   SF_User__c newUser = new SF_User__c(
                   Username__c = u.Username,
                   Name__c = u.Name,
                   UserId__c = u.Id);

                   insert newUser;
               }                     
           }
      
        }    
    }
}