title: How to use pushViewController and popViewController
body: <p>I want to A viewcontroller switch another B viewcontroller,First time,I push(press GuestBook Button)and TableView get information ok,and press back Button ok, push(press GuestBook Button) again,JSON data <code>NSLog</code> have message,but tableview data not appear!
  what's happen?</p>
  
  <p>PS:i use storyboard!Have a custom cell xib!</p>
  
  <p>A.m</p>
  
  <pre><code>- (IBAction)toHostGuestBook:(id)sender {
      hgbvc = [self.storyboard instantiateViewControllerWithIdentifier:@"ToHostGuestBookSegue"];
      hgbvc.eventidStr = eventidStr;
      NSLog(@"hgbvc.eventidStr:%@",hgbvc.eventidStr);
      [self.navigationController pushViewController:hgbvc animated:YES];
  
  }
  </code></pre>
  
  <p>B.m</p>
  
  <pre><code>- (IBAction)backToHostMainEventDetail:(id)sender {
      [self.navigationController popViewControllerAnimated:YES]; 
  }
  </code></pre>
  
  <p>B.m</p>
  
  <pre><code>// Customize the appearance of table view cells.
  - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
  
      static NSString *GuestBookCellIdentifier = @"GuestBookCellIdentifier";
  
      static BOOL nibsRegistered = NO;
      if (!nibsRegistered) {
          UINib *nib = [UINib nibWithNibName:@"GuestBookCell" bundle:nil];
          [tableView registerNib:nib forCellReuseIdentifier:GuestBookCellIdentifier];
          nibsRegistered = YES;
      }
  
      gbcell = [tableView dequeueReusableCellWithIdentifier:GuestBookCellIdentifier];
      if (gbcell == nil) {
          gbcell = [[GuestBookCell alloc]
                     initWithStyle:UITableViewCellStyleDefault
                     reuseIdentifier:GuestBookCellIdentifier];
      }
  
      NSDictionary *dict = [messageRows objectAtIndex: indexPath.row];
  
      gbcell.nicknameStr = [dict objectForKey:@"vusr"];
      gbcell.dateStr = [dict objectForKey:@"date"];
      gbcell.messageStr = [dict objectForKey:@"message"];
  
  
      return gbcell;
  
  }
  </code></pre>