title: the event touchUpInside of a UIButton don't work
body: <p>there is only 1 cell in my UITableView, and I add a UIButton to the cell.
  set the action when touchUpInside event happens. But it doesn't work at all. Meanwhile, if 
  i set the trigger as touchDown event instead of touchUpInside, it will fire the action i set.</p>
  
  <p>I search the reason by google, someone says that the problem maybe caused by the superview's dimension. That is the size of the button is beyond its superview.
  so I add a UIView to contain the button, the code is as follow:</p>
  
  <pre><code>self.ageDisplay = [[UIButton buttonWithType:UIButtonTypeCustom] retain];
  UIImage *ageImage = [UIImage imageNamed:@"long_btn_click.png"];
  [self.ageDisplay setImage:ageImage forState:UIControlStateSelected];
  [self.ageDisplay setFrame:CGRectMake(10, 5, 145, 34)];//(10, 320, 145, 25)];
  [self.ageDisplay setTitle:@"请选择您的年龄" forState:UIControlStateNormal];
  [self.ageDisplay setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  [self.ageDisplay setTag:3];
  [self.ageDisplay addTarget:self action:@selector(showSelectionPage:) forControlEvents:UIControlEventTouchDown];
  
  self.buttonsSubView = [[UIView alloc] initWithFrame:CGRectMake(0, 310, 320, 106)];
  //self.buttonsSubView.backgroundColor = [UIColor blueColor];
  [self.buttonsSubView setUserInteractionEnabled:YES];
  [self.buttonsSubView addSubview:self.ageDisplay];
  </code></pre>
  
  <p>the above code is in ViewDidLoad function.</p>
  
  <pre><code>- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
  {
      NSString *sugPageCell = @"SuggestionPageCell";
      UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:sugPageCell];
      if (nil == cell)
      {
          cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:sugPageCell];
      }
  
      cell.selectionStyle = UITableViewCellSelectionStyleNone;
  
  
      [cell addSubview:self.sugTitle];
      [cell addSubview:self.sugSpecification];
      [cell addSubview:self.suggestion];
      self.buttonsSubView.userInteractionEnabled = YES;
      [cell addSubview:self.buttonsSubView];
  
      /*
      [cell addSubview:self.ageDisplay];
      [cell addSubview:self.genderDisplay];
      [cell addSubview:self.submit];
       */
  
      return cell;
  
  }
  </code></pre>
  
  <p>However, this doesn't help.
  The problem has confused me for 2 days.
  I will appreciate if anyone can provide some indication.
  Thank you. </p>