请问下我的这个下拉菜单，一拉出来就被别的覆盖掉了，怎么办？

我想让他点出来的时候在最上面

下面的是我的代码
//设置商品分类的子分类
_comboBoxClass = [[ComboBoxView alloc] initWithFrame:CGRectMake(180, 120, 100 , 130)];
_comboBoxClass.comboBoxDatasource = comboBoxDatasource;
_comboBoxClass.backgroundColor = [UIColor clearColor];
[ _comboBoxClass setContent:[comboBoxDatasource objectAtIndex:0]];
[self.view addSubview: _comboBoxClass];

• (id)initWithFrame:(CGRect)frame { if ((self = [super initWithFrame:frame])) { [self initVariables]; [self initCompentWithFrame:frame]; } return self; }

#pragma mark -
#pragma mark custom methods

• (void)initVariables {
  _showComboBox = NO;
  }

• (void)initCompentWithFrame:(CGRect)frame {
  _selectContentLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 0, 60, 25)];
  _selectContentLabel.font = [UIFont systemFontOfSize:14.0f];
  _selectContentLabel.backgroundColor = [UIColor clearColor];
  [self addSubview:_selectContentLabel];

  _pulldownButton = [UIButton buttonWithType:UIButtonTypeCustom];
  [_pulldownButton setFrame:CGRectMake(frame.size.width - 25, 0, 25, 25)];
  [_pulldownButton setBackgroundImage:[UIImage imageNamed:@"list_ico_d"] forState:UIControlStateNormal];
  [_pulldownButton addTarget:self action:@selector(pulldownButtonWasClicked:) forControlEvents:UIControlEventTouchUpInside];
  [self addSubview:_pulldownButton];

  _hiddenButton = [UIButton buttonWithType:UIButtonTypeCustom];
  [_hiddenButton setFrame:CGRectMake(0, 0, frame.size.width - 25, 25)];
  _hiddenButton.backgroundColor = [UIColor clearColor];
  [_hiddenButton addTarget:self action:@selector(pulldownButtonWasClicked:) forControlEvents:UIControlEventTouchUpInside];
  [self addSubview:_hiddenButton];

  _comboBoxTableView = [[UITableView alloc] initWithFrame:CGRectMake(1, 26, frame.size.width -2, frame.size.height - 27)];
  _comboBoxTableView.dataSource = self;
  _comboBoxTableView.delegate = self;
  _comboBoxTableView.backgroundColor = [UIColor clearColor];
  _comboBoxTableView.separatorColor = [UIColor blackColor];
  _comboBoxTableView.hidden = YES;
  [self addSubview:_comboBoxTableView];

}

• (void)setContent:(NSString *)content {
  _selectContentLabel.text = content;
  }

• (void)show {
  _comboBoxTableView.hidden = NO;
  _showComboBox = YES;
  [self setNeedsDisplay];
  }

• (void)hidden {
  _comboBoxTableView.hidden = YES;
  _showComboBox = NO;
  [self setNeedsDisplay];
  }

#pragma mark -
#pragma mark custom event methods

• (void)pulldownButtonWasClicked:(id)sender { if (_showComboBox == YES) { [self hidden]; }else { [self show]; } }

#pragma mark -
#pragma mark UITableViewDelegate and UITableViewDatasource methods

• (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
  return [_comboBoxDatasource count];
  }

• (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
  static NSString *CellIdentifier = @"ListCellIdentifier";
  UITableViewCell *cell = [_comboBoxTableView dequeueReusableCellWithIdentifier:CellIdentifier];
  if (cell == nil) {
  cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] ; }
  cell.textLabel.text = (NSString *)[_comboBoxDatasource objectAtIndex:indexPath.row];
  cell.textLabel.font = [UIFont systemFontOfSize:13.0f];
  cell.accessoryType = UITableViewCellAccessoryNone;
  cell.selectionStyle = UITableViewCellSelectionStyleNone;

  return cell;
  }
  //设置tableview的数据靠左
  -(void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
  {
  if ([cell respondsToSelector:@selector(setSeparatorInset:)])
  { [cell setSeparatorInset:UIEdgeInsetsZero]; }
  if ([cell respondsToSelector:@selector(setPreservesSuperviewLayoutMargins:)])
  { [cell setPreservesSuperviewLayoutMargins:NO]; }
  if ([cell respondsToSelector:@selector(setLayoutMargins:)])
  { [cell setLayoutMargins:UIEdgeInsetsZero]; }}

• (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
  return 25.0f;
  }

• (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
  [self hidden];
  _selectContentLabel.text = (NSString *)[_comboBoxDatasource objectAtIndex:indexPath.row];
  }

• (void)drawListFrameWithFrame:(CGRect)frame withContext:(CGContextRef)context {
  CGContextSetLineWidth(context, 1.0f);
  CGContextSetRGBStrokeColor(context, 0.0f, 0.0f, 0.0f, 1.0f);
  if (_showComboBox == YES) {
  CGContextAddRect(context, CGRectMake(0.0f, 0.0f, frame.size.width, frame.size.height));

  }else {
  CGContextAddRect(context, CGRectMake(0.0f, 0.0f, frame.size.width, 25.0f));
  }
  CGContextDrawPath(context, kCGPathStroke);
  CGContextMoveToPoint(context, 0.0f, 25.0f);
  CGContextAddLineToPoint(context, frame.size.width, 25.0f);
  CGContextMoveToPoint(context, frame.size.width - 25, 0);
  CGContextAddLineToPoint(context, frame.size.width - 25, 25.0f);

  CGContextStrokePath(context);
  }

#pragma mark -
#pragma mark drawRect methods

• (void)drawRect:(CGRect)rect { [self drawListFrameWithFrame:self.frame withContext:UIGraphicsGetCurrentContext()]; }

#pragma mark -
#pragma mark dealloc memery methods

@end

这是先添加下拉，再加3，下拉就在3下面了，试试点击后添加到view，选择后隐藏