我UIActionSheet的显示时是透明的。我该如何改变?这是问题的截图:

编码:
   - (IBAction)btnTakePicture_Clicked:(id)sender
{
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:@"Select Image from..." delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles:@"Camera", @"Image Gallary", nil];
    actionSheet.actionSheetStyle = UIActionSheetStyleBlackTranslucent;
    actionSheet.alpha=0.90;
    actionSheet.tag = 1;
    [actionSheet showInView:self.view];
    UIButton *btn = (UIButton *)sender;
    intButton = btn.tag;
}