UITextField

    1.自定义搜索框
    UITextField *searchBar = [[UITextField alloc]init];
    searchBar.width = 300;
    searchBar.height = 30;
    //设置搜索框背景图片
    searchBar.background = [UIImage resizedImage:@"searchbar_textfield_background"];
    //设置内容居中：如果找到不到合适的属性，就去父类中找，contentVerticalAlignment就是父类中的属性
    searchBar.contentVerticalAlignment =  UIControlContentVerticalAlignmentCenter;
    //设置左边显示一个放大镜
    UIImageView *leftview = [[UIImageView alloc]init];
    leftview.image = [UIImage imageNamed:@"searchbar_textfield_search_icon"];
    leftview.width =30;
    leftview.height = searchBar.height;
    leftview.contentMode = UIViewContentModeCenter;  //leftView居中显示
    searchBar.leftViewMode = UITextFieldViewModeAlways;  //设置总是显示
    searchBar.leftView = leftview;
    //设置右边显示删除按钮
    searchBar.clearButtonMode = UITextFieldViewModeAlways;
    self.navigationItem.titleView = searchBar;