//=================================================

    //                 自定义SearchBar

    //=================================================

    // 1.创建一个UITextField作为背景

    UITextField *searchBar = [[UITextField alloc] init];

    searchBar.width = ;

    searchBar.height = ;

    searchBar.font = [UIFont systemFontOfSize:];

    searchBar.background = [UIImage imageNamed:@"searchbar_textfield_background"];

    // 2.添加左侧的小图标

//    UIImage *searchIcon = [UIImage imageNamed:@"searchbar_textfield_search_icon"];

//    UIImageView *searchIconView = [[UIImageView alloc] initWithImage:searchIcon]; // 使用此种形式创建出来的ImageView是有默认大小的。

    UIImageView *searchIconView = [[UIImageView alloc] init];

    searchIconView.image = [UIImage imageNamed:@"searchbar_textfield_search_icon"];

    searchIconView.width = ;

    searchIconView.height = ;

    searchIconView.contentMode = UIViewContentModeCenter;

    searchBar.leftView = searchIconView;

    searchBar.leftViewMode = UITextFieldViewModeAlways;

    self.navigationItem.titleView = searchBar;