获取UISearchBar上的UITextField

获取UISearchBar上的UITextField并对其操作：

    UITextField *searchField = [_searchBar valueForKey:@"_searchField"];
//获取只需要上面一句话
    searchField.tag = 100;
    searchField.textColor = fontBlackColor;
    searchField.backgroundColor = Bg_Grey;
    [searchField setLeftViewMode:UITextFieldViewModeNever];
    [searchField setRightViewMode:UITextFieldViewModeNever];
    [searchField setValue:fontGreyColor forKeyPath:@"_placeholderLabel.textColor"];
    [searchField becomeFirstResponder];

        [searchField setValue:[UIFont systemFontOfSize:12]forKeyPath:@"_placeholderLabel.font"];

        [searchField setBorderStyle:UITextBorderStyleNone];

        searchField.layer.borderWidth = 3.0f;

        searchField.layer.cornerRadius = 10.0f;

        searchField.layer.borderColor = [UIColor clearColor].CGColor;

        searchField.clearButtonMode=UITextFieldViewModeNever;