- UI界面的完美是一个好的产品的前提条件，最近开发在设置导航上左侧右侧的barbuttonItem 的时候由于设计想要距离左右有10的边距但是在更改customview的button的frame始终不起作用后来看下了关navigationItem的东西，从5.0以后系统多了两个属性，leftBarButtonItems和rightBarButtonItems两个数组类型的属性，也就是可以添加多个导航按钮，注意下api中提到的两点重要的：
- leftBarButtonItems are placed in the navigation bar<b> left to right </b>with the first
item in the list at the left outside edge and left aligned. - rightBarButtonItems are placed <b> right to left </b>with the first item in the list at
the right outside edge and right aligned.
- leftBarButtonItems are placed in the navigation bar<b> left to right </b>with the first
左侧的是从左到右边按照数组里的次序、右侧是从右向左 也就是说数组中的第一个放最右边，左侧的数组中的是第一个放最左边
UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
btn.frame= CGRectMake(0, 0, 40, 44);
[btn addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
UIBarButtonItem *btn_right = [[UIBarButtonItem alloc] initWithCustomView:btn];
UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
/**
width为负数时，相当于btn向右移动width数值个像素，由于按钮本身和 边界间距为5pix，所以width设为-5时，间距正好调整为0；width为正数 时，正好相反，相当于往左移动width数值个像素
*/
negativeSpacer.width = -5;
self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:negativeSpacer, btn_right, nil];
补充：导航控制器两侧的按钮颜色
self.navigationController.navigationBar.tintColor = [UIColorwhiteColor];**
