ios5及其以后提供了一个比较强大的工具uiappearance，我们通过uiappearance设置一些ui的全局效果，这样就可以很方便的实现ui的自定义效果又能最简单的实现统一界面风格，它提供如下两个方法。
+ (id)appearance
这个方法是统一全部改，比如你设置uinavbar的tintcolor，你可以这样写：[[uinavigationbar appearance] settintcolor:mycolor];
+ (id)appearancewhencontainedin:(class <>)containerclass,...
这个方法可设置某个类的改变：例如：设置uibarbuttonitem 在uinavigationbar、uipopovercontroller、uitabbar中的效果。就可以这样写
[[uibarbuttonitem appearancewhencontainedin:[uinavigationbar class], [uipopovercontroller class],[uitabbar class] nil] settintcolor:mypopovernavbarcolor];
请注意＊使用appearance设置ui效果最好采用全局的设置，在所有界面初始化前开始设置，否则可能失效。
支持uiappearance协议的类可以访问appearance selector ,它为receiver返回appearance proxy，我么可以给proxy发一些消息，诸如settintcolor:等
但是它并不是支持所有的ui类。下面列出它支持的类
1.uiactivitiindicatorview
2.uibarbuttonitem
3.uibaritem
4.uinavgationbar
5.uipopovercontroll
6.uiprogressview
7.uisearchbar
8.uisegmentcontroll
9.uislider
10.uiswitch
11.uitabbar
12.uitabbaritem
13.uitoolbar
14.uiview
15.uiviewcontroller
具体ui外观修改如下：
1.修改导航栏背景
代码如下:
uinavigationbar * appearance = [uinavigationbar appearance];
uiimage *navbackgroundimg =[uiimage imagenamed:@navbg.png”];
[appearance setbackgroundimage:navbackgroundimgforbarmetrics:uibarmetricsdefault];
2.标签栏（uitabbar）
代码如下:
uitabbar *appearance = [uitabbar appearance];
//设置背景图片
[appearance setbackgroundimage:[uiimage imagenamed:@tabbar_bg.png]];
//门置选择item的背景图片
uiimage * selectionindicatorimage =[[uiimageimagenamed:@tabbar_slider]resizableimagewithcapinsets:uiedgeinsetsmake(4, 0, 0,0)] ;
[appearance setselectionindicatorimage:selectionindicatorimage];
3.分段控件（uisegmentcontrol）
代码如下:
uisegmentedcontrol *appearance = [uisegmentedcontrol appearance];
//segmenteg正常背景
[appearance setbackgroundimage:[uiimage imagenamed:@segmente.png]
forstate:uicontrolstatenormal
barmetrics:uibarmetricsdefault];
//segmente选中背景
[appearance setbackgroundimage:[uiimage imagenamed:@segmente_a.png]
forstate:uicontrolstateselected
barmetrics:uibarmetricsdefault];
//segmente左右都未选中时的分割线
//barmetrics表示navigation bar的状态，uibarmetricsdefault 表示portrait状态（44pixel height），uibarmetricslandscapephone 表示landscape状态（32pixel height）
[appearance setdividerimage:[uiimage imagenamed:@segmente_line.png]
forleftsegmentstate:uicontrolstatenormal
rightsegmentstate:uicontrolstatenormal
barmetrics:uibarmetricsdefault];
[appearance setdividerimage:[uiimage imagenamed:@segmente_line.png]
forleftsegmentstate:uicontrolstateselected
rightsegmentstate:uicontrolstatenormal
barmetrics:uibarmetricsdefault];
[appearance setdividerimage:[uiimage imagenamed:@segmente_line.png]
forleftsegmentstate:uicontrolstatenormal
rightsegmentstate:uicontrolstateselected
barmetrics:uibarmetricsdefault];
//字体
nsdictionary *textattributes1 = @{uitextattributefont: [uifont systemfontofsize:18],
uitextattributetextcolor: [uicolor bluecolor],
uitextattributetextshadowcolor: [uicolor whitecolor],
uitextattributetextshadowoffset: [nsvaluevaluewithcgsize:cgsizemake(1, 1)]};
[appearance settitletextattributes:textattributes1 forstate:1];
nsdictionary *textattributes2 = @{uitextattributefont: [uifont systemfontofsize:18],
uitextattributetextcolor: [uicolor whitecolor],
uitextattributetextshadowcolor: [uicolor blackcolor],
uitextattributetextshadowoffset: [nsvaluevaluewithcgsize:cgsizemake(1, 1)]};
[appearance settitletextattributes:textattributes2 forstate:0];
4.uibarbutton
注意：uibarbutton有leftbarbutton，rightbarbutton和backbarbutton，其中backbarbutton由于带有箭头，需要单独设置。
barbutton背景设置是ios6.0及以后的，而backbutton是ios5.0及以后的，这里要注意！
代码如下:
//修改导航条上的uibarbuttonitem
uibarbuttonitem *appearance = [uibarbuttonitem appearancewhencontainedin:[uinavigationbar class], nil];
//设置导航栏的字体包括backbarbutton和leftbarbutton，rightbarbutton的字体
nsdictionary *textattributes = @{uitextattributefont: [uifontsystemfontofsize:18],
uitextattributetextcolor: [uicolorbluecolor],
uitextattributetextshadowcolor: [uicolorwhitecolor],
uitextattributetextshadowoffset: [nsvaluevaluewithcgsize:cgsizemake(1, 1)]};
[appearance settitletextattributes:textattributes forstate:1];//forstate为0时为下正常状态，为1时为点击状态。
//修改leftbarbutton，rightbarbutton背景效果
[appearance setbackgroundimage:[uiimage imagenamed:@navbarbutton.png]
forstate:uicontrolstatenormal
style:uibarbuttonitemstylebordered
barmetrics:uibarmetricsdefault];
[appearance setbackgroundimage:[uiimage imagenamed:@navbarbutton_a.png]
forstate:uicontrolstatehighlighted
style:uibarbuttonitemstylebordered
barmetrics:uibarmetricsdefault];
//backbarbutton需要单独设置背景效果。只能在ios6.0以后才能用
[appearance setbackbuttonbackgroundimage:[uiimage imagenamed:@nav_bg.png]
forstate:0
barmetrics:uibarmetricsdefault];
[appearance setbackbuttonbackgroundimage:[uiimage imagenamed:@work.png]
forstate:1
barmetrics:uibarmetricsdefault];
[appearance setbackbuttontitlepositionadjustment:uioffsetmake(2, -1)
forbarmetrics:uibarmetricsdefault];
5.工具栏（uitoolbar）
uitoolbar *appearance = [uitoolbar appearance];
//样式和背景二选一即可，看需求了
//样式（黑色半透明，不透明等）设置
[appearance setbarstyle:uibarstyleblacktranslucent];
//背景设置
[appearance setbackgroundimage:[uiimage imagenamed:@toolbarbg.png]
fortoolbarposition:uitoolbarpositionany
barmetrics:uibarmetricsdefault];
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