iOS 8UIAlertcontroller如何实现 message左对齐 ，title居中显示

实例化alertcontroller之后，可以遍历view的子视图，子视图title和message嵌套了多层父视图，（需要遍历6层subViews），

下面是取title和message的父视图的代码：

UIView *subView1 = alert.view.subviews[0];

UIView *subView2 = subView1.subviews[0];

UIView*subView3 = subView2.subviews[0];

UIView*subView4 = subView3.subviews[0];

UIView*subView5 = subView4.subviews[0];

取title和message：

UILabel*title = subView5.subviews[0];

UILabel*message = subView5.subviews[1];

然后设置message内容居左：

message.textAlignment = NSTextAlignmentLeft;

swift版：

let alert =UIAlertController(title:"版本升级", message: message,preferredStyle: .Alert)

let subView = alert.view.subviews[0].subviews[0].subviews[0].subviews[0].subviews[0]

let msgLabel = subView.subviews[1]as?UILabel

msgLabel?.textAlignment= .Left