无论做什么，衡量标准是有没有给自己长本事

• pannel (noun)

piece of something ,a flat piece of wood with straight sides,which forms part of a door

a stained glass panel

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• 设置tabbar样式的时候，设置的是tabbar controllers子控制器的tabbarItem属性，可以是普通VC，也可以是navigation controller

• 每一个普通view controller初始化的时候都会初始化一个 tabbar item对象，但是属性是空的

• NSObject initialize

initialize the class before it receives its first message

+ (void)initialize;

• the runtime sends initialize to each class in a program just before the class is sent its first message from within the program,super class receive this message before their subclasses.
• initialize is invoked only once per class.if you want to perform independent initialization for the class,you should implement LOAD method.

• 设置导航栏的返回按钮

用外观类方法把bar对象拿出来，设置bar的外观，bar有一个backindicator属性，两个image都设置以后，就可以把导航栏的返回按钮初始化好

• 用masonry平分布局的思想

view1的上左下等于容器，view2的上下，宽度等于view1，view2的左边等于view1的右边，以此类推，lastView的右边等于容器的左边，这样，masonry就会自动平分view的宽度

• 为什么block里面不建议使用下划线变量 _property

因为 _property 等于 self -> _property,隐式表达了self，容易造成循环引用

• 设置tabbar 文字的颜色在当前控制器的tabbarItem上进行设置

[viewcontroller.tabBarItem setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor whiteColor]} forState:UIControlStateNormal];