使用代码实现autolayout

//|:表示父视图

//_:表示的是距离

//v:表示垂直方向

//H:表示水平方向

//>=:表示视图间距,宽度和高度必须大于或等于某个值

//<=:表示视图距离,宽度和高度必须小于或等于某个值

//==:表示视图间距,宽度或高度必须等于某个值

UIButton*button1 = [UIButtonbuttonWithType:UIButtonTypeSystem];

button1.backgroundColor= [UIColoryellowColor];

[button1setTitle:@"Click"forState:UIControlStateNormal];

[button1setTranslatesAutoresizingMaskIntoConstraints:NO];//标记是否自动布局

[self.viewaddSubview:button1];

UIButton*button2 = [UIButtonbuttonWithType:UIButtonTypeSystem];

[button2setBackgroundColor:[UIColorredColor]];

[button2setTitle:@"Click Me"forState:UIControlStateNormal];

[self.viewaddSubview:button2];

NSDictionary*views =NSDictionaryOfVariableBindings(button1, button2);

[self.viewaddConstraints:[NSLayoutConstraintconstraintsWithVisualFormat:@"H:|-(==50)-[button1(100)]"options:0metrics:nilviews:views]];