【原】iOS学习之苹果原生代码实现Autolayout和VFL语言

1、添加约束的规则

  • 在创建约束之后,需要将其添加到作用的view上
  • 在添加时要注意目标view需要遵循以下规则:
  1)对于 两个同层级view之间 的约束关系,添加到它们的父view上  

  2)对于 两个不同层级view之间 的约束关系,添加到他们最近的共同父view上
  3)对于 有层次关系的两个view之间 的约束关系,添加到层次较高的父view上
 
2、苹果原生代码实现Autolayout
  • 步骤

  1)利用NSLayoutConstraint类创建具体的约束对象

   1> 一个NSLayoutConstraint对象就代表一个约束

   2> 创建约束对象的常用方法      

+(id)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(id)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c;

   参数说明

    pview1 :要约束的控件

      pattr1 :约束的类型(做怎样的约束)

      prelation :与参照控件之间的关系

      pview2 :参照的控件

      pattr2 :约束的类型(做怎样的约束)

      pmultiplier :乘数

      pc :常量

  2)添加约束对象到相应的view上

    - (void)addConstraint:(NSLayoutConstraint *)constraint;

    - (void)addConstraints:(NSArray *)constraints;

  • 注意点

  1)要先禁止autoresizing功能,设置view的下面属性为NO

   view.translatesAutoresizingMaskIntoConstraints = NO;

   如果不设置为NO,系统会自动将AutoresizingMask转为Autolayout的约束,从而造成约束冲突,控制台打印内容如下:

Unable to simultaneously satisfy constraints.

Probably at least one of the constraints in the following list is one you don't want. 

Try this: 

(1) look at each constraint and try to figure out which you don't expect; 

(2) find the code that added the unwanted constraint or constraints and fix it. 

(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 

(

    "<NSAutoresizingMaskLayoutConstraint:0x7ff339620540 h=--& v=--& V:[UIView:0x7ff339714510(0)]>",

    "<NSLayoutConstraint:0x7ff339714990 V:[UIView:0x7ff339714510(40)]>"

)

Will attempt to recover by breaking constraint 

<NSLayoutConstraint:0x7ff339714990 V:[UIView:0x7ff339714510(40)]>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.

The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

 

  2)添加约束之前,一定要保证相关控件都已经在各自的父控件上,也就是将子控件添加到父控件上

  3)不用再给view设置frame

  • 代码: 
   UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];// 添加宽度约束:100
    
    /************************** 蓝色 **************************/
    // 添加高度约束:40
    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0 constant:40];
    [blueView addConstraint:heightConstraint];
    
    // 添加左边约束:blueView的左边距离父控件左边有20的间距
    NSLayoutConstraint *leftConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:20];
    [self.view addConstraint:leftConstraint];
    
    // 添加右边约束:blueView的右边距离父控件右边有20的间距
    NSLayoutConstraint *rightConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:-20];
    [self.view addConstraint:rightConstraint];
    
    // 添加顶部约束:blueView的顶部距离父控件顶部有20的间距
    NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:20];
    [self.view addConstraint:topConstraint];
    
    /************************** 红色 **************************/
    // 添加高度约束:蓝色等高
    NSLayoutConstraint *heightConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0];
    [self.view addConstraint:heightConstraint2];
    
    // 添加左边约束:redView的左边 == 父控件的中心x
    NSLayoutConstraint *leftConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0];
    [self.view addConstraint:leftConstraint2];
    
    // 添加顶部约束:redView的顶部距离blueView的底部有20的间距
    NSLayoutConstraint *topConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:20];
    [self.view addConstraint:topConstraint2];
    
    // 添加右边约束:redView的右边 == blueView的右边
    NSLayoutConstraint *rightConstraint2 = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeRight multiplier:1.0 constant:0];
    [self.view addConstraint:rightConstraint2];

     效果图如下:

3、VFL语言

  • 什么是VFL语言

  VFL全称是Visual Format Language,翻译过来是“可视化格式语言”

  VFL是苹果公司为了简化Autolayout的编码而推出的抽象语言

  • VFL示例:

  1)H:[cancelButton(72)]-12-[acceptButton(50)]

  canelButton宽72,acceptButton宽50,它们之间间距12

  2)H:[wideView(>=60@700)]

  wideView宽度大于等于60point,该约束条件优先级为700(优先级最大值为1000,优先级越高的约束越先被满足)

  3)V:[redBox][yellowBox(==redBox)]

  竖直方向上,先有一个redBox,其下方紧接一个高度等于redBox高度的yellowBox

  4)H:|-10-[Find]-[FindNext]-[FindField(>=20)]

  水平方向上,Find距离父view左边缘默认间隔宽度,之后是FindNext距离Find间隔默认宽度;再之后是宽度不小于20的FindField,它和FindNext以及父view右边缘的间距都是默认宽度。(竖线“|” 表示superview的边缘)

  • VFL的使用

  1)使用VFL来创建约束数组方法

+ (NSArray *)constraintsWithVisualFormat:(NSString *)format options:(NSLayoutFormatOptions)opts metrics:(NSDictionary *)metrics views:(NSDictionary *)views;
   format :VFL语句
   opts :约束类型
   metrics :VFL语句中用到的具体数值
   views :VFL语句中用到的控件

  2)创建一个字典(内部包含VFL语句中用到的控件)的快捷宏定义

   NSDictionaryOfVariableBindings(...)

   代码:NSDictionaryOfVariableBindings(v1, v2, v3) 和 [NSDictionary dictionaryWithObjectsAndKeys:v1, @"v1", v2, @"v2", v3, @"v3", nil] 是等价的

  • 代码:
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    // 不要将AutoresizingMask转为Autolayout的约束
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    
    // 间距
    NSNumber *margin = @20;
    
    // 添加水平方向的约束
    NSString *vfl = @"H:|-margin-[blueView]-margin-[redView(==blueView)]-margin-|";
    NSDictionary *views = NSDictionaryOfVariableBindings(blueView, redView);
    NSDictionary *mertrics = NSDictionaryOfVariableBindings(margin);
    NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:vfl options:NSLayoutFormatAlignAllTop | NSLayoutFormatAlignAllBottom metrics:mertrics views:views];
    [self.view addConstraints:constraints];
    
    // 添加竖直方向的间距
    NSNumber *height = @40;
    NSString *vfl2 = @"V:[blueView(height)]-margin-|";
    NSDictionary *mertrics2 = NSDictionaryOfVariableBindings(margin, height);
    NSArray *constraints2 = [NSLayoutConstraint constraintsWithVisualFormat:vfl2 options:kNilOptions metrics:mertrics2 views:views];
    [self.view addConstraints:constraints2];

  效果图如下:

  

   VFL存在一定的缺陷,它只能满足大部分的约束,不能满足存在倍数关系的约束!

 

 

posted @ 2016-08-26 19:45  墨隐于非  阅读(537)  评论(0编辑  收藏  举报