iOS适配

1.各屏幕大小

2.Autolayout

（1）代码实现Autolayout的步骤
利用NSLayoutConstraint类创建具体的约束对象
添加约束对象到相应的view上
- (void)addConstraint:(NSLayoutConstraint *)constraint;
- (void)addConstraints:(NSArray *)constraints;

（2）代码实现Autolayout的注意点
要先禁止autoresizing功能，设置view的下面属性为NO
view.translatesAutoresizingMaskIntoConstraints = NO;
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
不用再给view设置frame

注意点：

对于两个同层级view之间的约束关系，添加到它们的父view上

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

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

    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];

3.Masonry

// 蓝色控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    [self.view addSubview:blueView];

    // 红色控件
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    [self.view addSubview:redView];

    // 添加约束
    CGFloat margin = 20;
    CGFloat height = 50;
    [blueView makeConstraints:^(MASConstraintMaker *make) {
        make.left.equalTo(self.view.left).offset(margin);
        make.right.equalTo(redView.left).offset(-margin);
        make.bottom.equalTo(self.view.bottom).offset(-margin);
        make.height.equalTo(height);
        make.top.equalTo(redView.top);
        make.bottom.equalTo(redView.bottom);
        make.width.equalTo(redView.width);
    }];

    [redView makeConstraints:^(MASConstraintMaker *make) {
        make.right.equalTo(self.view.right).offset(-margin);
    }];

/**
 mas_equalTo：这个方法会对参数进行包装
 equalTo：这个方法不会对参数进行包装
 mas_equalTo的功能强于 > equalTo
 */

/**
 约束的类型：
 1.尺寸：width\height\size
 2.边界：left\leading\right\trailing\top\bottom
 3.中心点：center\centerX\centerY
 4.边界：edges
 */

/*
// 这个方法只会添加新的约束
  [blueView mas_makeConstraints:^(MASConstraintMaker *make) {

  }];

 // 这个方法会将以前的所有约束删掉，添加新的约束
 [blueView mas_remakeConstraints:^(MASConstraintMaker *make) {

 }];

 // 这个方法将会覆盖以前的某些特定的约束
 [blueView mas_updateConstraints:^(MASConstraintMaker *make) {

 }];
 */