Masonry 原理一

Under the hood Auto Layout is a powerful and flexible way of organising and laying out your views. However creating constraints from code is verbose and not very descriptive. Imagine a simple example in which you want to have a view fill its superview but inset by 10 pixels on every side

UIView *superview = self.view;

UIView *view1 = [[UIView alloc] init];

view1.translatesAutoresizingMaskIntoConstraints = NO;

view1.backgroundColor = [UIColor greenColor];

[superview addSubview:view1];

UIEdgeInsets padding = UIEdgeInsetsMake(10, 10, 10, 10);

[superview addConstraints:@[

    //view1 constraints

    [NSLayoutConstraint constraintWithItem:view1

                                 attribute:NSLayoutAttributeTop

                                 relatedBy:NSLayoutRelationEqual

                                    toItem:superview

                                 attribute:NSLayoutAttributeTop

                                multiplier:1.0

                                  constant:padding.top],

    [NSLayoutConstraint constraintWithItem:view1

                                 attribute:NSLayoutAttributeLeft

                                 relatedBy:NSLayoutRelationEqual

                                    toItem:superview

                                 attribute:NSLayoutAttributeLeft

                                multiplier:1.0

                                  constant:padding.left],

    [NSLayoutConstraint constraintWithItem:view1

                                 attribute:NSLayoutAttributeBottom

                                 relatedBy:NSLayoutRelationEqual

                                    toItem:superview

                                 attribute:NSLayoutAttributeBottom

                                multiplier:1.0

                                  constant:-padding.bottom],

    [NSLayoutConstraint constraintWithItem:view1

                                 attribute:NSLayoutAttributeRight

                                 relatedBy:NSLayoutRelationEqual

                                    toItem:superview

                                 attribute:NSLayoutAttributeRight

                                multiplier:1

                                  constant:-padding.right],

 ]];

Even with such a simple example the code needed is quite verbose and quickly becomes unreadable when you have more than 2 or 3 views. Another option is to use Visual Format Language (VFL), which is a bit less long winded. However the ASCII type syntax has its own pitfalls and its also a bit harder to animate as NSLayoutConstraint constraintsWithVisualFormat: returns an array.

Prepare to meet your Maker!

Heres the same constraints created using MASConstraintMaker

UIEdgeInsets padding = UIEdgeInsetsMake(10, 10, 10, 10);

[view1 mas_makeConstraints:^(MASConstraintMaker *make) {

    make.top.equalTo(superview.mas_top).with.offset(padding.top); //with is an optional semantic filler

    make.left.equalTo(superview.mas_left).with.offset(padding.left);

    make.bottom.equalTo(superview.mas_bottom).with.offset(-padding.bottom);

    make.right.equalTo(superview.mas_right).with.offset(-padding.right);

}];

巴特西

Masonry 原理一

Prepare to meet your Maker!

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