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  • 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);
    }];
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  • 原文地址:https://www.cnblogs.com/feng9exe/p/7929107.html
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