UIScrollView 约束

Created by 大刘 liuxing8807@126.com

关联:我的简书一篇文章 https://www.jianshu.com/p/29a2a4d840fd

以新建一和控制器的view同大的UIScrollView并垂直滚动为例:

代码布局约束示例

// Step 1> ScrollView上下左右为0
[scrollView mas_makeConstraints:^(MASConstraintMaker *make) {
    make.left.top.right.bottom.mas_equalTo(0);    
}];

// Step 2> 新建ContentView并加入ScrollView, 设置其上下左右，宽和ScrollView相同
UIView* contentView = UIView.new;
[self.scrollView addSubview:contentView];
    
[contentView mas_makeConstraints:^(MASConstraintMaker *make) {
    make.edges.equalTo(self.scrollView);
    make.width.equalTo(self.scrollView);
}];

// Step 3> 把各个子控制加入ContentView, 而不是ScrollView
UIView *view1 = UIView.new;
[contentView addSubview:view1];
...
UIView *view2 = UIView.new;
[contentView addSubview:view2];
...
UIView *lastSubView = UIView.new;
[contentView addSubview:lastSubView];
...

// Step 4> 使用最后一个subView控制contentView的高，从而控制scrollView的contentSize.height
- (void)resetContentViewConstraint:(UIView *)contentView withLastSubview:(UIView *)lastSubview {
    if (!contentView || !lastSubview) {
        return;
    }
    [contentView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.bottom.mas_equalTo(lastSubview.mas_bottom);
    }];
}

XIB布局约束示例

Step 1> 拖入ScrollView，设置其相对于控制器的View上下左右为0
Step 2> 拖入UIView放在ScrollView上作为ScrollView的ContentView并设置:
        contentView.left.top.right.bottom = 0; // relative to scrollView
        contentView.width = controller.view.width; 
        contentView.height = scrollView.height(此height即scrollView.contentSize.height，由于height不固定，因此勾选这个约束的Placeholder: Remove at build time，表示这个约束实际上通过代码控制，但先伪设置上以便XCode不作错误提示)
Step 4> 通过代码控制ContentView.height
- (void)resetContentViewConstraint:(UIView *)contentView withLastSubview:(UIView *)lastSubview {
    if (!contentView || !lastSubview) {
        return;
    }
    [contentView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.bottom.mas_equalTo(lastSubview.mas_bottom);
    }];
}
上面是设置bottom的方式来处理的，也可以直接设置contentView.height, 但一般不这么做