Detailed explanation of using masonry on scrollView in ios

Use a subview of scrollView to adjust contentSize

_scroll_Bg = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 100, SCREEN_W, 200)];
  _scroll_Bg.pagingEnabled = YES;
  _scroll_Bg.delegate = self;
  _scroll_Bg.backgroundColor = [UIColor redColor];
  [ addSubview:_scroll_Bg];

1. Now scrollView adds a main subview, size fits scrollView

UIView *bgView = [[UIView alloc] init];
   = [UIColor blueColor];
  [_scroll_Bg addSubview:bgView];
  [bgView mas_makeConstraints:^(MASConstraintMaker *make) {
    (_scroll_Bg).(UIEdgeInsetsZero);
    (_scroll_Bg);
  }];

2. After that, all subviews need to be added to this bgView

UIView *childV = [[UIView alloc] init];
   = [UIColor cyanColor];
  [bgView addSubview:childV];
  [childV mas_makeConstraints:^(MASConstraintMaker *make) {
    .mas_equalTo(0);
    .mas_equalTo(250);
    .mas_equalTo(1000);
  }];

3. The last subview added shall prevail, and then reconstrain the bgView.

[bgView mas_makeConstraints:^(MASConstraintMaker *make) {
    (childV.mas_bottom);
  }];

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