實(shí)現(xiàn)思路

1.使用autoLayout對(duì)collectionView進(jìn)行約束，對(duì)collationView的左、右、上、下進(jìn)行約束，不約束高度。
2.對(duì)collectionView的“contentSize”進(jìn)行監(jiān)聽，當(dāng)監(jiān)聽到其contentSize發(fā)生變化后，對(duì)collectionView重新進(jìn)行約束，并約束高度。
3.注意：在collectionView的數(shù)據(jù)源發(fā)生變化后需要對(duì)collectionView進(jìn)行reloadData，并且調(diào)用collectionView的layoutIfNeeded方法。

核心代碼

 [self.collectionView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.right.top.bottom.mas_equalTo(self);
    }];
[self.collectionView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:nil];

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context{
    if ([keyPath isEqualToString:@"contentSize"]) {
        CGFloat height = self.collectionView.contentSize.height;
        [self.collectionView mas_remakeConstraints:^(MASConstraintMaker *make) {
            make.left.right.top.bottom.mas_equalTo(self);
            make.height.equalTo(@(height));
        }];
    }
}

- (void)setDataArr:(NSArray *)dataArr{
    _dataArr = dataArr;
    [self.collectionView reloadData];
    [self.collectionView layoutIfNeeded];
}

demo地址：https://github.com/yangguanghei/DynamicTableView.git