UITableViewCell 高度自适应

96
Show_Perry
2016.09.08 18:01* 字数 457

UITableViewCell 高度自适应一直是我们做动态Cell高度时遇到的最烦躁的问题,Cell动态高度计算可以去看看sunny的这篇文章介绍,今天主要和大家分享下我在使用systemLayoutSizeFittingSize系统自带方法计算高度的一些心得!

Demo gif

ZHAutoCalculateCellHeight.gif

先看原函数注释

/* The size fitting most closely to targetSize in which the receiver's subtree can be laid out while optimally satisfying the constraints. If you want the smallest possible size, pass UILayoutFittingCompressedSize; for the largest possible size, pass UILayoutFittingExpandedSize.
 Also see the comment for UILayoutPriorityFittingSizeLevel.
 */
- (CGSize)systemLayoutSizeFittingSize:(CGSize)targetSize NS_AVAILABLE_IOS(6_0); // Equivalent to sending -systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority: with UILayoutPriorityFittingSizeLevel for both priorities.

从注释中我们可以看出,当你的约束条件配置好后它可以计算出最接近目标的Size,那我们该如何下手呢?

1.首先我们需要建一个UITableViewCell

假如我们Cell的布局如下所示:

屏幕快照 2016-09-08 17.08.11.png

Cell所对应的Class我们取名为ZHCalculateTableViewCell
所带属性我们定义为:

@interface ZHCalculateTableViewCell : UITableViewCell
@property (weak, nonatomic) IBOutlet UILabel *TitleLabel;
@property (weak, nonatomic) IBOutlet UILabel *ContentLabel;
@property (weak, nonatomic) IBOutlet UIImageView *showImgView;
@property (weak, nonatomic) IBOutlet UILabel *UseNameLabel;
@property (weak, nonatomic) IBOutlet UILabel *TimeLabel;
@property (strong, nonatomic) ZHCalculateHeightModel *model;
@end

看到这里也许你会疑惑ZHCalculateHeightModel是什么,它是我们Cell所要展示的数据来源!

2.然后我们为我们的Cell建个数据模型

Cell的模型名称我们暂定为:ZHCalculateHeightModel
所带属性:

@interface ZHCalculateHeightModel : NSObject
@property (nonatomic, strong) NSString *title;
@property (nonatomic, strong) NSString *content;
@property (nonatomic, strong) NSString *username;
@property (nonatomic, strong) NSString *time;
@property (nonatomic, strong) NSString *imageName;

Ok,数据模型建立好了,展示的TableViewCell也有了, Just Show it~

3. 建一个继承于UITableViewControllerZHCustomLayoutTableViewController

  • 建一个在函数-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath中调用的Cell:
@property (nonatomic, strong)  ZHCalculateTableViewCell *prototypeCell;
  • 注册Cell
[self.tableView registerNib:[UINib nibWithNibName:@"ZHCalculateTableViewCell" bundle:[NSBundle mainBundle]] forCellReuseIdentifier:CellIdentifier];
self.tableView.estimatedRowHeight = 100;//很重要保障滑动流畅性
self.prototypeCell = [self.tableView dequeueReusableCellWithIdentifier:CellIdentifier];

  • 动态计算高度
  -(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{

    ZHCalculateTableViewCell *cell = self.prototypeCell;
    cell.contentView.translatesAutoresizingMaskIntoConstraints = NO;
    [self configureCell:cell atIndexPath:indexPath];//必须先对Cell中的数据进行配置使动态计算时能够知道根据Cell内容计算出合适的高度
    
    /*------------------------------重点这里必须加上contentView的宽度约束不然计算出来的高度不准确-------------------------------------*/
    CGFloat contentViewWidth = CGRectGetWidth(self.tableView.bounds);
    NSLayoutConstraint *widthFenceConstraint = [NSLayoutConstraint constraintWithItem:cell.contentView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:contentViewWidth];
    [cell.contentView addConstraint:widthFenceConstraint];
    // Auto layout engine does its math
    CGFloat fittingHeight = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
    [cell.contentView removeConstraint:widthFenceConstraint];
    /*-------------------------------End------------------------------------*/
    
    return fittingHeight+2*1/[UIScreen mainScreen].scale;//必须加上上下分割线的高度
}


#pragma mark Configure Cell Data
- (void)configureCell:(ZHCalculateTableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    cell.model = [dataArray objectAtIndex:indexPath.row];//Cell中对其进行处理
}

ZHCalculateTableViewCell Model的Set函数重写为

#pragma mark - Setters
-(void)setModel:(ZHCalculateHeightModel *)model
{
    _model = model;
    self.TitleLabel.text = model.title;
    self.ContentLabel.text = model.content;
    self.showImgView.image = model.imageName.length > 0 ? [UIImage imageNamed:model.imageName] : nil;
    self.UseNameLabel.text = model.username;
    self.TimeLabel.text = model.time;
    
}

扩展

我们可以在计算高度后对其进行缓存,下次可以直接返回!如何缓存可以看为UITableViewCell 高度自适应加速.

总结

  • -(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath一定不要用ZHCalculateTableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];来获取Cell。这里是因为[tableView cellForRowAtIndexPath:indexPath]会调用-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath导致进入死循环。
  • 上述动态计算Cell高度中最最重要的是需要在计算前先初始化Cell中的数据。
  • 一定要对ContentView加上宽度约束。
 CGFloat contentViewWidth = CGRectGetWidth(self.tableView.bounds);
    NSLayoutConstraint *widthFenceConstraint = [NSLayoutConstraint constraintWithItem:cell.contentView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:contentViewWidth];
    [cell.contentView addConstraint:widthFenceConstraint];
    // Auto layout engine does its math
    CGFloat fittingHeight = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
    [cell.contentView removeConstraint:widthFenceConstraint];

Demo 下载地址

GitHub

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