通过NSCache缓存已经算好的行高
@interface ZHCellHeightCalculator : NSObject //系统计算高度后缓存进cache
-(void)setHeight:(CGFloat)height withCalculateheightModel:(ZHCalculateHeightModel *)model; //根据model hash 获取cache中的高度,如过无则返回－1
-(CGFloat)heightForCalculateheightModel:(ZHCalculateHeightModel *)model; //清空cache
-(void)clearCaches; @end
#import "ZHCellHeightCalculator.h" @interface ZHCellHeightCalculator ()
@property (strong, nonatomic, readonly) NSCache *cache;
@end @implementation ZHCellHeightCalculator #pragma mark - Init
-(instancetype)init
{
self = [super init];
if (self) {
[self defaultConfigure];
}
return self;
} -(void)defaultConfigure
{
NSCache *cache = [NSCache new];
cache.name = @"ZHCellHeightCalculator.cache";
cache.countLimit = ;
_cache = cache; } #pragma mark - NSObject - (NSString *)description
{
return [NSString stringWithFormat:@"<%@: cache=%@",
[self class], self.cache];
} #pragma mark - Publci Methods
-(void)clearCaches
{
[self.cache removeAllObjects];
} -(void)setHeight:(CGFloat)height withCalculateheightModel:(ZHCalculateHeightModel *)model
{
NSAssert(model != nil, @"Cell Model can't nil");
NSAssert(height >= , @"cell height must greater than or equal to 0"); [self.cache setObject:[NSNumber numberWithFloat:height] forKey:@(model.hash)];
} -(CGFloat)heightForCalculateheightModel:(ZHCalculateHeightModel *)model
{
NSNumber *cellHeightNumber = [self.cache objectForKey:@(model.hash)];
if (cellHeightNumber) {
return [cellHeightNumber floatValue];
}else
return -; }
@end
使用方式：
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
ZHCalculateHeightModel *model = model = [dataArray objectAtIndex:indexPath.row]; CGFloat height = [heightCalculator heightForCalculateheightModel:model];
if (height>) {
NSLog(@"cache height");
return height;
}else{
NSLog(@"calculate height");
}
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------------------------------------*/ CGFloat cellHeight = fittingHeight+*/[UIScreen mainScreen].scale;//必须加上上下分割线的高度
[heightCalculator setHeight:cellHeight withCalculateheightModel:model];
return cellHeight;
}