ios Tableview行高的计算

NSDictionary *attrs = @{NSFontAttributeName : font};

[str boundingRectWithSize:size options:NSStringDrawingUsesLineFragmentOrigin attributes:attrs context:nil].size

_tableView.estimatedRowHeight = 30;
_tableView.rowHeight = UITableViewAutomaticDimension;

-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
NSString *identify = NSStringFromClass([Case8Cell class]);
Case8Cell *cell = [tableView dequeueReusableCellWithIdentifier:identify];
if (!cell) {
cell = [[Case8Cell alloc]initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:identify];
}
Case8DataEntity *entity = _arrayEntity[indexPath.row];
[cell setEntityData:entity indexPath:indexPath click:^() {

}];
//缓存行高
if (entity.cellHeight <= 0) {
entity.cellHeight = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height + 0.5f;
}
if (entity.cellHeight < 50) {
return 50;
}
return entity.cellHeight;
}