学伴分析(二)UITableView优化

在这里主要处理这样一种情况:
后台请求数据返回后，在cell上显示一张与手机屏幕等宽的图片，高度根据比例换算，但是图片大小后台是不给的。也就是说图片的大小只能等图片异步加载完后才能确定，进而才能确定cell的高度

思路:
1.给图片默认的高度，同时用一个可变数组来管理这些图片的高度
2.等图片异步加载完后计算图片的高度存入数组中，同时在主线程中重新加载tableView

#import "TableViewController.h"
#import "DBTableViewCell.h"
#import "UIImageView+WebCache.h"
#import "UIColor+expanded.h"

@interface TableViewController ()
@property (nonatomic, strong) NSMutableArray *heightMArray;/** cell高度数组*/
@property (nonatomic, strong) NSMutableArray *newsMArray;  /** 新闻数据源*/
@end

@implementation TableViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tableView.backgroundColor = [UIColor colorWithHexString:@"f5f5f5"];
    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
    self.tableView.showsVerticalScrollIndicator = NO;
    [self.tableView registerClass:[DBTableViewCell class] forCellReuseIdentifier:NSStringFromClass([DBTableViewCell class])];
    //...获取网络数据, 在这里用假数据
    self.newsMArray = [[NSMutableArray alloc] initWithObjects:
@"http://pic2.zhimg.com/0e7f5548fca3cb7c29d69189c609f66d.jpg",
@"http://i0.hdslb.com/bfs/archive/b947b06dfb53af2bda5a53d145934596d5abbab5.jpg",
@"http://pic1.zhimg.com/3a0b66018f28365e57cc51816cb17678.jpg",
@"http://i0.hdslb.com/bfs/archive/c0f647ee5d5d77263fdbc49129563004e40b704e.jpg",
@"http://pic1.zhimg.com/e1ac4a1d20226abb980244537bf537f8.jpg",
@"http://i0.hdslb.com/bfs/archive/9b7e61ceb18aed36138e7726afcebbf69b6862e6.jpg",
@"http://pic2.zhimg.com/5e2f62618ca4bdd8fe4c38ed1ed69271.jpg",
@"http://i0.hdslb.com/bfs/archive/232dd1d0e577b9830386f7a3237de4a3e837c021.jpg",
@"http://pic3.zhimg.com/9e9c66ff2242006a573d37334b35b746.jpg",
@"http://i0.hdslb.com/bfs/archive/ced5cbdd59ce9b751a60472181faf3a6b2b73de8.jpg",
@"http://pic3.zhimg.com/9e9c66ff2242006a573d37334b35b746.jpg",
@"http://i0.hdslb.com/bfs/archive/0c819a923a0e816961ea8d5483584b4b503827c8.jpg",
@"http://pic3.zhimg.com/9caa7d6525ed9df0b505dffcf96a67c6.jpg", nil];
    [self.tableView reloadData];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - UITableViewDataSourse
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return self.newsMArray.count;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return 1;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    DBTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:NSStringFromClass([DBTableViewCell class])];
    cell.imageViewHeight = [self.heightMArray objectAtIndex:indexPath.section];
    [cell configWithDict:[self.newsMArray objectAtIndex:indexPath.section]];
    [cell.newsImageView sd_setImageWithURL:[NSURL URLWithString:[self.newsMArray objectAtIndex:indexPath.section]] placeholderImage:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
        // ------if用来判断是否已经update高度数组中图片的高度，如果没有if会陷入死循环
        if ([[self.heightMArray objectAtIndex:indexPath.section] isEqual:@(self.view.frame.size.width*3/5)]) {
            NSNumber *number = [NSNumber numberWithFloat:(image.size.height/image.size.width) * self.view.frame.size.width];
            [self.heightMArray replaceObjectAtIndex:indexPath.section withObject:number];
            // ------在主线程中重新加载tableView
            dispatch_async(dispatch_get_main_queue(), ^{
                [self.tableView reloadData];
            });
        }
    }];
    return cell;
}

#pragma mark - UITableViewDelegate
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
    return 10.0f;
}

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
    UIView *view = [UIView new];
    view.backgroundColor = [UIColor colorWithHexString:@"f5f5f5"];
    return view;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    // ------图片距离cell顶部5+底部5
    return 10 + [[self.heightMArray objectAtIndex:indexPath.section] floatValue];
}

#pragma mark - getter and setter
- (NSMutableArray *)heightMArray {
    if (_heightMArray == nil) {
        _heightMArray = [[NSMutableArray alloc] init];
        for (NSInteger i = 0; i < self.newsMArray.count; i++) {
            // ------给图片一个默认高度
            [_heightMArray addObject:@(self.view.frame.size.width*3/5)];
        }
    }
    return _heightMArray;
}
@end

完整版demo地址