UITableView 布局在 push segue 和 return 上搞砸了. (iOS 8、Xcode beta 5、Swift)

这种行为的问题是，当你按下一个segue时，tableView将调用estimatedHeightForRowAtIndexPath来显示可见单元格，并将单元格高度重置为默认值.这发生在viewWillDisappear电话之后.如果你回到TableView，所有可见的单元格都被弄乱了..

我用estimatedCellHeightCache解决了这个问题.我只是简单地将这段代码添加到cellForRowAtIndexPath方法中:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    ...
    // put estimated cell height in cache if needed
    if (![self isEstimatedRowHeightInCache:indexPath]) {
        CGSize cellSize = [cell systemLayoutSizeFittingSize:CGSizeMake(self.view.frame.size.width, 0) withHorizontalFittingPriority:1000.0 verticalFittingPriority:50.0];
        [self putEstimatedCellHeightToCache:indexPath height:cellSize.height];
    }
    ...
}

现在，您必须按照以下步骤实施estimatedHeightForRowAtIndexPath:

-(CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return [self getEstimatedCellHeightFromCache:indexPath defaultHeight:41.5];
}

Configure the Cache

将此属性添加到您的.h文件:

@property NSMutableDictionary *estimatedRowHeightCache;

实施放置/获取/重置的方法..缓存:

#pragma mark - estimated height cache methods

// put height to cache
- (void) putEstimatedCellHeightToCache:(NSIndexPath *) indexPath height:(CGFloat) height {
    [self initEstimatedRowHeightCacheIfNeeded];
    [self.estimatedRowHeightCache setValue:[[NSNumber alloc] initWithFloat:height] forKey:[NSString stringWithFormat:@"%d", indexPath.row]];
}

// get height from cache
- (CGFloat) getEstimatedCellHeightFromCache:(NSIndexPath *) indexPath defaultHeight:(CGFloat) defaultHeight {
    [self initEstimatedRowHeightCacheIfNeeded];
    NSNumber *estimatedHeight = [self.estimatedRowHeightCache valueForKey:[NSString stringWithFormat:@"%d", indexPath.row]];
    if (estimatedHeight != nil) {
        //NSLog(@"cached: %f", [estimatedHeight floatValue]);
        return [estimatedHeight floatValue];
    }
    //NSLog(@"not cached: %f", defaultHeight);
    return defaultHeight;
}

// check if height is on cache
- (BOOL) isEstimatedRowHeightInCache:(NSIndexPath *) indexPath {
    if ([self getEstimatedCellHeightFromCache:indexPath defaultHeight:0] > 0) {
        return YES;
    }
    return NO;
}

// init cache
-(void) initEstimatedRowHeightCacheIfNeeded {
    if (self.estimatedRowHeightCache == nil) {
        self.estimatedRowHeightCache = [[NSMutableDictionary alloc] init];
    }
}

// custom [self.tableView reloadData]
-(void) tableViewReloadData {
    // clear cache on reload
    self.estimatedRowHeightCache = [[NSMutableDictionary alloc] init];
    [self.tableView reloadData];
}