UIImage和UITableViewCell维度

简单的回答是:一旦你有了图像,那么image.size.height应该能满足你的需求。但是,在cellForRowAtIndexPath:之前调用heightForRowAtIndexPath:。所以您可能希望实现某种类型的异步映像加载程序。看看苹果的样品 LazyTableImages 完全实现这一点。

答案很长:我做了一些捷径来回答你的问题,而不需要写1000行代码,但这应该证明了我的想法。重要的位是cellForRowAtIndexPath:和heightForRowAtIndexPath:。

RootViewController.m

#import "RootViewController.h"

@interface RootViewController()
- (void)loadImagesForOnscreenRows;
- (void)loadImageForIndexPath:(NSIndexPath *)indexPath;
@end

@implementation RootViewController

static NSMutableDictionary *images;
static NSDictionary *pathAndName;

#pragma mark -
#pragma mark NSObject
- (void)dealloc {
    [images release];
    [pathAndName release];
    [super dealloc];
}


#pragma mark UIViewController
- (void)viewDidLoad {

    // image paths from WikiMedia
    pathAndName = [[NSDictionary alloc] initWithObjectsAndKeys:
                   @"http://upload.wikimedia.org/wikipedia/commons/8/89/Crystal_Clear_app_virus_detected_2.png", @"Big Virus",
                   @"http://upload.wikimedia.org/wikipedia/commons/thumb/c/c7/Crystal_Clear_app_virus_detected.png/64px-Crystal_Clear_app_virus_detected.png", @"Little Virus",
                   nil];

    images = [[NSMutableDictionary alloc] initWithCapacity:[pathAndName allKeys].count];
}

- (void)viewDidUnload {
    [images release];
    images = nil;

    [pathAndName release];
    pathAndName = nil;
}


#pragma mark UIScrollViewDelegate
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (!decelerate) {
        [self loadImagesForOnscreenRows];
    }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    [self loadImagesForOnscreenRows];
}


#pragma mark UITableViewDataSource
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [pathAndName allKeys].count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    // typical cell creation
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    // if the image is downloaded, then set the cell image.
    NSString *key = [[pathAndName allKeys] objectAtIndex:indexPath.row];
    UIImage *image = [images objectForKey:key];
    if (image) {
        [cell.imageView setImage:image];
    }

    [cell.textLabel setText:key];
    return cell;
}

#pragma mark UITableViewDelegate
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {

    NSString *key = [[pathAndName allKeys] objectAtIndex:indexPath.row];
    UIImage *image = [images objectForKey:key];
    if (image) {
        return image.size.height;
    }

    // if the image is not yet downloaded, kick off downloading it and return a default row height.
    [self performSelector:@selector(loadImageForIndexPath:) withObject:indexPath afterDelay:0.1f];
    return tableView.rowHeight;
}


#pragma mark -
#pragma mark RootViewController
#pragma mark Private Extension
- (void)loadImagesForOnscreenRows {
    NSArray *visiblePaths = [self.tableView indexPathsForVisibleRows];
    for (NSIndexPath *indexPath in visiblePaths) {
        [self loadImageForIndexPath:indexPath];
    }
}

// This is a big shortcut from the Apple sample, LazyTableImages.
- (void)loadImageForIndexPath:(NSIndexPath *)indexPath {

    NSString *key = [[pathAndName allKeys] objectAtIndex:indexPath.row];
    if ([images objectForKey:key]) return;

    NSString *path = [pathAndName objectForKey:key];

    NSError *error = nil;
    NSData *receivedData = [NSData dataWithContentsOfURL:[NSURL URLWithString:path] 
                                                 options:NSUncachedRead     
                                                   error: &error];
    if (error) return;

    UIImage *image = [[UIImage alloc] initWithData:receivedData];
    [images setObject:image forKey:key];
    [image release];
    NSArray *indexPaths = [NSArray arrayWithObject:indexPath];
    [self.tableView reloadRowsAtIndexPaths:indexPaths withRowAnimation:UITableViewRowAnimationFade];
}


@end