Lazytableimages无法加载到自定义单元格故事板上

Question

我正在尝试在故事板中的自定义单元格中加载Lazy Tableview，但表格视图看起来只是空白：

这是源代码：

LazyLoadTable.m

#import "CellData.h"
#import "LazyLoadTableView.h"
#import "CustomCell.h"
#import "ParseOperation.h"
#import "ImageDownloader.h"
#define kCustomRowHeight    157
#define kCustomRowCount     1

static NSString *const xmlDataUrl =
@"http://itunes.apple.com/us/rss/topfreeapplications/limit=300/xml";

@interface LazyLoadTableView ()

@end

@implementation LazyLoadTableView
@synthesize tableElements;
@synthesize queue;
@synthesize connection;
@synthesize xmlData;
@synthesize tView;
@synthesize imageDownloadsInProgress;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization

        self.tableElements=[[NSMutableArray alloc] init];
        self.imageDownloadsInProgress = [NSMutableDictionary dictionary];



    }
    return self;
}


- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.


    self.title=@"Menu";
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:xmlDataUrl]];
    self.connection = [[NSURLConnection alloc] initWithRequest:urlRequest delegate:self];

    // Test the validity of the connection object.
    NSAssert(self.connection != nil, @"Failure to create URL connection.");

    // show in the status bar that network activity is starting
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

}


    - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
    {
        int count = [tableElements count];

        // ff there's no data yet, return enough rows to fill the screen
        if (count == 0)
        {
            return kCustomRowCount;
        }
        return count;
    }


    - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
    {
        // customize the appearance of table view cells


        static NSString *placeholderCellIdentifier = @"PlaceholderCell";

        // add a placeholder cell while waiting on table data
        int nodeCount = [self.tableElements count];

        if (nodeCount == 0 && indexPath.row == 0)
        {
            UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:placeholderCellIdentifier];
            if (cell == nil)
            {
                cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle
                                              reuseIdentifier:placeholderCellIdentifier];
                cell.detailTextLabel.textAlignment = NSTextAlignmentCenter ;
                cell.selectionStyle = UITableViewCellSelectionStyleNone;
            }

            cell.detailTextLabel.text = @"Loading…";

            return cell;
        }


        static NSString *CustomCellIdentifier = @"CustomCellIdentifier";




        CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:CustomCellIdentifier];
        if (cell == nil) {
            NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil];
            for (id oneObject in nib) if ([oneObject isKindOfClass:[CustomCell class]])
                cell = (CustomCell *) [nib objectAtIndex:0];
        }
        // Leave cells empty if there's no data yet
        if (nodeCount > 0)
        {
            // Set up the cell...
            CellData *cellData = (self.tableElements)[indexPath.row];

            cell.name.text = cellData.name;


            // Only load cached images; defer new downloads until scrolling ends
            if (!cellData.icon)
            {
                if (self.tView.dragging == NO && self.tView.decelerating == NO)
                {
                    [self startIconDownload:cellData forIndexPath:indexPath];
                }
                // if a download is deferred or in progress, return a placeholder image




                cell.itemImage.image = [UIImage imageNamed:@"Placeholder.png"];
            }
            else
            {
                cell.itemImage.image = cellData.icon;
            }

        }


        return cell;
    }

    - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
        return kCustomRowHeight;

    }




    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    self.xmlData = [NSMutableData data];    // start off with new data
}


- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.xmlData appendData:data];  // append incoming data
}
#pragma mark -
#pragma mark NSURLConnection delegate methods

- (void)handleError:(NSError *)error
{
    NSString *errorMessage = [error localizedDescription];
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Cannot Show Data"
                                                        message:errorMessage
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
    [alertView show];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

    if ([error code] == kCFURLErrorNotConnectedToInternet)
    {
        // if we can identify the error, we can present a more precise message to the user.
        NSDictionary *userInfo = @{NSLocalizedDescriptionKey: @"No Connection Error"};
        NSError *noConnectionError = [NSError errorWithDomain:NSCocoaErrorDomain
                                                         code:kCFURLErrorNotConnectedToInternet
                                                     userInfo:userInfo];
        [self handleError:noConnectionError];
    }
    else
    {
        // otherwise handle the error generically
        [self handleError:error];
    }

    self.connection = nil;   // release our connection
}


- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    self.connection = nil;   // release our connection

    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

    // create the queue to run our ParseOperation
    self.queue = [[NSOperationQueue alloc] init];
    ParseOperation *operation = [[ParseOperation alloc] initWithData:self.xmlData delegate:self];

    [queue addOperation:operation]; // this will start the "ParseOperation"



    self.xmlData = nil;
}
- (void)didFinishParsing:(NSArray *)cellDataList
{
    [self performSelectorOnMainThread:@selector(handleLoadedApps:) withObject:cellDataList waitUntilDone:NO];

    self.queue = nil;   // we are finished with the queue and our ParseOperation
}

- (void)parseErrorOccurred:(NSError *)error
{
    [self performSelectorOnMainThread:@selector(handleError:) withObject:error waitUntilDone:NO];
}
- (void)handleLoadedApps:(NSArray *)loadedCellData
{
    [self.tableElements addObjectsFromArray:loadedCellData];

    // tell our table view to reload its data, now that parsing has completed
    [self.tView reloadData];
}


// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return YES;
}

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


- (void)startIconDownload:(CellData *)cellData forIndexPath:(NSIndexPath *)indexPath
{
    ImageDownloader *imageDownloader = imageDownloadsInProgress[indexPath];
    if (imageDownloader == nil)
    {
        imageDownloader = [[ImageDownloader alloc] init];
        imageDownloader.cellData = cellData;
        imageDownloader.indexPathInTableView = indexPath;
        imageDownloader.delegate = self;
        imageDownloadsInProgress[indexPath] = imageDownloader;
        [imageDownloader startDownload];
    }
}

// this method is used in case the user scrolled into a set of cells that don't have their app icons yet
- (void)loadImagesForOnscreenRows
{
    if ([self.tableElements count] > 0)
    {
        NSArray *visiblePaths = [self.tView indexPathsForVisibleRows];
        for (NSIndexPath *indexPath in visiblePaths)
        {
            CellData *cellData = (self.tableElements)[indexPath.row];

            if (!cellData.icon) // avoid the app icon download if the app already has an icon
            {
                [self startIconDownload:cellData forIndexPath:indexPath];
            }
        }
    }
}

// called by our ImageDownloader when an icon is ready to be displayed
- (void)imageDidLoad:(NSIndexPath *)indexPath
{
    ImageDownloader *imageDownloader = imageDownloadsInProgress[indexPath];
    if (imageDownloader != nil)
    {
        CustomCell *cell = (CustomCell *)[self.tView cellForRowAtIndexPath:imageDownloader.indexPathInTableView];

        // Display the newly loaded image
        cell.itemImage.image = imageDownloader.cellData.icon;
    }
}


#pragma mark -
#pragma mark Deferred image loading (UIScrollViewDelegate)

// Load images for all onscreen rows when scrolling is finished
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
    if (!decelerate)
    {
        [self loadImagesForOnscreenRows];
    }
}

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



@end

CustomCell.m

#import "CustomCell.h"

@implementation CustomCell

@synthesize itemImage;

@synthesize name;


- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        // Initialization code
    }
    return self;
}

- (void)setSelected:(BOOL)selected animated:(BOOL)animated
{
    [super setSelected:selected animated:animated];

    // Configure the view for the selected state
}

@end

Answer 1

没有阅读所有代码，但看起来你试图延迟加载带有一些文字的图像。我强烈建议使用SDWebImage进行延迟加载。设置起来非常简单直接。