ios - UITableViewCell imageview 滚动时消失

Question

我一直在尝试从我的网络服务器加载带有照片的表格 View 。我正在异步加载它们，并在这样做时在各个单元格中显示一个加载微调器。那部分工作得很好，但是当我滚动并且单元格被刷新时，图像消失了，但是其他单元格数据被正确加载。有趣的是，当我点击单元格时，图像突然出现了!它也是正确的图像。

有人知道发生了什么事以及可能如何解决它吗？

代码如下:

//
//  GalleryViewController.m
//  Photo
//
//  Created by Thomas on 5/8/14.
//  Copyright (c) 2014 Teilmann. All rights reserved.
//

#import "GalleryViewController.h"
#import "DBHandler.h"
#import "PListHandler.h"

@interface GalleryViewController ()

@end

@implementation GalleryViewController

#define kBgQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

@synthesize nsarray, gallery;

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor colorWithRed: 0.9333 green:0.3451 blue:0.08234 alpha:1.0];

    PListHandler *userinfo = [[PListHandler alloc] initWithPlistID:@"userinfo"];
    _dbhandler = [[DBHandler alloc] init];
    NSMutableArray *test = [_dbhandler getGalleryByUserID:[userinfo getUserID]];
    gallery = [NSArray arrayWithArray:test];
    NSLog(@"test: %@", test);

}

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

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{

    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

    // Return the number of rows in the section.
    return [gallery count];
}

-(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section{
    return @"My Gallery";
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"defaultcell" forIndexPath:indexPath];
    if(cell == nil){
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"defaultcell"];
    }

    cell.imageView.image = nil;
    UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleWhiteLarge];
    spinner.center = CGPointMake(160, 47);
    [spinner startAnimating];
    [cell.contentView addSubview:spinner];

    //hide labels until done loading
    cell.textLabel.hidden = YES;
    cell.detailTextLabel.hidden = YES;

    //download cell content async and display loading indicator in cells.
    dispatch_async(kBgQueue, ^{
        NSString *profilePicName = [NSString stringWithFormat:@"%@%@", [self.dbhandler getPicturesPath], [[gallery objectAtIndex:indexPath.row] valueForKey: @"filename"]];
        NSURL *profilepicurl = [NSURL URLWithString:profilePicName];
        NSData *imgData = [NSData dataWithContentsOfURL:profilepicurl];
        if(imgData){
            UIImage *icon = [UIImage imageWithData: imgData];
            if(icon){
                dispatch_async(dispatch_get_main_queue(), ^{
                    UITableViewCell *updateCell = (id)[tableView cellForRowAtIndexPath:indexPath];
                    if(updateCell){
                        NSLog(@"hej");
                        [updateCell.imageView setImage: icon];
                        updateCell.imageView.hidden = NO;
                        NSString *subtitle = [NSString stringWithFormat:@"Comments:  %@ \nPosted:        %@", [[gallery objectAtIndex:indexPath.row] valueForKey:@"comments"], [[gallery objectAtIndex:indexPath.row] valueForKey:@"created_at"]];

                        cell.detailTextLabel.numberOfLines = 0;
                        cell.textLabel.text = [NSString stringWithFormat:@"Votes:    %@",[[gallery objectAtIndex:indexPath.row] valueForKey:@"votes"]];
                        cell.detailTextLabel.text = subtitle;

                        //Stop spinner and make labels visible
                        [spinner stopAnimating];
                        cell.textLabel.hidden = NO;
                        cell.detailTextLabel.hidden = NO;
                    }
                });
            }
        }
    });

    return cell;
}


@end

Answer 1

我认为你的问题是每次显示单元格时你都在加载图像，请记住，你正在重用单元格 View 。

我用过 https://github.com/rs/SDWebImage它有一种方法来缓存图像并显示占位符。

[cell.imageView setImageWithURL:[NSURL URLWithString:@"http://www.domain.com/path/to/image.jpg"]
                   placeholderImage:[UIImage imageNamed:@"placeholder.png"]];