Question

在UITableViewCell中异步加载图像的超级简单方法是什么？假设给定一个imageURL而不必为UITableViewCell创建子类，即：标准UITableViewCell

Answer 1

我知道最简单的方法是使用SDWebImage库。这是一个链接，解释了如何利用SDWebImage库异步加载化身。

SDWebImage是ImageView的扩展。以下是用法：

// load the avatar using SDWebImage
    [cell.imageView setImageWithURL:[NSURL URLWithString:tweet.profileImageUrl]
                   placeholderImage:[UIImage imageNamed:@"grad_001.png"]];

以下是引用的文章：

Implementing Twitter Search

Answer 2

在.m中，包含目标c运行时：

#import <objc/runtime.h>

在@implementation部分的顶部，定义一个静态常量供以下使用：

static char * const myIndexPathAssociationKey = "";

在您的cellForRowAtIndexPath中，添加以下代码：

// Store a reference to the current cell that will enable the image to be associated with the correct  
// cell, when the image subsequently loaded asynchronously. Without this, the image may be mis-applied
// to a cell that has been dequeued and reused for other content, during rapid scrolling. 
objc_setAssociatedObject(cell,
                         myIndexPathAssociationKey,
                         indexPath,
                         OBJC_ASSOCIATION_RETAIN);

// Load the image on a high priority background queue using Grand Central Dispatch.
// Can change priority by replacing HIGH with DEFAULT or LOW if desired.
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(queue, ^{
    UIImage *image = ... // Obtain your image here.

    // Code to actually update the cell once the image is obtained must be run on the main queue.
    dispatch_async(dispatch_get_main_queue(), ^{
        NSIndexPath *cellIndexPath = (NSIndexPath *)objc_getAssociatedObject(cell, myIndexPathAssociationKey);
        if ([indexPath isEqual:cellIndexPath]) {
        // Only set cell image if the cell currently being displayed is the one that actually required this image.
        // Prevents reused cells from receiving images back from rendering that were requested for that cell in a previous life.
            [cell setImage:image];
        }
    });
}];

最后，为了在旧设备上快速滚动时支持最佳性能，您可能需要先加载最近请求的图片...为此，请参阅this thread for asynchronously loading cell images using a last-in first-out stack and GCD。

Answer 3

您可以使用线程。首先将按钮放在字典上。然后使用线程。最后在 setImage：方法中，您可以放置图像。

NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];

        [dictionary setObject:url forKey:@"url"];
        [dictionary setObject:image forKey:@"image"];
        [NSThread detachNewThreadSelector:@selector(setImage:) 
                                 toTarget:self 
                               withObject:dictionary];

异步加载UITableViewCell中的图像

3 个答案: