加载图像异步

Question

什么是超极简单的方式来加载在的UITableViewCell图像异步说给予IMAGEURL而无需子类的UITableViewCell，即：标准的UITableViewCell

Answer 1

我知道的最简单的方法是使用SDWebImage库。这是一个链接，介绍如何利用SDWebImage库异步加载头像。

SDWebImage是ImageView的扩展。下面是用法：

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

，这里是引用的文章：

Implementing Twitter Search

Answer 2

你可以使用一个线程。将按钮放在字典上。使用该线程。然后在方法setImage：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]; 

Answer 3

在您的m，包括客观的C运行时：

#import <objc/runtime.h> 

在顶部你的@implementation部分，定义一个静态常量以供使用：

static char * const myIndexPathAssociationKey = ""; 

在你的cellForRowAtIndexPath，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，支持最佳性能时，旧设备快速滚动，您可能想先......对于加载最近请求的图像，看this thread for asynchronously loading cell images using a last-in first-out stack and GCD。