ios通过按钮点击异步加载图片

#import <Foundation/Foundation.h>
#import "StringUtils.h"

@interface ImageManager : NSObject
{
  NSMutableDictionary *_imageDict;
  NSMutableArray *_imageArr;
}

@property(nonatomic, strong) NSString *httpUrl;
@property(nonatomic, strong) NSMutableDictionary *imageDict;

@property(nonatomic, assign) dispatch_queue_t networkQueue;

+ (ImageManager *) sharedInstance;


- (void)asyncImage:(NSString *)imageName imageView:(UIImageView *)imageView;
//插队
- (void)asyncImageInsert:(NSString *)imageName imageView:(UIImageView *)imageView insert:(BOOL)insert;
//不要在下载之前的数据
- (void)asyncImageCleanOld:(NSString *)imageName imageView:(UIImageView *)imageView cleanOld:(BOOL)cleanOld;

@end

//
// ImageManager.m
// myb-ios
//
// Created by warrior gao on 13-6-5.
// Copyright (c) 2013年 51myb. All rights reserved.
//

#import "ImageManager.h"

@interface ImageManager()

@end

@implementation ImageManager

//缓存图片的最大数量
static int counter = 0;

@synthesize imageDict = _imageDict;

//Singleton 
+ (ImageManager *)sharedInstance
{
  static id instance;
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    instance = self.new;
  });
  return instance;
}

- (id)init
{
  if((self = [super init]))
  {
    self.networkQueue = dispatch_queue_create("com.warrior.network.image", nil);
    _imageDict = [[NSMutableDictionary alloc] init];
    _imageArr = [[NSMutableArray alloc] init];
  }
  return self;
}

- (NSString *) fileFullPath:(NSString *)fileName
{
  NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0];
  
  NSString *fileFullPath = [NSString stringWithFormat:@"%@/%@",cachePath,fileName];
  
  return fileFullPath;
}

//不要在下载之前的数据
- (void)asyncImageCleanOld:(NSString *)imageName imageView:(UIImageView *)imageView cleanOld:(BOOL)cleanOld
{
  if(cleanOld)
  {
    [_imageArr removeAllObjects];
  }
  
  [self asyncImage:imageName imageView:imageView];
}

//插队，优先
- (void)asyncImageInsert:(NSString *)imageName imageView:(UIImageView *)imageView insert:(BOOL)insert
{
  if([StringUtils isEmpty:imageName]){
    return;
  }
  
  NSData *data = [NSData dataWithContentsOfFile:[self fileFullPath:[imageName stringByReplacingOccurrencesOfString:@"/" withString:@"-"]]];
  if(data == nil){
    [_imageDict setValue:imageView forKey:imageName];
    if(insert)
    {
      [_imageArr insertObject:imageName atIndex:0];
    }
    else
    {
      [_imageArr addObject:imageName];
    }
    
    [self cacheImage];
  } else {
    [imageView setImage:[UIImage imageWithData:data]];
  }
}

//正常，附加到后面
- (void)asyncImage:(NSString *)imageName imageView:(UIImageView *)imageView
{
  [self asyncImageInsert:imageName imageView:imageView insert:NO];
}

//异步缓存图片到本地，最多有两个线程
-(void)cacheImage
{
  for (; counter < 2 && _imageArr.count > 0; counter++)
  {
    NSString *imageName = nil;
    @synchronized(self){
      imageName = [[_imageArr objectAtIndex:0] copy];
      [_imageArr removeObjectAtIndex:0];
    }
    
    if(imageName == nil) continue;
    
    dispatch_async(self.networkQueue, ^{
      
      NSLog(@"Starting: %@", imageName);
      UIImage *avatarImage = nil;
      NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@",self.httpUrl, imageName]];
      NSData *responseData = [NSData dataWithContentsOfURL:url];
      if(responseData.length > 0)
      {
        [responseData writeToFile:[self fileFullPath:[imageName stringByReplacingOccurrencesOfString:@"/" withString:@"-"]] atomically:NO];
        avatarImage = [UIImage imageWithData:responseData];
        NSLog(@"Finishing: %@", imageName);
        
        if (avatarImage) {
          dispatch_async(dispatch_get_main_queue(), ^{
            UIImageView *imageView = [_imageDict objectForKey:imageName];
            if(imageView != nil && avatarImage != nil){
              [imageView setImage:avatarImage];
            }
            
            [_imageDict removeObjectForKey:imageName];
            [imageName release];
          });
        }
      }
      counter--;
      [self cacheImage];
    });
    
  }
}

@end