http图片不显示：
网上说加NSAllowsArbitraryLoads，现在看来应该是加入App Transport Security Settings，当然你如果加入NSAllowsArbitraryLoads会变成App Transport Security Settings，不罗嗦，直接添加图片过程。
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代码上跳：cmd+option+[
代码左移：cmd+[
代码右移：cmd+}
// ViewController.m// 06-掌握-多图片下载#import "ViewController.h"#import "XMGApp.h"@interface ViewController ()/** 所有数据 */@property (nonatomic, strong) NSArray *apps;/** 内存缓存的图片 */@property (nonatomic, strong) NSMutableDictionary *imageCache;@end@implementation ViewController- (NSMutableDictionary *)imageCache{ if (!_imageCache) { _imageCache = [NSMutableDictionary dictionary]; } return _imageCache;}- (NSArray *)apps{ if (!_apps) { NSArray *dictArray = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil]]; NSMutableArray *appArray = [NSMutableArray array]; for (NSDictionary *dict in dictArray) { [appArray addObject:[XMGApp appWithDict:dict]]; } _apps = appArray; } return _apps;}- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.}#pragma mark - 数据源方法- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{ return self.apps.count;}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{ static NSString *ID = @"app"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID]; XMGApp *app = self.apps[indexPath.row]; cell.textLabel.text = app.name; cell.detailTextLabel.text = app.download; // 先从内存缓存中取出图片 UIImage *image = self.imageCache[app.icon]; if (image) { // 内存中有图片 cell.imageView.image = image; } else { // 内存中没有图片 // 获得Library/Caches文件夹 NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; // 获得文件名 NSString *filename = [app.icon lastPathComponent]; // 计算出文件的全路径 NSString *file = [cachesPath stringByAppendingPathComponent:filename]; // 加载沙盒的文件数据 NSData *data = [NSData dataWithContentsOfFile:file]; if (data) { // 直接利用沙盒中图片 cell.imageView.image = [UIImage imageWithData:data]; // 存到字典中 self.imageCache[app.icon] = cell.imageView.image; } else { // 下载图片 data = [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]]; cell.imageView.image = [UIImage imageWithData:data]; // 存到字典中 self.imageCache[app.icon] = cell.imageView.image; // 将图片文件数据写入沙盒中 [data writeToFile:file atomically:YES]; } } return cell;}// [NSDate date];// 获得文件属性// [[NSFileManager defaultManager] attributesOfItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];// 删除文件// [[NSFileManager defaultManager] removeItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];/* Documents Library - Caches - Preference tmp */@end 
// XMGApp.h// 06-掌握-多图片下载#import@interface XMGApp : NSObject/** 图标 */@property (nonatomic, strong) NSString *icon;/** 下载量 */@property (nonatomic, strong) NSString *download;/** 名字 */@property (nonatomic, strong) NSString *name;+ (instancetype)appWithDict:(NSDictionary *)dict;@end
// XMGApp.m// 06-掌握-多图片下载#import "XMGApp.h"@implementation XMGApp+ (instancetype)appWithDict:(NSDictionary *)dict{ XMGApp *app = [[self alloc] init]; [app setValuesForKeysWithDictionary:dict]; return app;}@end
// ViewController.m// 06-掌握-多图片下载#import "ViewController.h"#import "XMGApp.h"@interface ViewController ()/** 所有数据 */@property (nonatomic, strong) NSArray *apps;/** 内存缓存的图片 */@property (nonatomic, strong) NSMutableDictionary *images;/** 队列对象 */@property (nonatomic, strong) NSOperationQueue *queue;@end@implementation ViewController- (NSOperationQueue *)queue{ if (!_queue) { _queue = [[NSOperationQueue alloc] init]; _queue.maxConcurrentOperationCount = 3; } return _queue;}- (NSMutableDictionary *)images{ if (!_images) { _images = [NSMutableDictionary dictionary]; } return _images;}- (NSArray *)apps{ if (!_apps) { NSArray *dictArray = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil]]; NSMutableArray *appArray = [NSMutableArray array]; for (NSDictionary *dict in dictArray) { [appArray addObject:[XMGApp appWithDict:dict]]; } _apps = appArray; } return _apps;}- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.}#pragma mark - 数据源方法- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{ return self.apps.count;}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{ static NSString *ID = @"app"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID]; XMGApp *app = self.apps[indexPath.row]; cell.textLabel.text = app.name; cell.detailTextLabel.text = app.download; // 先从内存缓存中取出图片 UIImage *image = self.images[app.icon]; if (image) { // 内存中有图片 cell.imageView.image = image; } else { // 内存中没有图片 // 获得Library/Caches文件夹 NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; // 获得文件名 NSString *filename = [app.icon lastPathComponent]; // 计算出文件的全路径 NSString *file = [cachesPath stringByAppendingPathComponent:filename]; // 加载沙盒的文件数据 NSData *data = [NSData dataWithContentsOfFile:file]; if (data) { // 直接利用沙盒中图片 UIImage *image = [UIImage imageWithData:data]; cell.imageView.image = image; // 存到字典中 self.images[app.icon] = image; } else { // 下载图片 [self.queue addOperationWithBlock:^{ // 下载图片 NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]]; UIImage *image = [UIImage imageWithData:data]; [NSThread sleepForTimeInterval:1.0]; // 回到主线程显示图片 [[NSOperationQueue mainQueue] addOperationWithBlock:^{ cell.imageView.image = image; }]; // 存到字典中 self.images[app.icon] = image; // 将图片文件数据写入沙盒中 [data writeToFile:file atomically:YES]; }]; } } return cell;}// [NSDate date];// 获得文件属性// [[NSFileManager defaultManager] attributesOfItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];// 删除文件// [[NSFileManager defaultManager] removeItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];/* Documents Library - Caches - Preference tmp */@end 完整版的
//// ViewController.m// 06-掌握-多图片下载//// Created by xiaomage on 15/7/9.// Copyright (c) 2015年 小码哥. All rights reserved.//#import "ViewController.h"#import "XMGApp.h"@interface ViewController ()/** 所有数据 */@property (nonatomic, strong) NSArray *apps;/** 内存缓存的图片 */@property (nonatomic, strong) NSMutableDictionary *images;/** 所有的操作对象 */@property (nonatomic, strong) NSMutableDictionary *operations;/** 队列对象 */@property (nonatomic, strong) NSOperationQueue *queue;@end@implementation ViewController- (NSOperationQueue *)queue{ if (!_queue) { _queue = [[NSOperationQueue alloc] init]; _queue.maxConcurrentOperationCount = 3; } return _queue;}- (NSMutableDictionary *)operations{ if (!_operations) { _operations = [NSMutableDictionary dictionary]; } return _operations;}- (NSMutableDictionary *)images{ if (!_images) { _images = [NSMutableDictionary dictionary]; } return _images;}- (NSArray *)apps{ if (!_apps) { NSArray *dictArray = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"apps.plist" ofType:nil]]; NSMutableArray *appArray = [NSMutableArray array]; for (NSDictionary *dict in dictArray) { [appArray addObject:[XMGApp appWithDict:dict]]; } _apps = appArray; } return _apps;}- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.}- (void)didReceiveMemoryWarning{ [super didReceiveMemoryWarning]; self.images = nil; self.operations = nil; [self.queue cancelAllOperations];}#pragma mark - 数据源方法- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{ return self.apps.count;}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{ static NSString *ID = @"app"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID]; XMGApp *app = self.apps[indexPath.row]; cell.textLabel.text = app.name; cell.detailTextLabel.text = app.download; // 先从内存缓存中取出图片 UIImage *image = self.images[app.icon]; if (image) { // 内存中有图片 cell.imageView.image = image; } else { // 内存中没有图片 // 获得Library/Caches文件夹 NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject]; // 获得文件名 NSString *filename = [app.icon lastPathComponent]; // 计算出文件的全路径 NSString *file = [cachesPath stringByAppendingPathComponent:filename]; // 加载沙盒的文件数据 NSData *data = [NSData dataWithContentsOfFile:file]; if (data) { // 直接利用沙盒中图片 UIImage *image = [UIImage imageWithData:data]; cell.imageView.image = image; // 存到字典中 self.images[app.icon] = image; } else { // 下载图片 cell.imageView.image = [UIImage imageNamed:@"placeholder"]; NSOperation *operation = self.operations[app.icon]; if (operation == nil) { // 这张图片暂时没有下载任务 operation = [NSBlockOperation blockOperationWithBlock:^{ // 下载图片 NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]]; // 数据加载失败 if (data == nil) { // 移除操作 [self.operations removeObjectForKey:app.icon]; return; } UIImage *image = [UIImage imageWithData:data]; // 存到字典中 self.images[app.icon] = image; // 回到主线程显示图片 [[NSOperationQueue mainQueue] addOperationWithBlock:^{ [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone]; }]; // 将图片文件数据写入沙盒中 [data writeToFile:file atomically:YES]; // 移除操作 [self.operations removeObjectForKey:app.icon]; }]; // 添加到队列中 [self.queue addOperation:operation]; // 存放到字典中 self.operations[app.icon] = operation; } } } return cell;}// [NSDate date];// 获得文件属性// [[NSFileManager defaultManager] attributesOfItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];// 删除文件// [[NSFileManager defaultManager] removeItemAtPath:<#(NSString *)#> error:<#(NSError *__autoreleasing *)#>];/* Documents Library - Caches - Preference tmp */@end