我正在开发一个应用程序，我需要永久下载和存储图像，直到我手动删除它们（内存中+磁盘）。这是必需的，因为应用程序需要能够脱机工作。我知道AFNetworking和SDWebImage用于缓存图像，但我认为它们不允许永久缓存和手动删除。 Afaik，他们在缓存过期时自动删除图像。
还有其他的库来做这种事吗？我试图为此写一个类，但它不能很稳定。我想最好不要重新发明轮子。
答案 0 :(得分：0)
将文件保存在Application Support中的文件夹中。这些将持续存在，iOS不会删除它们。我说以后再使用一个文件夹，如果你想删除它们，你可以删除该文件夹。
具体如何访问和配置应用程序支持目录详细in this post
如果需要，可以在Core Data存储库中保存这些图像的URL或路径。
编辑：我有一个管理我的Core Data图像存储库的单例类。具有与之关联的图像的对象具有data属性，URL属性，filePath属性和布尔标志，该标志指示是否存在未完成的提取。当某些东西需要图像时，它会询问图像（由数据构造），如果没有数据，则单例会为其发出网络提取。当它到达时，它将存储在文件系统中，并且实体获取该图像集的filePath。然后它发出通知，告知此类图像已到达。 [为了调试，我在各个点测试过以确保我可以从数据中创建图像。]
当viewControllers获取通知时，它们会查看可见单元格列表，如果其中任何一个与新到达的图像相关联，则该类会从单例中请求图像，然后将其设置在单元格上。这对我很有用。
答案 1 :(得分：0)
不幸的是SDWebImage不提供这样的功能 所以为了利用SDWebImage提供的高级缓存功能，我编写了一个围绕SDWebImage的包装器
基本上这个类管理一个后备永久缓存，所以如果在SDWeb图像缓存中没有找到所请求的图像＆＃34;磁盘和内存＆＃34;它将在永久缓存中寻找它
使用这种方法，我设法通过SDWebImage保持像往常一样平滑的图像单元格
.h文件
@interface CacheManager : NSObject
+ (CacheManager*)sharedManager;
// Images
- (BOOL) diskImageExistsForURL:(NSURL*) url;
- (void) downloadImage:(NSURL*) url completed:(void(^)(UIImage*))onComplete;
- (void) setImage:(NSURL*)url toImageView:(UIImageView*)iv completed:(void(^)(UIImage*))onComplete;
- (void) clearImageCache;
@end
.m文件
#import "CacheManager.h"
#import <SDWebImage/UIImageView+WebCache.h>
#define CACH_IMAGES_FOLDER @"ImagesData"
@implementation CacheManager
static CacheManager *sharedManager = nil;
#pragma mark -
#pragma mark Singilton Init Methods
// init shared Cache singleton.
+ (CacheManager*)sharedManager{
@synchronized(self){
if ( !sharedManager ){
sharedManager = [[CacheManager alloc] init];
}
}
return sharedManager;
}
// Dealloc shared API singleton.
+ (id)alloc{
@synchronized( self ){
NSAssert(sharedManager == nil, @"Attempted to allocate a second instance of a singleton.");
return [super alloc];
}
return nil;
}
// Init the manager
- (id)init{
if ( self = [super init] ){}
return self;
}
/**
@returns YES if image found in the permanent cache or the cache managed by SDWebImage lib
*/
- (BOOL) diskImageExistsForURL:(NSURL*) url{
// look for image in the SDWebImage cache
SDWebImageManager *manager = [SDWebImageManager sharedManager];
if([manager diskImageExistsForURL:url])
return YES;
// look for image in the permanent cache
NSString *stringPath = url.path;
NSFileManager *fileManager = [NSFileManager defaultManager];
return [fileManager fileExistsAtPath:stringPath];
}
/**
get the image with specified remote url asynchronosly
first looks for the image in SDWeb cache to make use of the disk and memory cache provided by SDWebImage
if not found, looks for it in the permanent cache we are managing, finally if not found in either places
it will download it using SDWebImage and cache it.
*/
- (void) downloadImage:(NSURL*) url completed:(void(^)(UIImage*))onComplete{
NSString *localPath = [[self getLocalUrlForImageUrl:url] path];
NSFileManager *fileManager = [NSFileManager defaultManager];
// -1 look for image in SDWeb cache
SDWebImageManager *manager = [SDWebImageManager sharedManager];
if([manager diskImageExistsForURL:url]){
[manager downloadImageWithURL:url options:SDWebImageRetryFailed
progress:^(NSInteger receivedSize, NSInteger expectedSize) {}
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
onComplete(image);
// save the image to the perminant cache for later
// if not saved before
if(image){
if ([fileManager fileExistsAtPath:localPath]){
NSURL* localeUrl = [self getLocalUrlForImageUrl:url];
[self saveImage:image toCacheWithLocalPath:localeUrl];
}
}
}];
return;
}
// -2 look for the image in the permanent cache
if ([fileManager fileExistsAtPath:localPath]){
UIImage *img = [self getImageFromCache:url];
onComplete(img);
// save image back to the SDWeb image cache to make use of the memory cache
// provided by SDWebImage in later requests
[manager saveImageToCache:img forURL:url];
return;
}
// -3 download the image using SDWebImage lib
[manager downloadImageWithURL:url options:SDWebImageRetryFailed
progress:^(NSInteger receivedSize, NSInteger expectedSize) {}
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
onComplete(image);
// save the image to the permanent cache for later
if(image){
NSURL* localeUrl = [self getLocalUrlForImageUrl:url];
[self saveImage:image toCacheWithLocalPath:localeUrl];
}
}];
}
- (void) setImage:(NSURL*)url toImageView:(UIImageView*)iv completed:(void(^)(UIImage*))onComplete{
[self downloadImage:url completed:^(UIImage * downloadedImage) {
iv.image = downloadedImage;
onComplete(downloadedImage);
}];
}
/**
@param:imgUrl : local url of image to read
*/
- (UIImage*) getImageFromCache:(NSURL*)imgUrl{
return [UIImage imageWithData: [NSData dataWithContentsOfURL:imgUrl]];
}
/**
writes the suplied image to the local path provided
*/
-(void) saveImage:(UIImage*)img toCacheWithLocalPath:(NSURL*)localPath{
NSData * binaryImageData = UIImagePNGRepresentation(img);
[binaryImageData writeToFile:[localPath path] atomically:YES];
}
// Generate local image URL baesd on the name of the remote image
// this assumes the remote images already has unique names
- (NSURL*)getLocalUrlForImageUrl:(NSURL*)imgUrl{
// Saving an offline copy of the data.
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *cachesDirectory = [paths objectAtIndex:0];
NSString *folderPath = [cachesDirectory stringByAppendingPathComponent:CACH_IMAGES_FOLDER];
BOOL isDir;
// create folder not exist
if (![fileManager fileExistsAtPath:folderPath isDirectory:&isDir]){
NSError *dirWriteError = nil;
if (![fileManager createDirectoryAtPath:folderPath withIntermediateDirectories:YES attributes:nil error:&dirWriteError]){
NSLog(@"Error: failed to create folder!");
}
}
NSString *imgName = [[[imgUrl path] lastPathComponent] stringByDeletingPathExtension];
NSURL *cachesDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSCachesDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
NSString *pathString = [NSString stringWithFormat:@"%@/%@", CACH_IMAGES_FOLDER, imgName];
return [cachesDirectoryURL URLByAppendingPathComponent:pathString];
}
/**
removes the folder contating the cahced images,
the folder will be reacreated whenever a new image is being saved to the permanent cache
*/
-(void)clearImageCache{
// set the directory path
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *cachesDirectory = [paths objectAtIndex:0];
NSString *folderPath = [cachesDirectory stringByAppendingPathComponent:CACH_IMAGES_FOLDER];
BOOL isDir;
NSError *dirError = nil;
// folder exist
if ([fileManager fileExistsAtPath:folderPath isDirectory:&isDir]){
if (![fileManager removeItemAtPath:folderPath error:&dirError])
NSLog(@"Failed to remove folder");
}
}
@end