我可以从网站下载图片并将其永久保存在我的应用程序中吗？我真的不知道，但它会为我的应用程序提供一个很好的功能。
答案 0 :(得分：51)
使用缓存的异步下载图像
Asynchronous downloaded images with caching
Here is one more repos which can be used to download images in background
答案 1 :(得分：38)
您无法在应用套装中保存任何内容，但可以使用+[NSData dataWithContentsOfURL:]将图像存储在应用的文档目录中，例如：
NSData *imageData = [NSData dataWithContentsOfURL:myImageURL];
NSString *imagePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"/myImage.png"];
[imageData writeToFile:imagePath atomically:YES];
不完全永久，但它至少会在用户删除应用之前保持不变。
答案 2 :(得分：13)
这是主要概念。玩得开心;）
NSURL *url = [NSURL URLWithString:@"http://example.com/yourImage.png"];
NSData *data = [NSData dataWithContentsOfURL:url];
NSString *path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
path = [path stringByAppendingString:@"/yourLocalImage.png"];
[data writeToFile:path atomically:YES];
答案 3 :(得分：7)
由于我们现在在IO5上，您不再需要将图像写入磁盘 您现在可以在coredata二进制属性上设置“允许外部存储”。 根据苹果发行说明，它意味着以下内容：
图像缩略图等小数据值可以有效地存储在 数据库，但大型照片或其他媒体最好直接处理 文件系统。您现在可以指定托管的值 对象属性可以存储为外部记录 - 请参阅setAllowsExternalBinaryDataStorage: 启用后，核心数据启发式决定是否按值计算 它应该直接在数据库中保存数据或将URI存储到 它为您管理的单独文件。你无法根据查询 如果使用此选项，则为二进制数据属性的内容。
答案 4 :(得分：3)
正如其他人所说，在很多情况下你应该在后台线程中下载图片而不会阻塞用户界面
在这种情况下，我最喜欢的解决方案是使用方便的方法，例如：（credit - ＆gt; iOS: How To Download Images Asynchronously (And Make Your UITableView Scroll Fast)）
- (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, UIImage *image))completionBlock
{
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if ( !error )
{
UIImage *image = [[UIImage alloc] initWithData:data];
completionBlock(YES,image);
} else{
completionBlock(NO,nil);
}
}];
}
并称之为
NSURL *imageUrl = //...
[[MyUtilManager sharedInstance] downloadImageWithURL:[NSURL URLWithString:imageURL] completionBlock:^(BOOL succeeded, UIImage *image) {
//Here you can save the image permanently, update UI and do what you want...
}];
答案 5 :(得分：1)
以下是我下载广告横幅的方式。如果您正在下载大图像或一堆图像，最好在后台进行。
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelectorInBackground:@selector(loadImageIntoMemory) withObject:nil];
}
- (void)loadImageIntoMemory {
NSString *temp_Image_String = [[NSString alloc] initWithFormat:@"http://yourwebsite.com/MyImageName.jpg"];
NSURL *url_For_Ad_Image = [[NSURL alloc] initWithString:temp_Image_String];
NSData *data_For_Ad_Image = [[NSData alloc] initWithContentsOfURL:url_For_Ad_Image];
UIImage *temp_Ad_Image = [[UIImage alloc] initWithData:data_For_Ad_Image];
[self saveImage:temp_Ad_Image];
UIImageView *imageViewForAdImages = [[UIImageView alloc] init];
imageViewForAdImages.frame = CGRectMake(0, 0, 320, 50);
imageViewForAdImages.image = [self loadImage];
[self.view addSubview:imageViewForAdImages];
}
- (void)saveImage: (UIImage*)image {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString* path = [documentsDirectory stringByAppendingPathComponent: @"MyImageName.jpg" ];
NSData* data = UIImagePNGRepresentation(image);
[data writeToFile:path atomically:YES];
}
- (UIImage*)loadImage {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString* path = [documentsDirectory stringByAppendingPathComponent:@"MyImageName.jpg" ];
UIImage* image = [UIImage imageWithContentsOfFile:path];
return image;
}
答案 6 :(得分：1)
以下是从网址异步下载图片的代码，然后在objective-c中保存到您想要的位置： - ＆gt;
+ (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, UIImage *image))completionBlock
{
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if ( !error )
{
UIImage *image = [[UIImage alloc] initWithData:data];
completionBlock(YES,image);
} else{
completionBlock(NO,nil);
}
}];
}
答案 7 :(得分：0)
如果您使用AFNetworking库下载图像并且图像正在UITableview中使用，那么您可以在cellForRowAtIndexPath中使用以下代码
[self setImageWithURL:user.user_ProfilePicturePath toControl:cell.imgView];
-(void)setImageWithURL:(NSURL*)url toControl:(id)ctrl
{
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
if (image) {
if([ctrl isKindOfClass:[UIButton class]])
{
UIButton btn =(UIButton)ctrl;
[btn setBackgroundImage:image forState:UIControlStateNormal];
}
else
{
UIImageView imgView = (UIImageView)ctrl;
imgView.image = image;
}
}
}
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
NSLog(@"No Image");
}];
[operation start];}
答案 8 :(得分：0)
您可以使用NSURLSessionDataTask在不阻止UI的情况下下载图像。
+(void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, UIImage *image))completionBlock
{
NSURLSessionDataTask* _sessionTask = [[NSURLSession sharedSession] dataTaskWithRequest:[NSURLRequest requestWithURL:url]
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (error != nil)
{
if ([error code] == NSURLErrorAppTransportSecurityRequiresSecureConnection)
{
completionBlock(NO,nil);
}
}
else
{
[[NSOperationQueue mainQueue] addOperationWithBlock: ^{
dispatch_async(dispatch_get_main_queue(), ^{
UIImage *image = [[UIImage alloc] initWithData:data];
completionBlock(YES,image);
});
}];
}
}];
[_sessionTask resume];
}
答案 9 :(得分：0)
这是 Swift 5 解决方案，用于通过使用Alamofire下载图像或将文件或一般文件保存到文档目录：
func dowloadAndSaveFile(from url: URL) {
let destination: DownloadRequest.DownloadFileDestination = { _, _ in
var documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
documentsURL.appendPathComponent(url.lastPathComponent)
return (documentsURL, [.removePreviousFile])
}
let request = SessionManager.default.download(url, method: .get, to: destination)
request.validate().responseData { response in
switch response.result {
case .success:
if let destinationURL = response.destinationURL {
print(destinationURL)
}
case .failure(let error):
print(error.localizedDescription)
}
}
}