AFNetworking源码探究（一） —— 基本介绍

#import <Foundation/Foundation.h>

#import <TargetConditionals.h>

#if TARGET_OS_IOS || TARGET_OS_TV

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@class AFImageDownloader;

/**
 This category adds methods to the UIKit framework's `UIButton` class. The methods in this category provide support for loading remote images and background images asynchronously from a URL.

 @warning Compound values for control `state` (such as `UIControlStateHighlighted | UIControlStateDisabled`) are unsupported.
 */
@interface UIButton (AFNetworking)

///------------------------------------
/// @name Accessing the Image Downloader
///------------------------------------

/**
 Set the shared image downloader used to download images.

 @param imageDownloader The shared image downloader used to download images.
*/
+ (void)setSharedImageDownloader:(AFImageDownloader *)imageDownloader;

/**
 The shared image downloader used to download images.
 */
+ (AFImageDownloader *)sharedImageDownloader;

///--------------------
/// @name Setting Image
///--------------------

/**
 Asynchronously downloads an image from the specified URL, and sets it as the image for the specified state once the request is finished. Any previous image request for the receiver will be cancelled.

  If the image is cached locally, the image is set immediately, otherwise the specified placeholder image will be set immediately, and then the remote image will be set once the request is finished.

 @param state The control state.
 @param url The URL used for the image request.
 */
- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url;

/**
 Asynchronously downloads an image from the specified URL, and sets it as the image for the specified state once the request is finished. Any previous image request for the receiver will be cancelled.

 If the image is cached locally, the image is set immediately, otherwise the specified placeholder image will be set immediately, and then the remote image will be set once the request is finished.

 @param state The control state.
 @param url The URL used for the image request.
 @param placeholderImage The image to be set initially, until the image request finishes. If `nil`, the button will not change its image until the image request finishes.
 */
- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url
        placeholderImage:(nullable UIImage *)placeholderImage;

/**
 Asynchronously downloads an image from the specified URL request, and sets it as the image for the specified state once the request is finished. Any previous image request for the receiver will be cancelled.

 If the image is cached locally, the image is set immediately, otherwise the specified placeholder image will be set immediately, and then the remote image will be set once the request is finished.

 If a success block is specified, it is the responsibility of the block to set the image of the button before returning. If no success block is specified, the default behavior of setting the image with `setImage:forState:` is applied.

 @param state The control state.
 @param urlRequest The URL request used for the image request.
 @param placeholderImage The image to be set initially, until the image request finishes. If `nil`, the button will not change its image until the image request finishes.
 @param success A block to be executed when the image data task finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the image created from the response data of request. If the image was returned from cache, the response parameter will be `nil`.
 @param failure A block object to be executed when the image data task finishes unsuccessfully, or that finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the error object describing the network or parsing error that occurred.
 */
- (void)setImageForState:(UIControlState)state
          withURLRequest:(NSURLRequest *)urlRequest
        placeholderImage:(nullable UIImage *)placeholderImage
                 success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                 failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure;


///-------------------------------
/// @name Setting Background Image
///-------------------------------

/**
 Asynchronously downloads an image from the specified URL, and sets it as the background image for the specified state once the request is finished. Any previous background image request for the receiver will be cancelled.

 If the background image is cached locally, the background image is set immediately, otherwise the specified placeholder background image will be set immediately, and then the remote background image will be set once the request is finished.

 @param state The control state.
 @param url The URL used for the background image request.
 */
- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url;

/**
 Asynchronously downloads an image from the specified URL, and sets it as the background image for the specified state once the request is finished. Any previous image request for the receiver will be cancelled.

 If the image is cached locally, the image is set immediately, otherwise the specified placeholder image will be set immediately, and then the remote image will be set once the request is finished.

 @param state The control state.
 @param url The URL used for the background image request.
 @param placeholderImage The background image to be set initially, until the background image request finishes. If `nil`, the button will not change its background image until the background image request finishes.
 */
- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url
                  placeholderImage:(nullable UIImage *)placeholderImage;

/**
 Asynchronously downloads an image from the specified URL request, and sets it as the image for the specified state once the request is finished. Any previous image request for the receiver will be cancelled.

 If the image is cached locally, the image is set immediately, otherwise the specified placeholder image will be set immediately, and then the remote image will be set once the request is finished.

 If a success block is specified, it is the responsibility of the block to set the image of the button before returning. If no success block is specified, the default behavior of setting the image with `setBackgroundImage:forState:` is applied.

 @param state The control state.
 @param urlRequest The URL request used for the image request.
 @param placeholderImage The background image to be set initially, until the background image request finishes. If `nil`, the button will not change its background image until the background image request finishes.
 @param success A block to be executed when the image data task finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the image created from the response data of request. If the image was returned from cache, the response parameter will be `nil`.
 @param failure A block object to be executed when the image data task finishes unsuccessfully, or that finishes successfully. This block has no return value and takes three arguments: the request sent from the client, the response received from the server, and the error object describing the network or parsing error that occurred.
 */
- (void)setBackgroundImageForState:(UIControlState)state
                    withURLRequest:(NSURLRequest *)urlRequest
                  placeholderImage:(nullable UIImage *)placeholderImage
                           success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                           failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure;


///------------------------------
/// @name Canceling Image Loading
///------------------------------

/**
 Cancels any executing image task for the specified control state of the receiver, if one exists.

 @param state The control state.
 */
- (void)cancelImageDownloadTaskForState:(UIControlState)state;

/**
 Cancels any executing background image task for the specified control state of the receiver, if one exists.

 @param state The control state.
 */
- (void)cancelBackgroundImageDownloadTaskForState:(UIControlState)state;

@end

NS_ASSUME_NONNULL_END

#endif

/**
 Set the shared image downloader used to download images.

 @param imageDownloader The shared image downloader used to download images.
*/
+ (void)setSharedImageDownloader:(AFImageDownloader *)imageDownloader;

/**
 The shared image downloader used to download images.
 */
+ (AFImageDownloader *)sharedImageDownloader;

+ (AFImageDownloader *)sharedImageDownloader {

    return objc_getAssociatedObject(self, @selector(sharedImageDownloader)) ?: [AFImageDownloader defaultInstance];
}

+ (void)setSharedImageDownloader:(AFImageDownloader *)imageDownloader {
    objc_setAssociatedObject(self, @selector(sharedImageDownloader), imageDownloader, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url;
- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url
        placeholderImage:(nullable UIImage *)placeholderImage;
- (void)setImageForState:(UIControlState)state
          withURLRequest:(NSURLRequest *)urlRequest
        placeholderImage:(nullable UIImage *)placeholderImage
                 success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                 failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure;

- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url
{
    [self setImageForState:state withURL:url placeholderImage:nil];
}

- (void)setImageForState:(UIControlState)state
                 withURL:(NSURL *)url
        placeholderImage:(UIImage *)placeholderImage
{
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];

    [self setImageForState:state withURLRequest:request placeholderImage:placeholderImage success:nil failure:nil];
}

- (void)setImageForState:(UIControlState)state
          withURLRequest:(NSURLRequest *)urlRequest
        placeholderImage:(nullable UIImage *)placeholderImage
                 success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                 failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure
{
    if ([self isActiveTaskURLEqualToURLRequest:urlRequest forState:state]) {
        return;
    }

    [self cancelImageDownloadTaskForState:state];

    AFImageDownloader *downloader = [[self class] sharedImageDownloader];
    id <AFImageRequestCache> imageCache = downloader.imageCache;

    //Use the image from the image cache if it exists
    UIImage *cachedImage = [imageCache imageforRequest:urlRequest withAdditionalIdentifier:nil];
    if (cachedImage) {
        if (success) {
            success(urlRequest, nil, cachedImage);
        } else {
            [self setImage:cachedImage forState:state];
        }
        [self af_setImageDownloadReceipt:nil forState:state];
    } else {
        if (placeholderImage) {
            [self setImage:placeholderImage forState:state];
        }

        __weak __typeof(self)weakSelf = self;
        NSUUID *downloadID = [NSUUID UUID];
        AFImageDownloadReceipt *receipt;
        receipt = [downloader
                   downloadImageForURLRequest:urlRequest
                   withReceiptID:downloadID
                   success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull responseObject) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                       if ([[strongSelf af_imageDownloadReceiptForState:state].receiptID isEqual:downloadID]) {
                           if (success) {
                               success(request, response, responseObject);
                           } else if(responseObject) {
                               [strongSelf setImage:responseObject forState:state];
                           }
                           [strongSelf af_setImageDownloadReceipt:nil forState:state];
                       }

                   }
                   failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                       if ([[strongSelf af_imageDownloadReceiptForState:state].receiptID isEqual:downloadID]) {
                           if (failure) {
                               failure(request, response, error);
                           }
                           [strongSelf  af_setImageDownloadReceipt:nil forState:state];
                       }
                   }];

        [self af_setImageDownloadReceipt:receipt forState:state];
    }
}

- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url;
- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url
                  placeholderImage:(nullable UIImage *)placeholderImage;
- (void)setBackgroundImageForState:(UIControlState)state
                    withURLRequest:(NSURLRequest *)urlRequest
                  placeholderImage:(nullable UIImage *)placeholderImage
                           success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                           failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure;

- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url
{
    [self setBackgroundImageForState:state withURL:url placeholderImage:nil];
}

- (void)setBackgroundImageForState:(UIControlState)state
                           withURL:(NSURL *)url
                  placeholderImage:(nullable UIImage *)placeholderImage
{
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];

    [self setBackgroundImageForState:state withURLRequest:request placeholderImage:placeholderImage success:nil failure:nil];
}

- (void)setBackgroundImageForState:(UIControlState)state
                    withURLRequest:(NSURLRequest *)urlRequest
                  placeholderImage:(nullable UIImage *)placeholderImage
                           success:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, UIImage *image))success
                           failure:(nullable void (^)(NSURLRequest *request, NSHTTPURLResponse * _Nullable response, NSError *error))failure
{
    if ([self isActiveBackgroundTaskURLEqualToURLRequest:urlRequest forState:state]) {
        return;
    }

    [self cancelBackgroundImageDownloadTaskForState:state];

    AFImageDownloader *downloader = [[self class] sharedImageDownloader];
    id <AFImageRequestCache> imageCache = downloader.imageCache;

    //Use the image from the image cache if it exists
    UIImage *cachedImage = [imageCache imageforRequest:urlRequest withAdditionalIdentifier:nil];
    if (cachedImage) {
        if (success) {
            success(urlRequest, nil, cachedImage);
        } else {
            [self setBackgroundImage:cachedImage forState:state];
        }
        [self af_setBackgroundImageDownloadReceipt:nil forState:state];
    } else {
        if (placeholderImage) {
            [self setBackgroundImage:placeholderImage forState:state];
        }

        __weak __typeof(self)weakSelf = self;
        NSUUID *downloadID = [NSUUID UUID];
        AFImageDownloadReceipt *receipt;
        receipt = [downloader
                   downloadImageForURLRequest:urlRequest
                   withReceiptID:downloadID
                   success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull responseObject) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                       if ([[strongSelf af_backgroundImageDownloadReceiptForState:state].receiptID isEqual:downloadID]) {
                           if (success) {
                               success(request, response, responseObject);
                           } else if(responseObject) {
                               [strongSelf setBackgroundImage:responseObject forState:state];
                           }
                           [strongSelf af_setBackgroundImageDownloadReceipt:nil forState:state];
                       }

                   }
                   failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
                       __strong __typeof(weakSelf)strongSelf = weakSelf;
                       if ([[strongSelf af_backgroundImageDownloadReceiptForState:state].receiptID isEqual:downloadID]) {
                           if (failure) {
                               failure(request, response, error);
                           }
                           [strongSelf  af_setBackgroundImageDownloadReceipt:nil forState:state];
                       }
                   }];

        [self af_setBackgroundImageDownloadReceipt:receipt forState:state];
    }
}