小编foo*_*gry的帖子

因为我们知道,我们可以添加使用类别和运行方法,如在Objective-C的变量 objc_setAssociatedObject和objc_getAssociatedObject.例如:

#import <objc/runtime.h>
@interface Person (EmailAddress)
@property (nonatomic, readwrite, copy) NSString *emailAddress;
@end

@implementation Person (EmailAddress)

static char emailAddressKey;

- (NSString *)emailAddress {
    return objc_getAssociatedObject(self, 
                                    &emailAddressKey);
}

- (void)setEmailAddress:(NSString *)emailAddress {
   objc_setAssociatedObject(self, 
                            &emailAddressKey,
                            emailAddress,
                            OBJC_ASSOCIATION_COPY);
}
@end

但有人知道做什么objc_getAssociatedObject或objc_setAssociatedObject做什么？我的意思是,我们添加到对象(这里self)的变量存储在哪里？和变量之间的关系self？

我需要从Internet下载大文件,并将其保存到本地磁盘.

首先,我保存这样的数据:

- (void)saveToLocalFile:(NSData *)data withOffset:(unsigned long long)offset{

    NSString* localFile = [self tempLocalFile];
    dispatch_async(mFileOperationQueue_, ^{

        NSFileHandle* fileHandle = [NSFileHandle fileHandleForWritingAtPath:localFile];
        if (fileHandle == nil) {
            [data writeToFile:localFile atomically:YES];
            return;
        }
        else {
            [fileHandle seekToFileOffset:offset];
            [fileHandle writeData:data];
            [fileHandle closeFile];
        }
    });
}

由于AFNetworking使用NSOutputstream将数据保存到本地是这样的:

NSUInteger length = [data length];
    while (YES) {
        NSInteger totalNumberOfBytesWritten = 0;
        if ([self.outputStream hasSpaceAvailable]) {
            const uint8_t *dataBuffer = (uint8_t *)[data bytes];

            NSInteger numberOfBytesWritten = 0;
            while (totalNumberOfBytesWritten < (NSInteger)length) {
                numberOfBytesWritten = …