KVO实现自定义文件复制进度展示

　　说明：自定义文件类，通过NSFileManager 以及NSFileHandle 实现文件的创建和copy,为了控制内存的并发使用，通过控制每次赋值的固定长度来分多次复制：

NSString * path=NSHomeDirectory();
    path =[path stringByAppendingPathComponent:@"deskTop/Boby.m"];

    NSString * target=NSHomeDirectory();
    target =[target stringByAppendingPathComponent:@"deskTop/target.m"];

    NSFileManager * manager=[NSFileManager defaultManager];

    //校验并且创建文件
    if(![manager fileExistsAtPath:path]){
        [manager createFileAtPath:path contents:nil attributes:nil];
    }

    if(![manager fileExistsAtPath:target]){
        [manager createFileAtPath:target contents:nil attributes:nil];
    }
    NSDictionary * dic=[manager attributesOfItemAtPath:path error:nil];

    NSFileHandle * handle=[NSFileHandle fileHandleForReadingAtPath:path];
    NSFileHandle * handletTarget=[NSFileHandle fileHandleForWritingAtPath:target];

    int total=(int)[dic[@"NSFileSize"] integerValue];
    self.totalSize=total;
    int per=50;
    int count=total%per==0?total/per:total/per+1;
    for(int i=0;i<count;i++){

        [handle seekToFileOffset:self.nowSize];
        NSData *data= [handle readDataOfLength:per];

        int tem=per*(i+1);
        if(tem>total){
            tem=total;
        }

        self.nowSize=tem;

        [handletTarget seekToEndOfFile];
        [handletTarget writeData:data];
        [NSThread sleepForTimeInterval:0.2];

    }

    [handle closeFile];
[handletTarget closeFile];

　　说明：自定义使用者，通过设置观察者来动态观察当前文件copy的进度并展示到控制台或者输出到UI，并提供方法接口，启动文件拷贝。

- (id) initWithFile:(FileMake *)files{
    self=[super init];

    if(self){
        self.file= files;
        [self.file addObserver:self forKeyPath:@"nowSize" options:NSKeyValueObservingOptionNew context:nil];
    }
    return self;
}

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    CGFloat all=self.file.totalSize;
    CGFloat now=[[change objectForKey:@"new"] floatValue];
    CGFloat result=now/all;
    NSLog(@"%.2f",result);
    //一定不能忘了销毁当前的观察者
    if(result==1){
        [self.file removeObserver:self forKeyPath:@"nowSize"];
    }
}

- (void) begin{
    [self.file startCopy];
}