1. 获取缓存文件的大小
-( float )readCacheSize
{
    NSString *cachePath = [NSSearchPathForDirectoriesInDomains (NSCachesDirectory , NSUserDomainMask , YES) firstObject];
    return [ self folderSizeAtPath :cachePath];
}


由于缓存文件存在沙箱中，我们可以通过NSFileManager API来实现对缓存文件大小的计算。
// 遍历文件夹获得文件夹大小，返回多少 M
- ( float ) folderSizeAtPath:( NSString *) folderPath{
    
    NSFileManager * manager = [NSFileManager defaultManager];
    if (![manager fileExistsAtPath :folderPath]) return 0 ;
    NSEnumerator *childFilesEnumerator = [[manager subpathsAtPath :folderPath] objectEnumerator];
    NSString * fileName;
    long long folderSize = 0 ;
    while ((fileName = [childFilesEnumerator nextObject]) != nil ){
        //获取文件全路径
        NSString * fileAbsolutePath = [folderPath stringByAppendingPathComponent :fileName];
        folderSize += [ self fileSizeAtPath :fileAbsolutePath];
    }

    return folderSize/( 1024.0 * 1024.0);
    
}



// 计算 单个文件的大小
- ( long long ) fileSizeAtPath:( NSString *) filePath{
    NSFileManager * manager = [NSFileManager defaultManager];
    if ([manager fileExistsAtPath :filePath]){
        return [[manager attributesOfItemAtPath :filePath error : nil] fileSize];
    }
    return 0;
}


- (void)clearFile
{
    NSString * cachePath = [NSSearchPathForDirectoriesInDomains (NSCachesDirectory , NSUserDomainMask , YES ) firstObject];
    NSArray * files = [[NSFileManager defaultManager ] subpathsAtPath :cachePath];
    //NSLog ( @"cachpath = %@" , cachePath);
    for ( NSString * p in files) {
        
        NSError * error = nil ;
        //获取文件全路径
        NSString * fileAbsolutePath = [cachePath stringByAppendingPathComponent :p];
        
        if ([[NSFileManager defaultManager ] fileExistsAtPath :fileAbsolutePath]) {
            [[NSFileManager defaultManager ] removeItemAtPath :fileAbsolutePath error :&error];
        }
    }
    
    //读取缓存大小
    float cacheSize = [self readCacheSize] *1024;
    self.cacheSize.text = [NSString stringWithFormat:@"%.2fKB",cacheSize];

}