原理：

制造一个与之空闲磁盘差不多大小的垃圾文件,然后触发苹果的清理机制。清理完后,删除之前生成的垃圾文件。再次统计当前可用存储,差值即为本次清理的垃圾大小。

注意：

系统空闲磁盘耗尽，会卡死。具体如何清除还有待研究……

- (void)viewDidLoad {
  [super viewDidLoad];
  UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(100, 0, 200, 100)];
  [button setTitle:@"清理缓存" forState:UIControlStateNormal];
  button.backgroundColor = [UIColor greenColor];
  [button addTarget:self action:@selector(clearRubbish) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:button];
}

- (void)clearRubbish{
    // 获取Document文件路径
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentpath = [paths objectAtIndex:0];
    // 创建垃圾文件
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *filePath = [documentpath stringByAppendingPathComponent:@"rubbish.txt"];
    if ([fileManager fileExistsAtPath:filePath]) {
        [fileManager removeItemAtPath:filePath error:nil];
    }
    
    [fileManager createFileAtPath:filePath contents:[@"123" dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];
    
    NSDictionary *dict = [fileManager attributesOfItemAtPath:filePath error:nil];
    NSString *fileSize = dict[@"NSFileSize"];
    NSLog(@"制造垃圾文件前:\n");
    NSLog(@"垃圾文件大小:%@ 字节",fileSize);

    // 获取系统磁盘信息
   long long freeSpace = [self getSystemDiskInfo:documentpath];
    
   // 快速制造垃圾文件
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:filePath];
    // 制造的垃圾文件比剩余磁盘空间大
    [handle truncateFileAtOffset:freeSpace + 2];
    dict = [fileManager attributesOfItemAtPath:filePath error:nil];
    fileSize = dict[@"NSFileSize"];
    NSLog(@"制造垃圾文件后:\n");
    NSLog(@"垃圾文件大小:%@ 字节",fileSize);
    
    // 获取系统磁盘信息
    [self getSystemDiskInfo:documentpath];
}

- (long long)getSystemDiskInfo:(NSString *)path{
    NSDictionary *fileSysAttributes = [[NSFileManager defaultManager] attributesOfFileSystemForPath:path error:nil];
    NSNumber *freeSpace = [fileSysAttributes objectForKey:NSFileSystemFreeSize];
    NSNumber *totalSpace = [fileSysAttributes objectForKey:NSFileSystemSize];
    long long freeSize = [freeSpace longLongValue];
    long long totalSize = [totalSpace longLongValue];
    NSLog(@"磁盘已使用 %lld,剩余 %lld\n",(totalSize - freeSize),freeSize);
    return freeSize;
}

5.效果

磁盘空间已满.png