fileExistsAtPath: isDirectory:用法

NSFileManager *fileManager = [NSFileManager defaultManager];
    
    NSString *historyMessage = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    historyMessage = [NSString stringWithFormat:@"%@/historyMessage",historyMessage];
    
    BOOL isDir;
    if (! [fileManager fileExistsAtPath:historyMessage isDirectory:&isDir]) { // isDir判断是否为文件夹
        //[fileManager createFileAtPath:historyMessage contents:nil attributes:nil]; // 在documents下创建一个historyMessage文件，执行后fileExistsAtPath再判断返回YES； 会导致下面创建historyMessage文件夹失败，
        [fileManager createFileAtPath:[NSString stringWithFormat:@"%@.txt",historyMessage] contents:nil attributes:nil]; // 在documents下创建一个historyMessage.txt文件，执行后fileExistsAtPath再判断返回NO； 下面创建historyMessage文件夹成功
        
        [fileManager createDirectoryAtPath:historyMessage withIntermediateDirectories:YES attributes:nil error:nil];
    }