unity5在为ios打包资源的时候，提示：

 error CS0117: `System.IO.File' does not contain a definition for `WriteAllBytes'

很奇怪的问题，后来自己写了读写函数，解决！

    /// 

    /// 擦写文件(用于替换系统File的同名静态方法)
    /// 
    /// 
    /// 
    /// 
    /// 
    public static void WriteAllBytes(string file,byte[] data,int offset = 0,int length = -1)
    {
        if (length == -1) length = data.Length - offset;
        FileStream fs = new FileStream(file, FileMode.Create);
        BinaryWriter w = new BinaryWriter(fs);
        w.Write(data,offset,length);
        w.Flush();
        w.Close();
        fs.Close();
    }

    /// 

    /// 读取文件(用于替换系统File的同名静态方法)
    /// 
    /// 
    /// 
    /// 
    public static byte[] ReadAllBytes(string file)
    {
        FileStream fs = new FileStream(file, FileMode.Open);
        BinaryReader r = new BinaryReader(fs);
        byte[] data = r.ReadBytes((int)fs.Length);
        r.Close();
        fs.Close();
        return data;
    }