压缩ViewState后，在Convert.FromBase64String时偶尔会发生FormatException

Question

压缩ViewState后，在Convert.FromBase64String时偶尔会发生FormatException，请教是什么原因？以下是BasePage中的相关代码        private bool viewStateCompress = false;        protected bool ViewStateCompress
        {
            set { viewStateCompress = value; }
            get { return viewStateCompress;}
        }        protected override void SavePageStateToPersistenceMedium(object state)
        {
            if (!viewStateCompress)
            { 
                base.SavePageStateToPersistenceMedium(state);
            }
            else
            {
                Pair pair;
                byte[] data;
                byte[] compressedData;
                string compressedStr;
                object viewState = null, controlState = null;                LosFormatter formatter = new LosFormatter();
                commonUtil.CompressHelper CH = commonUtil.CompressHelper.getInstance();
                PageStatePersister persister = this.PageStatePersister;                if (state is Pair)
                {
                    pair = (Pair)state;
                    viewState = pair.First;
                    controlState = pair.Second;
                }
                else
                {
                    base.SavePageStateToPersistenceMedium(state);
                    return;
                }                StringWriter wViewState = new StringWriter();
                StringWriter wControlState = new StringWriter();                formatter.Serialize(wViewState, viewState);
                string viewStateStr = wViewState.ToString();
                data = Convert.FromBase64String(viewStateStr);
                compressedData = CH.Compress(data);
                compressedStr = Convert.ToBase64String(compressedData);
                persister.ViewState = compressedStr;                formatter.Serialize(wControlState, controlState);
                string controlStateStr = wControlState.ToString();
                data = Convert.FromBase64String(controlStateStr);
                compressedData = CH.Compress(data);
                compressedStr = Convert.ToBase64String(compressedData);
                persister.ControlState = compressedStr;                persister.Save();
            }
        }        protected override object LoadPageStateFromPersistenceMedium()
        {
            if (!viewStateCompress)
            { 
                return base.LoadPageStateFromPersistenceMedium();
            }
            else
            {
                byte[] data;
                byte[] uncompressedData;
                string decompressedStr;
                object viewState, controlState;                LosFormatter formatter = new LosFormatter();
                commonUtil.CompressHelper CH = commonUtil.CompressHelper.getInstance();
                PageStatePersister persister = this.PageStatePersister;
                persister.Load();                string viewStateStr = persister.ViewState.ToString();
                string controlStateStr = persister.ControlState.ToString();
                try
                {
                    data = Convert.FromBase64String(viewStateStr);
                    uncompressedData = CH.Decompress(data);
                    decompressedStr = Convert.ToBase64String(uncompressedData);
                    viewState = formatter.Deserialize(decompressedStr);                    data = Convert.FromBase64String(controlStateStr);
                    uncompressedData = CH.Decompress(data);
                    decompressedStr = Convert.ToBase64String(uncompressedData);
                    controlState = formatter.Deserialize(decompressedStr);
                }
                catch(Exception exp)
                { 
                    viewState = null;
                    controlState = null;
                }
                return new Pair(viewState, controlState);
            }
        }

Answer 1

错误发生在LoadPageStateFromPersistenceMedium中的data = Convert.FromBase64String(viewStateStr); 是一个FormatException错误，很奇怪，我放进去的时候肯定是ToBase64了，为什么拿出来的东西会不对呢？

Answer 2

处理过程中没有必要设计base64编码。不论你写出什么二进制值，之后会被重新编码。而读入之前也会自动解码。因此你如果进行bas64编码，应该是额外多做了一道。另外，压缩之前也没有必要base64编码。

Answer 3

我只知道viewstate默认是Base64形式的数据

Answer 4

当Convert.FromBase64String方法的参数s的长度小于 4 或不是 4 的偶数倍时，将会抛出FormatException。
参考
http://www.cnblogs.com/heliguan/articles/1060481.html

Answer 5

不知道你的 commonUtil.CompressHelper 是什么，所以没法测试。我其实怀疑这样能够压缩多少。执行压缩，并且仍然是通过internet上无数的网卡、网线、路由器来回传递，这还是比较复杂的过程。我写了一个简单的过程，不压缩，用磁盘来代替网络，可以参考一下。这里也是输出字符串，但是并不做base64编码解码。
public class XVPage : Page
{
    static private DirectoryInfo _Dir;    private DirectoryInfo Dir
    {
        get
        {
            if (_Dir == null)
            {
                _Dir = new DirectoryInfo(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "App_Data"));
                if (!_Dir.Exists)
                    _Dir.Create();
                _Dir = new DirectoryInfo(Path.Combine(_Dir.FullName, "ViewState"));
                if (!_Dir.Exists)
                    _Dir.Create();
            }
            return _Dir;
        }
    }    protected override object LoadPageStateFromPersistenceMedium()
    {
        PageStatePersister ps = this.PageStatePersister;
        ps.Load();
        if (ps.ControlState != null)
            ps.ControlState = 反序列化对象((string)ps.ControlState);
        if (ps.ViewState != null)
            ps.ViewState = 反序列化对象((string)ps.ViewState);
        return new Pair(ps.ControlState, ps.ViewState);
    }    protected override void SavePageStateToPersistenceMedium(object state)
    {
        PageStatePersister ps = this.PageStatePersister;
        if (state is Pair)
        {
            Pair pair = (Pair)state;
            ps.ControlState = pair.First;
            ps.ViewState = pair.Second;
        }
        else
        {
            ps.ViewState = state;
        }
        if (ps.ControlState != null)
            ps.ControlState = 序列化对象(ps.ControlState);
        if (ps.ViewState != null)
            ps.ViewState = 序列化对象(ps.ViewState);
        ps.Save();
    }    private object 反序列化对象(string stateID)
    {
        string stateStr = (string)Cache[stateID];
        string file = Path.Combine(Dir.FullName, stateID);
        if (stateStr == null)
            stateStr = File.ReadAllText(file);
        else
            Cache.Remove(stateID);
        return new ObjectStateFormatter().Deserialize(stateStr);
    }    private string 序列化对象(object obj)
    {
        string value = new ObjectStateFormatter().Serialize(obj);
        string stateID = (DateTime.Now.Ticks + (long)value.GetHashCode()).ToString(); //产生离散的id号码   
        File.WriteAllText(Path.Combine(Dir.FullName, stateID), value);
        Cache.Insert(stateID, value);
        return stateID;
    }    protected override void OnUnload(EventArgs e)
    {
        base.OnUnload(e);
        DateTime dt = DateTime.Now.AddMinutes(-20);
        foreach (FileInfo fl in Dir.GetFiles())
            if (fl.LastAccessTime < dt)
                try
                {
                    fl.Delete();
                }
                catch
                {
                }
    }
}

Answer 6

你不会是仅仅为了在string与byte[]之间转换就动用了Base64编码解码功能了吧？在调用compressedData = CH.Compress(data);前后，都无需Base64解码和编码，直接把compressedData 从byte[]转换为string就可以了（无需编码）。

Answer 7

多谢sp1234，存放viewstate到文件的做法我也考虑过，可是由于我们服务器上不允许，所以就采用了压缩的办法，对于一些大页面非常有用。我原来的想法是因为viewstate是base64编码的，所以我就ConvertFromBase64->Compress->ConvertToBase64->SaveViewState。先前我采用的是RegisterHiddenField的做法，所以是手工Base64，如果直接存取persist对象可以自动转换base64的话那就太好了。我再debug一下试试看。