Save view state in ASP.NET Cache

CachePageStatePersister.cs

// From: https://weblogs.asp.net/ricardoperes/saving-view-state-in-cache
// Override following property in your pages.
// protected override PageStatePersister PageStatePersister
// {
//     get
//     {
//         return (new CachePageStatePersister(this));
//     }
// }
public class CachePageStatePersister : PageStatePersister
{
    private const String RequestId = "__REQUESTID";
    private const String ViewStateId = "VIEWSTATE:{0}";
    private const String ControlStateId = "CONTROLSTATE:{0}";
    private const String CacheTimeoutMinutesKey = "CacheTimeoutMinutes";
 
    private const Int32 DefaultCacheTimeoutMinutes = 10;
 
    public CachePageStatePersister(Page page): base(page)
    {
 
    }
 
    public override void Load()
    {
        String id = this.Page.ID;
 
        if ((String.IsNullOrWhiteSpace(id) == true) || (id == "__Page"))
        {
            id = this.Page.Request.Form[RequestId];
        }
 
        if (String.IsNullOrWhiteSpace(id) == true)
        {
            throw (new InvalidOperationException("Missing page id"));
        }
 
        this.Page.ID = id;
 
        this.Page.ClientScript.RegisterHiddenField(RequestId, id);
 
        String viewStateId = String.Format(ViewStateId, id);
        String controlStateId = String.Format(ControlStateId, id);
 
        this.ViewState = this.Page.Cache[viewStateId];
        this.ControlState = this.Page.Cache[controlStateId];
    }
 
    public override void Save()
    {
        if ((this.ControlState != null) || (this.ViewState != null))
        {
            String id = this.Page.ID;
 
            if ((String.IsNullOrWhiteSpace(id) == true) || (id == "__Page"))
            {
                id = Guid.NewGuid().ToString();
 
                this.Page.ID = id;
 
                this.Page.ClientScript.RegisterHiddenField(RequestId, id);
            }
 
            Int32 cacheTimeoutMinutes = DefaultCacheTimeoutMinutes;
 
            if (String.IsNullOrWhiteSpace(ConfigurationManager.AppSettings[CacheTimeoutMinutesKey]) == false)
            {
                Int32.TryParse(ConfigurationManager.AppSettings[CacheTimeoutMinutesKey], out cacheTimeoutMinutes);
            }
 
            if (this.Page.Items[CacheTimeoutMinutesKey] is Int32)
            {
                cacheTimeoutMinutes = (Int32)this.Page.Items[CacheTimeoutMinutesKey];
            }
 
            String viewStateId = String.Format(ViewStateId, id);
            String controlStateId = String.Format(ControlStateId, id);
 
            if (this.ViewState != null)
            {
                this.Page.Cache.Add(viewStateId, this.ViewState, null, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(cacheTimeoutMinutes), System.Web.Caching.CacheItemPriority.Default, null);
            }
 
            if (this.ControlState != null)
            {
                this.Page.Cache.Add(controlStateId, this.ControlState, null, System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(cacheTimeoutMinutes), System.Web.Caching.CacheItemPriority.Default, null);
            }
        }
    }
}