SharePoint Property Bag

How to Add new item to property bag

  SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                using (SPSite site = new SPSite("siteUrl"))
                {
                    using (SPWeb web = site.OpenWeb())
                    {
                        web.AllowUnsafeUpdates = true;
                        web.AllProperties.Add("key", "value");
                        web.Update();
                        web.AllowUnsafeUpdates = false;
                    }
                }
            });

How to Read  property from property bag

SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                using (SPSite site = new SPSite("siteUrl"))
                {
                    using (SPWeb web = site.OpenWeb())
                    {
                     
                        if (web.AllProperties.ContainsKey("key"))
                        {
                            MessageBox.Show(web.Properties["key"].ToString());
                        }
                      
                    }
                }
            });