HiddenField.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / xsp / System / Web / UI / WebControls / HiddenField.cs / 1 / HiddenField.cs
                        

                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

namespace System.Web.UI.WebControls { 
 
    using System.ComponentModel;
    using System.Security.Permissions; 
    using System.Collections.Specialized;


    ///  
    /// Inserts a hidden field into the web form.
    ///  
    [ 
    ControlValueProperty("Value"),
    DefaultEvent("ValueChanged"), 
    DefaultProperty("Value"),
    Designer("System.Web.UI.Design.WebControls.HiddenFieldDesigner, " + AssemblyRef.SystemDesign),
    ParseChildren(true),
    PersistChildren(false), 
    NonVisualControl(),
    SupportsEventValidation, 
    ] 
    [AspNetHostingPermission(SecurityAction.LinkDemand, Level=AspNetHostingPermissionLevel.Minimal)]
    [AspNetHostingPermission(SecurityAction.InheritanceDemand, Level=AspNetHostingPermissionLevel.Minimal)] 
    public class HiddenField : Control, IPostBackDataHandler {

        private static readonly object EventValueChanged = new object();
 
        [
        DefaultValue(false), 
        EditorBrowsable(EditorBrowsableState.Never), 
        ]
        public override bool EnableTheming { 
            get {
                return false;
            }
            set { 
                throw new NotSupportedException(SR.GetString(SR.NoThemingSupport, this.GetType().Name));
            } 
        } 

        [ 
        DefaultValue(""),
        EditorBrowsable(EditorBrowsableState.Never),
        ]
        public override string SkinID { 
            get {
                return String.Empty; 
            } 
            set {
                throw new NotSupportedException(SR.GetString(SR.NoThemingSupport, this.GetType().Name)); 
            }
        }

 
        /// 
        /// Gets or sets the value of the hidden field. 
        ///  
        [
        Bindable(true), 
        WebCategory("Behavior"),
        DefaultValue(""),
        WebSysDescription(SR.HiddenField_Value)
        ] 
        public virtual string Value {
            get { 
                string s = (string)ViewState["Value"]; 
                return (s != null) ? s : String.Empty;
            } 
            set {
                ViewState["Value"] = value;
            }
        } 

 
        ///  
        /// Raised when the value of the hidden field is changed on the client.
        ///  
        [
        WebCategory("Action"),
        WebSysDescription(SR.HiddenField_OnValueChanged)
        ] 
        public event EventHandler ValueChanged {
            add { 
                Events.AddHandler(EventValueChanged, value); 
            }
            remove { 
                Events.RemoveHandler(EventValueChanged, value);
            }
        }
 

        protected override ControlCollection CreateControlCollection() { 
            return new EmptyControlCollection(this); 
        }
 
        [
        EditorBrowsable(EditorBrowsableState.Never),
        ]
        public override void Focus() { 
            throw new NotSupportedException(SR.GetString(SR.NoFocusSupport, this.GetType().Name));
        } 
 

        protected virtual bool LoadPostData(string postDataKey, NameValueCollection postCollection) { 
            ValidateEvent(UniqueID);

            string current = Value;
            string postData = postCollection[postDataKey]; 
            if (!current.Equals(postData, StringComparison.Ordinal)) {
                Value = postData; 
                return true; 
            }
            return false; 
        }


        protected internal override void OnPreRender(EventArgs e) { 
            base.OnPreRender(e);
            if (SaveValueViewState == false) { 
                ViewState.SetItemDirty("Value", false); 
            }
        } 


        protected virtual void OnValueChanged(EventArgs e) {
            EventHandler handler = (EventHandler)Events[EventValueChanged]; 
            if (handler != null) {
                handler(this, e); 
            } 
        }
 

        protected virtual void RaisePostDataChangedEvent() {
            OnValueChanged(EventArgs.Empty);
        } 

 
        protected internal override void Render(HtmlTextWriter writer) { 
            string uniqueID = UniqueID;
 
            // Make sure we are in a form tag with runat=server.
            if (Page != null) {
                Page.VerifyRenderingInServerForm(this);
                Page.ClientScript.RegisterForEventValidation(uniqueID); 
            }
 
            writer.AddAttribute(HtmlTextWriterAttribute.Type, "hidden"); 

            if (uniqueID != null) { 
                writer.AddAttribute(HtmlTextWriterAttribute.Name, uniqueID);
            }

            if (ID != null) { 
                writer.AddAttribute(HtmlTextWriterAttribute.Id, ClientID);
            } 
 
            string s;
            s = Value; 
            if (s.Length > 0) {
                writer.AddAttribute(HtmlTextWriterAttribute.Value, s);
            }
 
            writer.RenderBeginTag(HtmlTextWriterTag.Input);
            writer.RenderEndTag(); 
        } 

        ///  
        ///    Determines whether the Value must be stored in view state, to
        ///    optimize the size of the saved state.
        /// 
        private bool SaveValueViewState { 
            get {
                // Must be saved when 
                // 1. There is a registered event handler for EventValueChanged 
                // 2. Control is not visible, because the browser's post data will not include this control
                // 3. The instance is a derived instance, which might be overriding the OnValueChanged method 

                if ((Events[EventValueChanged] != null) ||
                    (Visible == false) ||
                    (this.GetType() != typeof(HiddenField))) { 
                    return true;
                } 
 
                return false;
            } 
        }

        #region Implementation of IPostBackDataHandler
 
        bool IPostBackDataHandler.LoadPostData(string postDataKey, NameValueCollection postCollection) {
            return LoadPostData(postDataKey, postCollection); 
        } 

 
        void IPostBackDataHandler.RaisePostDataChangedEvent() {
            RaisePostDataChangedEvent();
        }
        #endregion 
    }
}

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