HiddenField.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / xsp / System / Web / UI / WebControls / HiddenField.cs / 1305376 / HiddenField.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

namespace System.Web.UI.WebControls { 
 
    using System.ComponentModel;
    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,
    ] 
    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
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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HiddenField.cs source code in C# .NET

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