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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