自己写的一个按钮控件 点击时在界面出现一个loading遮罩层

               

Imports System.Collections.GenericImports System.ComponentModelImports System.TextImports System.WebImports System.Web.UIImports System.Web.UI.WebControlsNamespace Web.Controls    ''' <summary>    ''' Represents a button to prevent duplicate submissions.     ''' When the user clicks the button after the button is grayed out, can not click again until reload the page or jump.    ''' </summary>    <DefaultProperty("Text")> _        <ToolboxData("<{0}:ClickOnceButton runat=server></{0}:ClickOnceButton>")> _Public Class ClickOnceButton        Inherits System.Web.UI.WebControls.Button        ''' <summary>        ''' The default constructor.        ''' </summary>        Public Sub New()            Me.ViewState("afterSubmitText") = "Submitting, please wait ..."            MyBase.Text = "ClickOnceButton"            Me.ViewState("showMessageBox") = False            Me.ViewState("showLoadingLayer") = False            Me.ViewState("warningText") = "Sure to submit it?"        End Sub        ''' <summary>        ''' Gets or sets the click of a button, the button on the display text.        ''' </summary>        <Bindable(True), Category("Appearance"), DefaultValue("Submitting, please wait ..."), Description("After the submission instructions click the button on the display text.")> _        Public Property AfterSubmitText() As String            Get                Dim afterSubmitText__1 As String = DirectCast(Me.ViewState("afterSubmitText"), String)                If afterSubmitText__1 IsNot Nothing Then                    Return afterSubmitText__1                Else                    Return String.Empty                End If            End Get            Set(ByVal value As String)                Me.ViewState("afterSubmitText") = value            End Set        End Property        <Bindable(True), Category("Appearance"), DefaultValue(False), Description("Indicates whether to display a prompt box.")> _        Public Property ShowLoadingLayer() As Boolean            Get                Return CBool(Me.ViewState("showLoadingLayer"))            End Get            Set(ByVal value As Boolean)                Me.ViewState("showLoadingLayer") = value            End Set        End Property        <Bindable(True), Category("Appearance"), DefaultValue(False), Description("Indicates whether to display a prompt box.")> _        Public Property ShowMessageBox() As Boolean            Get                Return CBool(Me.ViewState("showMessageBox"))            End Get            Set(ByVal value As Boolean)                Me.ViewState("showMessageBox") = value            End Set        End Property        <Bindable(True), Category("Appearance"), DefaultValue("Sure to submit it?"), Description("Instructions contained in the contents of the prompt box.")> _        Public Property WarningText() As String            Get                Return DirectCast(Me.ViewState("warningText"), String)            End Get            Set(ByVal value As String)                Me.ViewState("warningText") = value            End Set        End Property        ''' <summary>        ''' AddAttributesToRender        ''' </summary>        ''' <param name="writer">HtmlTextWriter</param>        Protected Overrides Sub AddAttributesToRender(ByVal writer As HtmlTextWriter)            Dim ClientSideEventReference As New System.Text.StringBuilder()            If ((Me.Page IsNot Nothing) AndAlso Me.CausesValidation) AndAlso (Me.Page.Validators.Count > 0) Then                ClientSideEventReference.Append("if (typeof(Page_ClientValidate) == 'function'){if (Page_ClientValidate() == false){return false;}}")            End If            'ShowMessageBox?            If Me.ShowMessageBox Then                ClientSideEventReference.Append("if (!confirm('" & Me.WarningText & "')){return false}")            End If            If Me.ShowLoadingLayer Then                ClientSideEventReference.Append("var objImg = document.createElement(""IMG"");")                ClientSideEventReference.Append("objImg.src= ""Images/LoadingContent.gif"";")                ClientSideEventReference.Append("var iMsk = document.createElement(""div"");")                ClientSideEventReference.Append("document.body.appendChild(iMsk);")                ClientSideEventReference.Append("iMsk.id = ""mask"";")                ClientSideEventReference.Append("iMsk.style.position = ""absolute"";")                ClientSideEventReference.Append("iMsk.style.zIndex = ""1"";")                ClientSideEventReference.Append("iMsk.style.width = ""100%"";")                ClientSideEventReference.Append("iMsk.style.height = ""100%"";")                ClientSideEventReference.Append("iMsk.style.align = ""center"";")                ClientSideEventReference.Append("iMsk.style.top = ""0px"";")                ClientSideEventReference.Append("iMsk.style.left = ""0px"";")                ClientSideEventReference.Append("iMsk.style.background = ""#000"";")                ClientSideEventReference.Append("iMsk.style.filter = ""alpha(opacity=30)"";")                ClientSideEventReference.Append("iMsk.style.opacity = ""0.30"";")                ClientSideEventReference.Append("iMsk.appendChild(objImg);")                ClientSideEventReference.Append("var height = document.body.scrollHeight;")                ClientSideEventReference.Append("var width = document.body.scrollWidth;")                ClientSideEventReference.Append("if(objImg.readystate=""complete""){")                ClientSideEventReference.Append("objImg.style.marginTop = (height - objImg.offsetHeight) / 2 + ""px"";")                ClientSideEventReference.Append("objImg.style.marginLeft = (width - objImg.offsetWidth) / 2 + ""px"";")                ClientSideEventReference.Append("}")                ClientSideEventReference.Append("objImg.style.position = ""absolute"";")            End If            ClientSideEventReference.AppendFormat("this.value = '{0}';", DirectCast(Me.ViewState("afterSubmitText"), String))            ClientSideEventReference.Append("this.disabled = true;")            ClientSideEventReference.Append(Me.Page.ClientScript.GetPostBackEventReference(Me, String.Empty))            writer.AddAttribute(HtmlTextWriterAttribute.Onclick, ClientSideEventReference.ToString(), True)            MyBase.AddAttributesToRender(writer)        End Sub    End ClassEnd Namespace

 

ClientSideEventReference.Append("objImg.src= ""Images/LoadingContent.gif"";")

这句是直接取的网站根目录下Images文件夹的loading gif 图片

这个控件是根据网上别人写的单次点击按钮修改的,功能更实用

单次点击按钮的功能是，在点提交时，按钮变灰，防止用户在提交未完成时，重复点击。但是这个

控件的缺陷也是显而易见的。用户不点击该按钮，但还是可以点击界面上的其它控件，所以最彻底

的办法的就是，弹出一个遮罩层，彻底隔绝用户对界面的操作

 

这里面有一个细节要注意，动态创建一个img元素以后，要判断它的size，必须要等它加载完毕,也就是图

片加载完毕

if(objImg.readystate="complete"{   //在这里才可获取img的size} 

 

           

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