Here is the issue:
I have a simple ASP.NET form with 2 buttons.
One of them is created by dragging the button from the tools and the other I created directly in HTML:
<body>
<form id="Form1" method="post" runat="server">
<asp:Button OnClick="ABC" Runat="server" Text="rrr" id="Button1"></asp:Button>
<asp:Button id="Button2" runat="server" Text="Button"></asp:Button>
</form>
</body>
Button2 is created using tools and has the following Event Handler:
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Dim s As String = ""
End Sub
This "Private Event handler runs without any problem.
However for the button which is created under HTML , we have the following event handler:
Private Sub ABC(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim a As Integer = 0
End Sub
For this one I get the following complile error:
Compiler Error Message: BC30390: 'WebApplication9.WebForm1.Private Sub ABC(sender As Object, e As System.EventArgs)' is not accessible in this context because it is 'Private'.
If I change the event handler scope from Private to protected this will work. Question is why private works for one event handler but not the other one.
Basically, an aspx page is implemented as two classes. One of these classes contains your code behind code (.aspx.vb) (and, depending on which version/model of ASP.Net you're using, also some designer generated code (.aspx.designer.vb)).
The second class is created when the page is first requested (or the site is pre-compiled) and contains any inline code from the .aspx page and other code generated by ASP.Net, and includes e.g. code for any controls declared with runat="server".
This second class inherits from the first.
So, if the first class takes responsibility for hooking up its event handlers, it uses a Handles clause*:
Private Sub ABC(...) Handles Button1.Click
Button1 belongs to this class because it was put there by the designer generated code. Everything is local to this class, and so the method can be Private.
If the second class takes responsibility for hooking up an event handler, it does it by using attributes on server controls, such as here:
<asp:Button OnClick="ABC" Runat="server"
Now, unless ABC is a method declared inline inside the .aspx file, it has to be from the first class (or any class from which the first itself inherits from)
We now have a situation where code in the second class wants to refer to code in the first class. And so, the rules of .NET say that the member that it's trying to access cannot be Private.
What you shouldn't have, as you have in your question, is both classes taking responsibility for hooking up the (same) event handlers.
*It doesn't have to use a Handles clause - it could also set up the event handler using AddHandler inside e.g. the Page_Load event, or anywhere else that's appropriate. Handles is idiomatic for static controls on a page in VB. In C#, there's no equivalent to Handles, so the event handlers are hooked up with C#'s equivalent of AddHandler, +=.
Related
Lately i realized a problem in asp.net, which appears kinda strange to me.
I got an sample.aspx file:
<%# Page Language="vb" AutoEventWireup="false" CodeBehind="sample.aspx.vb" Inherits="SampleProj.sample" MasterPageFile="~/Site.Master" %>
<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">
<input type="image" id="Accept" runat="server" class="accept-btn" src="/Images/accept.png" />
</asp:Content>
And the related codebehind file sample.aspx.vb:
Public Class sample
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
'Some code here
End Sub
Private Sub Accept_ServerClick(sender As Object, e As ImageClickEventArgs) Handles Accept.ServerClick
'Some code here
End Sub
So my Problem is easily explained: Upon clicking the accept button the Accept.ServerClick event is fired as expected, but for some reason (even though the page IS NOT reloaded) the Page.Load event is fired too. This is my first asp project and maybe this is an expected behaviour, but i found neither an explanation nor a way to disable it. Any information would be appreciated.
Greeting, Ohemgi
(If you find any errors this is caused by writing this short sample. My code is compiling and running without a problem, so my question is only about the load event)
That is perfectly fine. From MSDN Documentation:
After a page has been posted back, the page's initialization events (Page_Init and Page_Load) are raised, and then control events are processed.
If you do something in the Page_Load that you don't want to do every time you click a button, just wrap it inside this condition:
if (!Page.IsPostBack)
{
// Some code here. It is executed only once.
}
You can find more information in the links below:
ASP.NET Web Server Control Event Model
ASP.NET Page Life Cycle Overview
VB.Net version
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
' Some code here. It is executed only once.
End If
End Sub
I'm using the FindControl function to look for a control on the page. It seems super simple and straight forward on MSDN but I can't get it to find the control. The page I'm using has a MasterPageFile that prepends more to the id that I give the contorl in the aspx file. A simple example that isn't working:
aspx page
<%# Page Title="Inventory Control Test" Language="VB" AutoEventWireup="false" MasterPageFile="~/Site.master" CodeFile="Default2.aspx.vb" Inherits="Sales_ajaxTest_Default2" %>
<asp:Content ID="conHead" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="conBody" ContentPlaceHolderID="MainBody" Runat="Server">
<asp:Button ID="saveAllBtn" runat="server" Text="Save All" />
</asp:Content>
code behind
Partial Class Sales_ajaxTest_Default2
Inherits System.Web.UI.Page
Protected Sub saveAllBtn_Click(sender As Object, e As System.EventArgs) Handles saveAllBtn.Click
Dim myControl1 As Control = FindControl("ctl00_MainBody_saveAllBtn")
If (Not myControl1 Is Nothing) Then
MsgBox("Control ID is : " & myControl1.ID)
Else
'Response.Write("Control not found.....")
MsgBox("Control not found.....")
End If
End Sub
End Class
I get that msgbox isn't a web thing I'm just using it for this example.
If i use "saveAllBtn", which is the id given to the control, in the FindControl I get "control not found". If I try this, on a stand alone page without a masterpage it works fine.
If I inspect the element using chrome I find that the ID of the button has been changed to "ctl00_MainBody_saveAllBtn" but if I use that in the FindControl I still get "control not found"
When you use FindControl you would specify the "server ID" (what you named it) of the control, not the final rendered "client ID" of the control. ex:
Dim myControl as Control = MainBody.FindControl("saveAllBtn")
However, in your specific example, since you are in the saveAllBtn.Click event, the control you are looking for is actually the sender parameter (because you clicked on that button to trigger the event you are in) ex:
Dim myControl as Button = CType(sender, Button)
If you just want to find saveAllBtn control, wweicker's second method using CType(sender, Button) is the prefer one.
However, if you want to find other control by name, you cannot use just FindControl. You need to find the control recursively, because it is nested inside other controls.
Here is the helper method -
Protected Sub saveAllBtn_Click(sender As Object, e As EventArgs)
Dim button = TryCast(FindControlRecursive(Me.Page, "saveAllBtn"), Button)
End Sub
Public Shared Function FindControlRecursive(root As Control, id As String) As Control
If root.ID = id Then
Return root
End If
Return root.Controls.Cast(Of Control)().[Select](Function(c) FindControlRecursive(c, id)).FirstOrDefault(Function(c) c IsNot Nothing)
End Function
Note: My VB code might be a bite weird, because I wrote in C# and converted to VB using converter.
FindControl does not work recursively. You must start at one point (Me, for example), and if that is not the control your looking for, search the Controls collection of your starting point. And so forth.
I have a VB ASP.NET web application with two User Controls each containing one text input. There are two submit buttons each corresponding to one of the User Controls.
Clicking a button adds an instance of its corresponding User Control. For the most part this works except that in a specific scenario the IDs of the textboxes get mixed up thereby mixing up previously entered values.
The problem scenario is as follows:
1) Click the second button (the Add Approver button) twice and enter some values in the two resulting textboxes (for ease of analysis make the values different).
2) Click the first button (the Add Document button) once. (There is no need to add any value in the resulting textbox here.)
At this point everything appears correct. Viewing the page source, I see that the two "Approver" textboxes have IDs of ctl02_txtApprover and ctl03_txtApprover and the one "Document" textbox has an ID of ctl04_txtDocument.
Click the first button (the Add Document button) again.
At this point the value in the first "Approver" textbox disappears. The value in the second "Approver" textbox migrates to the first "Approver" textbox. Viewing the page source, the IDs for the two "Approver" textboxes have changed to ctl03_txtApprover and ctl04_txtApprover. The migrated values make sense considering that the textbox IDs have changed. In other words, the ViewState appears correct but the control IDs are incorrect.
I have made the code as simple as I can and have posted it here.
Default.aspx
<%# Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="WebApplicationUserControlTest._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:PlaceHolder ID="phDocument" runat="server" />
<asp:Button ID="btnAddDocument" runat="server" Text="Add Document" />
<br /><br />
<asp:PlaceHolder ID="phApprover" runat="server" />
<asp:Button ID="btnAddApprover" runat="server" Text="Add Approver" />
</form>
</body>
</html>
Default.aspx.vb
Public Class _Default
Inherits System.Web.UI.Page
Private Const VIEWSTATE_DOCUMENT_COUNT As String = "DocumentCount"
Private Const VIEWSTATE_APPROVER_COUNT As String = "ApproverCount"
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not IsPostBack Then
ViewState(VIEWSTATE_DOCUMENT_COUNT) = 0
ViewState(VIEWSTATE_APPROVER_COUNT) = 0
Else
're-display any preexisting dynamic sections on postback
AddAllDocumentInfoSections()
AddAllApproverSections()
End If
End Sub
Protected Sub btnAddDocument_Click(sender As Object, e As EventArgs) Handles btnAddDocument.Click
ViewState(VIEWSTATE_DOCUMENT_COUNT) += 1
AddDocumentSection()
End Sub
Protected Sub btnAddApprover_Click(sender As Object, e As EventArgs) Handles btnAddApprover.Click
ViewState(VIEWSTATE_APPROVER_COUNT) += 1
AddApproverSection()
End Sub
Private Sub AddAllDocumentInfoSections()
For i As Integer = 0 To ViewState(VIEWSTATE_DOCUMENT_COUNT) - 1
AddDocumentSection()
Next
End Sub
Private Sub AddAllApproverSections()
For i As Integer = 0 To ViewState(VIEWSTATE_APPROVER_COUNT) - 1
AddApproverSection()
Next
End Sub
Private Sub AddDocumentSection()
Dim c As UserControl = LoadControl("~/Document.ascx")
phDocument.Controls.Add(c)
End Sub
Private Sub AddApproverSection()
Dim c As UserControl = LoadControl("~/Approver.ascx")
phApprover.Controls.Add(c)
End Sub
End Class
Document.ascx
<%# Control Language="vb" AutoEventWireup="false" CodeBehind="Document.ascx.vb" Inherits="WebApplicationUserControlTest.Document" %><asp:TextBox ID="txtDocument" runat="server" /><br /><br />
Approver.ascx
<%# Control Language="vb" AutoEventWireup="false" CodeBehind="Approver.ascx.vb" Inherits="WebApplicationUserControlTest.Approver" %><asp:TextBox ID="txtApprover" runat="server" /><br /><br />
I am using Visual Studio 2010. The Target Framework is 4.0. I have tried changing the clientIDMode but this does not seem to make a difference. Have I run into a bug with .NET or is there something wrong with my code?
There is something wrong with your code.
If you dynamically add controls to the same naming container in a control tree, then you need to add them in the same order after each postback.
In your case, you're not doing this.
At your step 2, you have added three controls in this order:
Approver 1 (AddAllApproverSections)
Approver 2 (AddAllApproverSections)
DocumentInfo 1 (btnAddDocument_Click)
But then after the postback, you regenerate them in the following order:
DocumentInfo 1 (AddAllDocumentInfoSections)
Approver 1 (AddAllApproverSections)
Approver 2 (AddAllApproverSections)
Hence the control ids aren't the same, and the problems you're seeing.
One solution might be to store additional information in ViewState that represents the order the controls were added, so that you can recreate them in the same order.
But I'd probably be inclined to go for a different approach, for example put the DocumentInfo sections into the template of a Repeater, and the Approver sections into a second Repeater. Each Repeater would be data bound to a suitable collection, and adding an item (Approver or DocumentInfo) would be achieved by adding an element to the relevant collection and calling DataBind.
The problem here is that you are modifying the Controls collection and ViewState after they have been initialized. You should never dynamically add controls in the Page Load event.
You need to add your controls in the Page_Init stage of the Page life cycle, and remove the code from the else statement in your Page_Load event. Your new Page_Init event would look like this:
Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
AddAllDocumentInfoSections()
AddAllApproverSections()
End Sub
I believe you may have to change the way you're storing the "count" for these controls, as the View State information is not yet available at this stage. I would just store it as a Session variable, in that case. You'd just need to change your reference to "ViewState" throughout that code sample with "Session", like this:
Private Sub AddAllDocumentInfoSections()
For i As Integer = 0 To Session(VIEWSTATE_DOCUMENT_COUNT) - 1
AddDocumentSection()
Next
End Sub
I have a system setup as follows:
User Control Called "Main" when I click a button in "Main" another user control (user control "A", user control "B", user control "C") is populated inside a placeholder of "Main" depending on some logic either A,B, or C is populated.
User controls A,B,C have many buttons on them as well. They Also have a placeholder to contain either user control x, user control y, user control z depending what is clicked inside user control "A" for example.
Main loads controls (A,B, or C) into its placeholder no problem, but when I click a button in A,B,or C to load their placeholder with x,y, or z the whole control (A,B, or C) dissappears.
I understand this has to do with viewstate not holding dynamic controls during a postback. So what I did was explictly called viewstate on the controls loaded into main (A,B,C). when they are loaded I save an entry of what was loaded like this ViewState("lastLoaded")='A' for example. When a postabck occurs (i.e. clicking a button in A) I reload the whole control A.
This is what happens:
I click a button in user control "A"
Postback occurs
User control "A" is reloaded because of the viewstate("lastloaded")
Then I have to click the button in "A" again at that time the button_click event fires
Can someone please help me fix this.
'Here is Main.ascx
Partial Class Main
Inherits System.Web.UI.UserControl
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
ViewState("name") = "ControlA2.ascx"
AddControl(ViewState("name").ToString())
End Sub
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If ViewState("name") <> String.Empty Then
AddControl(ViewState("name").ToString())
End If
End Sub
Public Sub AddControl(ByVal name As String)
PlaceHolder1.Controls.Clear()
Dim toAdd As Control = LoadControl(name)
PlaceHolder1.Controls.Add(toAdd)
End Sub
Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click
ViewState("name") = "ControlB.ascx"
AddControl(ViewState("name").ToString())
End Sub
End Class
'Here is Main designer
Main
asp:Button ID="Button1" runat="server" Text="Add Control A"
asp:Button ID="Button2" runat="server" Text="Add Control B"
asp:PlaceHolder ID="PlaceHolder1" runat="server">
'Here is ControlA2.ascx
Partial Class ControlA2
Inherits System.Web.UI.UserControl
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
PlaceHolder1.Controls.Clear()
Dim toAdd As Control = LoadControl("ControlX.ascx")
PlaceHolder1.Controls.Add(toAdd)
End Sub
End Class
'Here is ControlA2 designer
I am Control A
Add Control X
asp:Button ID="Button1" runat="server" Text="Add Control X"
asp:PlaceHolder ID="PlaceHolder1" runat="server"
/asp:PlaceHolder
'Here is ControlB.ascx
Partial Class ControlA2
Inherits System.Web.UI.UserControl
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
PlaceHolder1.Controls.Clear()
Dim toAdd As Control = LoadControl("ControlZ.ascx")
PlaceHolder1.Controls.Add(toAdd)
End Sub
End Class
'Here is ControlB designer
I am Control B
Add Control Z
asp:Button ID="Button1" runat="server" Text="Add Control Z"
asp:PlaceHolder ID="PlaceHolder1" runat="server" /asp:PlaceHolder
'Here is ControlX.designer
asp:Label ID="Label1" runat="server" Text="Label">I AM CONTROL X /asp:Label
'Here is ControlZ designer
asp:Label ID="Label1" runat="server" Text="Label">I AM CONTROL Z /asp:Label
I've created a project based on your code and I've managed to recreate the issue.
When I initially run it and click on the Add control A button the Main control will load Control A and note this in the viewstate. Control A's button to add Control X will now appear with an id of Main1_ctl00_Button1. When clicking on this button Main's page load will add Control A back to it's placeholder and Control A's button click event will fire. If you now click Main's Control A button again the problem arises. Main's page load method will look at the Viewstate and add control A to the placeholder. Then Main's button click event will then fire clearing the placeholder and re-adding control A. When the form is displayed Control A's button to add Control X will now have an id of Main1_ctl01_Button1 as it was the second control to be generated in the code behind. Now when you click on the button to add control x Main's page load will add Control A again but as it's id will be Main1_ctl00_Button1 and the click event came from a button with an id of Main1_ctl01_Button1 the event will not fire.
To fix this you will have to avoid the duplication of control creation the second time around. You could do this by checking the requests form collection during the page load to see which button was pressed although this is not a very elegant solution. You will need to ensure that the buttons on the Main control have a unique text value for this to work.
Hopefully someone else may be able to come up with a more elegant solution:
Dim mainButtonClick = False
For index As Integer = 0 To Request.Form.Count
If Request.Form(index) = "Button A" Or Request.Form(index) = "Button B" Then
mainButtonClick = True
End If
Next
If Not IsPostBack And Not mainButtonClick And ViewState("name") <> String.Empty Then
AddControl(ViewState("name").ToString())
End If
Please excuse any errors in this code as I am not a VB.NET programmer.
I've got two aspx pages which are very similar and have various identical functions in the code behind. I'd like to create a base class which both the code behind classes derive from. Is it possible for the base class to access the controls on the aspx page. For instance:
class base
inherits System.Web.UI.Page
Sub prepareScreen()
'txtName is a text box on the aspx page
Me.txtName.text = "George"
end sub
end class
class codeBehind
inherits base
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
prepareScreen()
end sub
end class
Somewhat understandably the code fails to compile with:
'txtName' is not a member of 'clsbase'
Is it possible to link the two together?
You need to declare the control as a property of the base class. Then in the ASP markup, use the CodeFileBaseClass attribute.
The MSDN reference is no longer available.
class base
inherits System.Web.UI.Page
Protected Property txtName() As TextBox
Sub prepareScreen()
'txtName is a text box on the aspx page
Me.txtName.text = "George"
end sub
end class
class codeBehind
inherits base
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
prepareScreen()
end sub
end class
<%# page CodeFileBaseClass="base" inherits="codebehind" ... %>
It would be better if you refactor your code, so that you have no need to do something like this.
One better idea will be if you create a virtual method in the base class, which you can override in your child page(s), and set the value of your textbox, as you'll have an easy access to the textbox.
You could use FindControl, eg.
TextBox txtName=FindControl("txtName");
which would find the control on the rendered page even though it was rendered by the descendant class. Though this is breaking the point of OO and separation of function/data somewhat.
You can use ((TextBox)Page.FindControl("txtName")) to get the textbox. Be careful because if you use this base class else where the control might not exist
In response to your clarification:
You could Create a property:
protected TextBox txtName
{
get{return (TextBox)Page.FindControl("txtName");}
set{Page.FindControl("txtName") = vale;}
}
Or Create a Virtual property:
protected virtual TextBox txtName{get;set;}
In this case you would have to override it at your main class
protected override TextBox txtName{/*same as above*/}