Addhandler, button.click not firing using VB.NET - asp.net

I am experiencing a problem with buttons and AddHandler. It only works if I use AddHandler Button1.click, AddressOf... in Page_load, but if I create the button dynamically in one of the sub routines, the event doesn't fire.
For example,
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True">
<asp:ListItem>1</asp:ListItem>
<asp:ListItem>2</asp:ListItem>
</asp:DropDownList>
<asp:ScriptManager id="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel id="UpdatePanel1" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="False">
<contenttemplate>
<asp:PlaceHolder id="PlaceHolder1" runat="server"></asp:PlaceHolder>
</contenttemplate>
</asp:UpdatePanel>
<asp:UpdatePanel id="UpdatePanel2" runat="server" UpdateMode="Conditional">
<contenttemplate>
<asp:Label id="Label2" runat="server" Text="Label"></asp:Label>
</contenttemplate>
</asp:UpdatePanel>
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Label1.Text = Date.Now
ScriptManager1.RegisterAsyncPostBackControl(DropDownList1)
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)
Label2.Text = "Panel refreshed at " + Date.Now.ToString()
End Sub
Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
Dim b As New Button
b.Text = "Click"
ScriptManager1.RegisterAsyncPostBackControl(b)
AddHandler b.Click, AddressOf Button1_Click
PlaceHolder1.Controls.Add(b)
UpdatePanel1.Update()
End Sub
The dropdownlist works, but the button doesn't. What am I doing wrong?

You have to regenerate your dynamically created controls on every postback (at last in Page_Load, better in Page_Init). You have to set the ID of the controls accordingly because ASP.Net needs it to identify which control caused a Postback and to handle the appropriate events.
You could save the number of created buttons in ViewState and use this to regenerate them on Page_Load. Increase the number when you add a new button. Use this number also to make the Button's ID unique(append it to the ID) to ensure that its the same on every postback.
For further informations, have a look the Page-Lifecycle and ViewState with dynamically added controls.
Edit: As Joel commented, if you only need one Button you can set it's ID statically, but you have to regenerate it on postback f.e. to handle its click-event.

Just to aid anyone who has this problem and isn't quite sure how to implement. Here's a quick example.
This example starts out by displaying a dropdownlist. When user selects something from the dropdown, another dropdownlist appears.
I typed this off the top of my head, so it MAY contain errors, but you get the idea =)
In the aspx file, add a placeholder:
And in your codebehind:
...
Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
'Store control count in viewstate
If Not IsPostBack Then ViewState("ControlCounter") = 1
'Rebuild dynamic controls on every postback so when page's life cycle hits Page_Load,
'selected values in the viewstate (asp.net default behavior) can be loaded into the dropdowns
Build_Dynamic_Controls()
End Sub
Protected Sub Build_Dynamic_Controls()
'Clear placeholder
myPlaceholder.Controls.Clear()
'This is where the control counter stored in the viewstate comes into play
For i as Integer = 0 To CInt(ViewState("ControlCounter") -1
Dim ddlDynamic as New DropDownList With {
.ID = "ddlDynamicDropdown" & i,
.AutoPostBack = True
}
'This is the event that will be executed when the user changes a value on the form
'and the postback occurs
AddHandler ddlDynamic.SelectedIndexChanged, AddressOf ddlDynamic_SelectedIndexChanged
'Add control to the placeholder
myPlaceholder.Controls.Add(ddl)
'Put some values into the dropdown
ddlDynamic.Items.Add("Value1")
ddlDynamic.Items.Add("Value2")
ddlDynamic.Items.Add("Value3")
Next i
End Sub
Protected Sub ddlDynamic_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
'When a dropdown value is changed, a postback is triggered (autopostback=true)
'The event is captured here and we add another dropdown.
'First we up the control count:
ViewState("ControlCounter") = CInt(ViewState("ControlCounter")) + 1
'Now that the "total controls counter" is upped by one,
'Let's recreate the controls in the placeholder to include the new dropdown
Build_Dynamic_Controls()
End Sub
...

Related

How do I set LinkButton Visible Property from content page

How do i set the visible property of a Link button inside update panel inside master page from a content page.
This I have done inside a click event of command button without luck
dim showLnk as Linkbutton =ctype(master.findcontrol("updatepanel1").findcontrol("lnkLogOut",LinkButton)
showLnk.visible =true.
Let's say you have this code inside the Master page:
<asp:UpdatePanel ID="updatepanel1" runat="server">
<ContentTemplate>
<asp:Panel runat="server" ID="parentPanel">
<asp:LinkButton ID="lnkLogOut" runat="server">Logout</asp:LinkButton>
</asp:Panel>
</ContentTemplate>
</asp:UpdatePanel>
To set the visibility from a content page simply do this:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Dim showLnk As LinkButton = Master.FindControl("lnkLogOut")
showLnk.Visible = False
End Sub

Find a control from an updatepanel and manipulate it

I have a .aspx page that contains a hidden panel that I need to display from a .ascx control.
On my .Click event from my button on my .ascx I have the following:
Dim myControl2 As Control = FindControl("Content1")
Dim myControl3 As Control = FindControl("keywordSearchModal")
On my .aspx I have the following:
<asp:Content ID="Content1" ContentPlaceHolderID="ContentHolder" runat="server">
<asp:Panel ID="keywordSearchModal" runat="server" Width="800px" Visible="true">
This is your modal
<asp:Button ID="OKButton" runat="server" Text="Close" />
</asp:Panel>
</asp:Content>
Both myControl2 and myControl3 contain nothing when the button is clicked.
How can I find this control from the .ascx that also happens to be an updatepanel.
UPDATE
I was able to find the control by doing the following:
Dim myPanel As Panel = Page.Master.FindControl("ContentHolder").FindControl("keywordSearchModal")
myPanel.Visible = False
Dim myControl As Control = Page.Master.FindControl("ContentHolder").FindControl("keywordSearchModal")
myControl.Visible = False
I was able to use the ContentPlaceHolderID - However now I can't change the visibility...
UPDATE II
thanks to the suggestion below I was able to capture the button click on my .aspx page. However, now just like before I can't seem to manipulate the control. In this example adding text to the panel.
Protected Sub SearchStart(ByVal sender As Object, ByVal e As EventArgs) Handles EquipmentDetails1.SearchStart
Dim newLabel As New Label
newLabel.Text = "This is a label!"
keywordSearchModal.Controls.Add(newLabel)
End Sub
Thoughts?
Here is what I've used in the past...
My user control has an imagebutton and the following in the codebehind
Public Event SearchStart As EventHandler
'This will be the event triggered when the imagebutton is clicked
Protected Sub ib_Search_Click(ByVal sender As Object, ByVal e As EventArgs) Handles ib_Search.Click
'Bubble up event to parent
RaiseEvent SearchStart(Me, e)
End Sub
Any page that uses the User Control will have the following in codebehind...
Protected Sub mc_SearchFilter_SearchStart(ByVal sender As Object, ByVal e As EventArgs) Handles mc_SearchFilter.SearchStart
'CODE that needs to be executed when search image button is clicked in my_control_SearchFilter
End Sub
Hope that helps....

How to dynamically add controls and preserve Viewstate?

I'm attempting to use Controls.AddAt(), but it apparently breaks controls at later indexes:
Here's my minimal example:
Aspx put in a form:
<asp:DropDownList runat="server" ID="ddl" />
<asp:Button Text="text" runat="server" OnClick="Unnamed2_Click" />
Code Behind:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not IsPostBack Then
ddl.Items.Add("Click the button")
'Controls.Add(New HyperLink) 'Works fine, but is put at end of collection.
'Controls.AddAt(2 ,New HyperLink) 'Is also safe but I wanted the control first
Controls.AddAt(0, New HyperLink) 'ddl loses it's item after postback
End If
End Sub
On the first postback of the page after calling AddAt, the DropDownList loses it's item. It doesn't matter what kind of control I add even HTMLControls. Viewstate is not disabled.
How do I dynamically add controls without breaking others?
If you used a PlaceHolder to add your HyperLink into, it would not mess up the rest of the page:
<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
<asp:DropDownList ID="ddl" EnableViewState="true" runat="server" />
<asp:Button ID="bn1" Text="text" OnClick="Unnamed2_Click" runat="server" />
With code like
Protected Sub Unnamed2_Click(sender As Object, e As EventArgs) Handles bn1.Click
Dim newItem = "Click the button" & DateTime.Now.ToString("HH:mm:ss")
ddl.Items.Add(newItem)
ddl.SelectedIndex = ddl.Items.Count - 1
PlaceHolder1.Controls.Add(New HyperLink With {.ID = "hyp", .Text = "Hyperlink here"})
End Sub
And always give your asp:Controls an ID if they take one.

Handling events of usercontrols within listview

I have a simple usercontrol which raises an event on button click
Public Class UcPaymentCheque
Inherits System.Web.UI.UserControl
Public Event OnCancelClick()
Private Sub btnCancelPayment_Click(sender As Object, e As System.EventArgs) Handles btnCancelPayment.Click
RaiseEvent OnCancelClick()
End Sub
End Class
This usercontrol is used within a listview
<asp:ListView ID="lvwNonTpProducts" runat="server" ItemPlaceholderID="ItemPlaceholder">
<LayoutTemplate>
<asp:PlaceHolder ID="ItemPlaceholder" runat="server" />
</LayoutTemplate>
<ItemTemplate>
<TPCustomControl:UcPaymentCheque ID="UcTPPaymentCheque" runat="server" Visible="false" />
</ItemTemplate>
</asp:ListView>
which is databound on page load
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Page.IsPostBack Then
Else
BuildPage()
End If
End Sub
At what point should add the handler? I have fiddled with the ondatabound event like so;
Private Sub lvwNonTpProducts_ItemDataBound(sender As Object, e As System.Web.UI.WebControls.ListViewItemEventArgs) Handles lvwNonTpProducts.ItemDataBound
Dim UcTPPaymentCheque = DirectCast(e.Item.FindControl("UcTPPaymentCheque"), UcPaymentCheque)
AddHandler UcTPPaymentCheque.OnCancelClick, AddressOf OnCancelClick
End Sub
but this does not work and am guess at a databound issue???
You can check out my response to a similar question here: creating and listening for events
Essentially, you want a user control to raise its own event, like this:
Partial Class myControl
Inherits System.Web.UI.UserControl
Public Event MyEvent As EventHandler
'your button click event
Protected Sub bnt_click(ByVal sender As Object, ByVal e As EventArgs)
'do stuff
'now raise the event
RaiseEvent MyEvent (Me, New EventArgs)
end sub
end class
In this example, I raise the event when the user clicks a button within the user control. You can easily raise the event anywhere, such as when the control loads, using a timer, whatever.
Then, in the main page, you want to and an event handler to the user control, like this:
<mc:myControlrunat="server" ID="myControl1" OnMyEvent="myControl_MyEvent" />
Now, in the code behind, you can add the event, like this:
Protected Sub myControl_MyEvent(ByVal sender As Object, ByVal e As EventArgs)
'do stuff
end sub
You can add the handler in the declaration of the user control in the listview, using OnCancelClick, as follows:
<asp:ListView ID="lvwNonTpProducts" runat="server" ItemPlaceholderID="ItemPlaceholder">
<LayoutTemplate>
<asp:PlaceHolder ID="ItemPlaceholder" runat="server" />
</LayoutTemplate>
<ItemTemplate>
<TPCustomControl:UcPaymentCheque ID="UcTPPaymentCheque" runat="server" Visible="false" OnCancelClick="UcTPPaymentCheque_OnCancelClick" />
</ItemTemplate>
</asp:ListView>
Where UcTPPaymentCheque_OnCancelClick is the function you should use to handle the event, in the control that contains the listview.

SelectedIndexChanged event doesn't fire

I have added the AutoPostBack = "true" attribute to the drop down list.
It doesn't work.
<asp:DropDownList CssClass="dropDownList" ID="ddlBusinessUnit"
AutoPostBack="true" runat="server" Width="250px"
OnSelectedIndexChanged="ddlBusinessUnit_SelectedIndexChanged">
</asp:DropDownList>
code behind:
Protected Sub ddlBusinessUnit_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
Response.Write("Hello")
End
How can I ensure that the event method is called?
Are you populating your Dropdownlist on every Postback?
Use IsPostBack to check whether the page is loaded for the first time or not.
If Not IsPostBack Then
BinDdlBusinessUnit()
End If

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