Call C# code behind function from programatically created button - c#

In my webform I created button from my code behind:
Button btnShowCase = new Button();
btnShowCase.ID = "btnShowCase_" + ticketNumber;
btnShowCase.CssClass = "BtnShowCase";
btnShowCase.Text = "Display";
btnShowCase.OnClientClick = "ShowCase";
On client click I want to execute function
protected void ShowCase(object sender, EventArgs e)
{
Do something
}
OnClientClick do not call ShowCase. What I am doing wrong?

Instead of
btnShowCase.OnClientClick = "ShowCase";
Try
btnShowCase.OnClick += ShowCase;
ClientClick invokes Javascript that runs within the browser; the string argument is the name of a Javascript function. Click causes a postback and invokes a server-side method; the argument is a method that matches the delegate for the event type.

OnClientClick is an event handler, and should be set like this:
btnShowCase.OnClientClick += "ShowCase";
instead of
btnShowCase.OnClientClick = "ShowCase";

Related

Dynamic button in asp.net - EventHandler is not fired

I created a button from code behind:
Panel dynamicPanel = new Panel();
Button dynamicButton = new Button();
dynamicButton.Text = "View";
dynamicButton.Click += new EventHandler(dynamicButton_Click);
dynamicPanel.Controls.Add(dynamicButton);
dynamicDiv.Controls.Add(dynamicPanel);
and the OnClick method:
protected void dynamicButton_Click(object sender, EventArgs e)
{
Response.Write("view button response");
string script = "alert(\"view clicked.\");";
ScriptManager.RegisterStartupScript(this, GetType(),
"ServerControlScript", script, true);
}
When I click the button, there is postback (IsPostback with Javascript alert) but the EventHandler is not fired. I can say that content that was visible on the page disappears if that is a clue.
I need to create this in a custom protected void method.
Your code looks a bit weird to me, but as for the problem "When I click the button, the method is not fired": Try renaming the method dynamicREGButton_Click() to dynamicButton_Click().
I assume you have a method dynamicButton_Click() in your code already; otherwise, you could not compile. However, the method you register via dynamicButton.Click += new EventHandler(...); is the method you call. The code you showed us doesn't match in that regard.

linkbuttons postback before executing click event code?

I am trying to add a basic switch to my site in order to switch between static and responsive layouts.
I have two linkbuttons at the bottom of my page:
<div id="toggleView">
<asp:linkbutton ID="lbtnMobile" runat="server" Visible="false">Switch to Mobile site</asp:linkbutton>
<asp:linkbutton ID="lbtnFull" runat="server" >Switch to Full site</asp:linkbutton>
</div>
They both have a very similar OnClick event.
protected void lbtnFull_Click(object sender, EventArgs e)
{
c.ViewChange = true;
Session["Customer"] = c;
}
protected void lbtnMobile_Click(object sender, EventArgs e)
{
c.ViewChange = false;
Session["Customer"] = c;
}
The events should set a boolean in a class file (User.vb) between true or false and then save the session, on postback the Page_Load event is supposed to read this boolean and use it to adjust the Viewport meta tag:
protected void Page_Load(object sender, System.EventArgs e)
{
//Other Stuff in here, irrelevant to current question
HtmlMeta view = new HtmlMeta();
view.Name = "viewport";
if (c.ViewChange = false)
{
view.Content = "width=device-width, initial-scale=1";
lbtnFull.Visible = true;
lbtnMobile.Visible = false;
}
else
{
view.Content = "width=1040px, initial-scale=1";
lbtnFull.Visible = false;
lbtnMobile.Visible = true;
}
MetaPlaceHolder.Controls.Add(view);
}
However, when I click on the "Switch to Full Site" linkbutton, the page will postback but nothing will have changed. Does the postback get triggered too early somehow?
The page load event will happen BEFORE your click event. Reference this here.
This means your check for the ViewChange will happen before you set it in the OnClick handler.
You should change
if (c.ViewChange = false)
to
if (c.ViewChange == false)
for something to happen. But I think it won't be what you expect. Because page_load is executed before click event. You may move some code from page_load to click event handlers.
When ever you postback the Page_Load always get called. So, the code mentioned inside Page_Load would always get executed.
protected void Page_Load(object sender, System.EventArgs e)
{
... All your mentioned code will be executed.
}
Therefore, you won't find any change in your HTML page currently viewed in a browser because at postback initial content also got executed. You need to wrap your content inside !IsPostBack to make it work properly.
Thus, modify you code in following way.
protected void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostback)
{
... All your mentioned code will be executed during normal load.
}
}
Also, you need to add some extra code in LinkButton click event i.e. what to show and what to hide.
Firstly your implementation in the Page_Load isn't very clear.
Nevertheless this is what I recommend, from what I've understod:
As the page load will get executed before the post-back event like the buton or link click, you need persist the value of the class object
Make a protected property of type of your class (where you store/manage the ViewChange atribute)
The property should internally (in the get & set), hold/persist the value in session/viewstate (similar to what you've written)
The setting and reading should only be by referring the property directly (and not how you've done the click-event)
On clicking of the button and post setting the new value, you will have to redirect to the same page, as only then the Page_Load event will get the new boolean value that you've just changed in the click-event; (Page_Load occurs befoer the any other post-back event)
An alternative to the fresh redirection is that, you could make a function that has the view changing logic (as depicted in your Page_Load code), and this function should be called on your button/link click event (post boolean value change) and also in the Page_Load event, but within the "!IsPostBack" block
Hope this helps you.

How to create an onClick eventHandler for a dynamically created button

Currently, I am doing a project for students' hostel and now I have to implement some search strategies about students.Here I have to create a button dynamically when the user clicks on the another server button in .aspx page and accordingly I have to create the onclick event handler for the newly created button. The code-snippet that I used is:
protected void btnsearchByName_Click(object sender, EventArgs e)
{
TextBox tbsearchByName = new TextBox();
Button btnsearchName = new Button();
tbsearchByName.Width = 250;
tbsearchByName.ID = "tbsearchByName";
tbsearchByName.Text = "Enter the full name of a student";
btnsearchName.ID = "btnsearchName";
btnsearchName.Text = "Search";
btnsearchName.Click += new EventHandler(this.btnsearchName_Click);
pnlsearchStudents.Controls.Add(tbsearchByName);
pnlsearchStudents.Controls.Add(btnsearchName);
}
protected void btnsearchName_Click(object sender, EventArgs e)
{
lblsearch.Text = "btnsearchName_Click event fired in " + DateTime.Now.ToString();
}
Here, the problem is newly created eventHandler doesnot get fired. I have gone through this site and looked several questions and answers and also gone through the page life-cycle and they all say that the dynamic button should be on Init or Pre_init, but my problem is I have to create it when another button is clicked, how can it be possible?
You need to add the click handler for the button on every postback.
you could look for the button in the search students panel on page load or try the page OnInit() method to add the handler when its created.
Also check here:
Dynamically added ASP.NET button click handler being ignored
and here:
asp.net dynamically button with event handler
and here:
asp:Button Click event not being fired
(all of which give similar suggestions)
Try this http://msdn.microsoft.com/ru-ru/library/system.web.ui.webcontrols.button.command(v=vs.90).aspx
btnsearchName.Command += new CommandEventHandler(this.btnsearchName_Click);
btnsearchName.CommandName = "Click";
You need to recreate the button and attach the event handler every time. For this, create a list of button and save it on session. On page load, go through the List and create the button every time
public Button create_button()
{
btnsearchName.ID = "btnsearchName";
btnsearchName.Text = "Search";
btnsearchName.Click += new EventHandler(this.btnsearchName_Click);
return btnsearchName;
}
public TextBox create_textbox()
{
TextBox tbsearchByName = new TextBox();
Button btnsearchName = new Button();
tbsearchByName.Width = 250;
tbsearchByName.ID = "tbsearchByName";
tbsearchByName.Text = "Enter the full name of a student";
return tbsearchByName;
}
protected void btnsearchByName_Click(object sender, EventArgs e)
{
TextBox tbsearchByName = create_textbox();
Button btnsearchName = create_button();
//add to panels
pnlsearchStudents.Controls.Add(tbsearchByName);
pnlsearchStudents.Controls.Add(btnsearchName);
//add to session
List<Button> lstbutton = Session["btn"] as List<Button>
lstbutton.add(btnsearchName);
//similarly add textbox
//again add to session
Session["btn"] = lstbutton
}
public override page_load(object sender, eventargs e)
{
//fetch from session, the lstButton and TextBox and recreate them
List<Button> lstbutton = Session["btn"] as List<Button>;
foreach(Button b in lstbutton)
pnlsearchStudents.Controls.Add(b);
//similar for textbox
}
I am not sure but may be you have to override the OnInit() method like this.
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
}
You just need to add this code on ready state of jquery code and it will work fine for the dynamic button too
$(document).ready(function(){
$('input#tbsearchByName').click(function(){
// code goes here
});
});

Can't call Click Event on dynamic button

I want to create a method in code behind that creates a button and places it in a PlaceHolder. I want this button to have a Click event.
After calling the "test" method button is placed correctly but the click event is not called.
private void test()
{
Button linkBtn1 = new Button();
linkBtn1.Text = "linkBtn1";
linkBtn1.OnClientClick = "return false;";
linkBtn1.Click += new EventHandler(linkBtn1_Click);
PagesPlaceHolder.Controls.Add(linkBtn1);
}
void linkBtn1_Click(object sender, EventArgs e)
{
throw new NotImplementedException();
}
Removing the OnClientClick = "return false;" is necessary but not sufficient to get this to work. If you want the event handler on the dynamically added button to be triggered, you'll need to add this button every time the page loads.
One simple way would be to save the fact that the button has been added in ViewState, and then check that on PageLoad, and re-add the button if needed.
Here's a sample that works for me (and throws the exception when clicked)
protected void Page_Load(object sender, EventArgs e)
{
//if the button was added previously, add it again
if (ViewState["Added"] != null && (bool)ViewState["Added"])
addButton();
}
//this is the method that adds the button
protected void add_Click(object sender, EventArgs e) {
ViewState["Added"] = true;
addButton();
}
private void addButton() {
Button linkBtn1 = new Button();
linkBtn1.Text = "linkBtn1";
linkBtn1.Click += new EventHandler(linkBtn1_Click);
placeholder1.Controls.Add(linkBtn1);
}
void linkBtn1_Click(object sender, EventArgs e) {
throw new Exception("Button Click Event Triggered. Hello yellow screen!!!");
}
As #oleksii points out, have the clientside code is returning false so the form never gets submitted. You need to comment this out, then your event handler should fire.

disable "cause validation" for dynamically created buttons

I am creating the same button twice: once on Page_Load, and another on: Page_PreRender.
I expected to see the same behavior, however, the buttons created on Page_PreRender doesn't work the way intended. (i.e. property "causeValidation" remains true).
"I want to disable "causeValidation" for the button in page_preRender, and i want it there in PreRender. Also, I want the Button_Click function to execute for both buttons, currently it does only for button created on "Page_load" ".
I am looking for a solution or an explanation for this behavior.
Thank You.
Take a look at the code:
protected void Page_Load(object sender, EventArgs e)
{
form1.Controls.Add(GetButton("Button1", "Click"));
}
protected void page_PreRender(object sender, EventArgs e)
{
form1.Controls.Add(GetButton("Button3", "Click"));
}
private Button GetButton(string id, string name)
{
Button b = new Button();
b.Text = name;
b.ID = id;
b.CausesValidation = false;
b.Click += new EventHandler(Button_Click);
b.OnClientClick = "ButtonClick('" + b.ClientID + "')";
return b;
}
protected void Button_Click(object sender, EventArgs e)
{
ClientScript.RegisterClientScriptBlock(this.GetType(), ((Button)sender).ID, "<script>alert('Button_Click');</script>");
Response.Write(DateTime.Now.ToString() + ": " + ((Button)sender).ID + " was clicked");
}
and here is the javascript:
<script type="text/javascript">
function ButtonClick(buttonId) {
alert("Button " + buttonId + " clicked from javascript");
}
</script>
Update:
let me add this: Both buttons execute the client's script. This means that buttons are created. "see function GetButton() ".
Also, the reason why i have the button created "on preRender" instead of "on Page_Load" is that: if i have a form used to enter data into a table dynamically, and i add the data on button click, the the page will PostBack first, then execute the event handler, (i.e the data is added to the table but will show on NEXT postBack). So, PreRender is used to show the table AFTER it is updated by the button_click event.
I hope this addition is useful
As you see from this image, that represents asp.net page life cycle (copied from MSDN), Event Handling precedes PreRender. So, in order to fire Button_Click the button itself has to be created before the Event Handling. Page PreInit is a preferred place to add dynamic controls.
you can see it yourself, just add breakpoints at Page_Load, Page_PreRender, Button_Click. notice the order there are triggered?
Check asp.net page lifecycle: events are handled after page load and before PreRender.
ASP.NET cannot handle an event involving a control that does not yet exists.

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