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Invoke OnClientClick of button in code behind

I have an button in my aspx web page, which should be 'clicked' in my code behind c# code. The OnClientClick method then call a JS confirm dialog box and so the btn_Click function only get executed when user click 'OK'...
This is my code so far:
Variante 1
aspx:
<asp:Button runat="server" ID="btnConfirm" Text="Confirm" OnClick="btnConfirm_Click" />
aspx.cs:
protected void Page_Load(object sender, EventArgs e)
{
// set OnClientClick
btnConfirm.OnClientClick = "confirm('Save in DB?');";
// invoke method
Type t = typeof(System.Web.UI.WebControls.Button);
object[] p = new object[1];
p[0] = EventArgs.Empty;
MethodInfo m = t.GetMethod("OnClick", BindingFlags.NonPublic | BindingFlags.Instance);
m.Invoke(btnConfirm, p);
}
protected void btnConfirm_Click(object sender, EventArgs e)
{
//save something in database
}
Got code samples by: http://forums.asp.net/t/1046550.aspx?How+do+you+raise+a+button+click+event+from+outside+the+button+
I want to call the OnClientClick method, but when I replace 'OnClick' with 'OnClientClick' this error appear:
System.NullReferenceException was unhandled by user code
Message=Object reference not set to an instance of an object.
Edit:
Variante 2:
I tried to rewrite my program like this:
aspx:
<script language="javascript">
function invokeButtonClick() {
document.getElementById("btnConfirm").click();
}
function Validate() {
return confirm('Save in db?');
}
</script>
<asp:Button runat="server" ID="btnConfirm" Text="Confirm" OnClick="btnConfirm_Click" OnClientClick="return Validate();" />
aspx:cs:
protected void Page_Load(object sender, EventArgs e)
{
ScriptManager.RegisterStartupScript(this, GetType(), "InvokeButton", "invokeButtonClick();", true);
}
protected void btnConfirm_Click(object sender, EventArgs e)
{
// save something in database
}
But then the page postback before my btnConfirm_Click function get called...
Thanks,
Michael

If OnClientClick has a return value of true then the codebehind OnClick event will fire. If OnClientClick is returned false then it won't.
If OnClientClick doesn't return anything the codebehind event will fire regardless. So you want..
<asp:Button runat="server" ID="btnConfirm" Text="Confirm" OnClick="btnConfirm_Click" />
<script language="javascript">
function Validate() {
return confirm('Save in db?');
}
</script>
Codebehind:
protected void Page_Load(object sender, EventArgs e)
{
// set OnClientClick
btnConfirm.OnClientClick = "return Validate();";
}
protected void btnConfirm_Click(object sender, EventArgs e)
{
//save something in database
}
UPDATE:
This post just came to my attention, don't know why I didn't include it in my original post but you can use 'OnClientClick' in the aspx tag:
<asp:Button runat="server" ID="btnConfirm" OnClientClick="return Validate();" Text="Confirm" OnClick="btnConfirm_Click" />
<script language="javascript">
function Validate() {
return confirm('Save in db?');
}
</script>

You need to Add both the events on the button click. OnClientClick handles the Client side script code and OnClick handles the server side event calling.
So add both events and there handlers. The NullReferenceException you are getting because of that.
<asp:Button runat="server" ID="btnConfirm" Text="Confirm" OnClick="btnConfirm_Click" OnClientClick="return Validate();" />
and in your javascript code can be
function Validate(){
if (valied())
return true;
return false;
}

100% code behind confirmation! Sometiems its so annyoing to Code behind or Server side confirmation in asp.net when you want to Delete or Update something, I got its solution after a long search as below:
<asp:Button ID="btnSave" runat="server" Text="Save" OnClientClick="return confirm('Are you sure to BLOCK this customer ?')" OnClick="btnSave_Click" />
Now whenever you will click this button it 'll ask to confirm, if you 'll select "NO" page will not post and if you select "Yes" then page will post and your button click event will be fire... like below
Code behind:
protected void Page_Load(object sender, EventArgs e)
{
}
// Before coming here,,,there will be confirmation
protected void btnSave_Click(object sender, EventArgs e)
{
GetCustomerInfo();
}

How can I pass a value from a Button_Click event to Page_Load

It seems I am struggling with the order of the page life cycle. Based on the user selecting button 1 or 2, I need to have respective controls added dynamically during the Page_Load event. My problem is when a button is clicked the Page_Load event is executed before Button_Click event code is read. There for my variable "doWhat" is not assigned a value until after the Page_Load event. How can I have the "doWhat" variable assigned a value to be read during the Page_Load?
Below is asp.net form code for the two buttons:
<form id="form1" runat="server">
<div>
<asp:Button ID="Button1" runat="server" Text="Button 1" onclick="Button_Click" />
<asp:Button ID="Button2" runat="server" Text="Button 2" onclick="Button_Click" />
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>
</div>
</form>
Below is the code behind:
int doWhat;
protected void Page_Load(object sender, EventArgs e)
{
doWhat = Convert.ToUInt16(ViewState["doWhat"]);
if (doWhat == 1)
{
// code to dynamically load group 1 controls
}
else
{
// code to dynamically load group 2 controls
}
Label1.Text = Convert.ToString(doWhat);
}
protected void Button_Click(object sender, EventArgs e)
{
Button btn = sender as Button;
if (btn.ID == "Button1")
{
doWhat = 1;
}
else
{
doWhat = 2;
}
ViewState.Add("doWhat", doWhat);
}

If you are comfortable with javascript then you can achieve it by making following changes in your design and code. Add a hidden field in your aspx page. Your HTML code should be like this.
<form id="form1" runat="server">
<div>
<asp:Button ID="Button1" runat="server" Text="Button 1" OnClick="Button_Click" OnClientClick="return doWhatAction(1);" />
<asp:Button ID="Button2" runat="server" Text="Button 2" OnClick="Button_Click" OnClientClick="return doWhatAction(2);" />
<asp:Label ID="Label1" runat="server" Text=""></asp:Label>
<asp:HiddenField ID="HiddenField1" Value="1" runat="server" />
<script type="text/javascript">
var doWhatAction = function (actionIndex) {
//alert(actionIndex);
document.getElementById("<%=HiddenField1.ClientID%>").value = actionIndex;
return true;
}
</script>
</div>
</form>
And your code will be something like...
int doWhat;
protected void Page_Load(object sender, EventArgs e)
{
//doWhat = Convert.ToUInt16(ViewState["doWhat"]);
doWhat = Convert.ToUInt16(HiddenField1.Value);
if (doWhat == 1)
{
// code to dynamically load group 1 controls
}
else
{
// code to dynamically load group 2 controls
}
Label1.Text = Convert.ToString(doWhat);
}
protected void Button_Click(object sender, EventArgs e)
{
//Do Nothing
//Button btn = sender as Button;
//if (btn.ID == "Button1")
//{
// doWhat = 1;
//}
//else
//{
// doWhat = 2;
//}
//ViewState.Add("doWhat", doWhat);
}

You can use jquery or javascript i this case.
Took on hidden variable in form
initialize it on click event of button in javascript
Read value of hidden variable in page load
<head >
<title>Hidden Variable</title>
<script type="text/javascript">
function SetHDNValue()
{
var hdnControlID = '<%= hdnControl.ClientID %>';
document.getElementById(hdnControlID).value=1;
}
</script>
</head>
<body >
<form id="form1" runat="server">
<div>
<input id="hdnControl" type="hidden" runat="server" />
<asp:Button ID="btnJSValue" Text="Click" runat="server" OnClientClick="SetHDNValue()"
/>
</div>
</form>
</body>
And in code behind file hdnControl.value

Since long ago I am not working with asp.net forms. And forgot doing things.But I found how you can do. As on stackoverflow link like answers is wrong. I copied main statements from the link which indicate how post-back events works and how you can use it for your purpose. For more http://aspsnippets.com/Articles/How-to-find-the-control-that-caused-PostBack-in-ASP.Net.aspx
All controls accept Button and ImageButton use JavaScript for causing a postback. To enable postback on these controls one has to set AutoPostBack property to true.
When you set this property to true, __doPostBack function is called on event which causes a postback.
The __doPostBack function is not visible in Source of the page until you place a LinkButton or set AutoPostBack to true for any of the above discussed controls.
Here is how generated __doPostBack looks:
<script type = "text/javascript">
function __doPostBack(eventTarget, eventArgument) {
if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
theForm.__EVENTTARGET.value = eventTarget;
theForm.__EVENTARGUMENT.value = eventArgument;
theForm.submit();
}
}
</script>
The __doPostBack function simply stores the below two arguments in two hidden fields
eventTarget – The name of the control that caused the postback
eventArgument – The argument to be sent to server.
In two hidden fields which also appear only when AutoPostBack is set to true
Finally, here is how you can distinguish by getting control's ID that caused the postback :
if (IsPostBack)
{
string CtrlID = string.Empty;
if (Request.Form["__EVENTTARGET"] != null &&
Request.Form["__EVENTTARGET"] != string.Empty)
{
CtrlID = Request.Form["__EVENTTARGET"];
/****implement Your logic depending on control ID****/
}
}

ASP - file upload in single step

Browse and Upload with using asp:FileUploadcontrol is working perfectly fine.
But It is two step process. First we have to browse and then select the file.
I want it working in single step So for making it single step I tried the following code:
protected void Button1_Click(object sender, EventArgs e)
{
//to launch the hidden fileupload dialog
ClientScript.RegisterStartupScript (GetType(),
"hwa", "document.getElementById('fileupload').click();", true);
//Getting the file name
if (this.fileupload.HasFile)
{
string filename = this.fileupload.FileName;
ClientScript.RegisterStartupScript(GetType(), "hwa", "alert('Selected File: '" + filename + ");", true);
}
else
{
ClientScript.RegisterStartupScript(GetType(), "hwa", "alert('No FILE has been selected');", true);
}
}
In this code, there is one fileUpload control that is being invoked on Button1_Click. Ideally it should execute the first line then A file Upload control should be shown and after selecting a file or canceling the dialog, flow should go to next line. But dialog is showing up after full function execution finishes.
Because of this asynchronous or not expected execution flow if (this.fileupload.HasFile) is returning false(because user has not been asked to select any file yet) and I am not getting the selected file name.
Can we modify this code to achieve file upload in single step? Or if any other way is possible to do this?
Note- I have asked not to use window forms and Threads. So solution by using these two is not acceptable.

You are missing the fact there is a client side/server side disconnect in the web environment.
Your line: ClientScript.RegisterStartupScript (GetType(),"hwa","document.getElementById('fileupload').click();", true); is client side code and will not be executed until the serverside script is comleted and the resulting HTML/javascript/CSS returned to the browser as it is client side javascript. YOu want to be leveraging the onchange event of the file upload control.
The question should help you out: ASP.NET FileUpload: how to automatically post back once a file is selected?

this is not exactly what you are looking for but it does what you want. difference is that instead of clicking a separate button you have to click the Browse button. and when you press the Open button, the page will postback. I have used JQuery for this. here's my code
ASPX
<head runat="server">
<title></title>
<script src="Scripts/jquery-1.9.1.min.js"></script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:FileUpload ID="fileupload1" runat="server" />
<asp:Button ID="btn" runat="server" OnClick="btn_Click" Text="upload" style="display:none" />
</div>
<script type="text/javascript">
var isfirst = true;
$(function () {
$('#<%= fileupload1.ClientID %>').on('change', function (e) {
console.log('change triggered');
$('#<%= btn.ClientID%>').trigger('click'); // trigger the btn button click which i have hidden using style='display:none'
});
});
</script>
</form>
</body>
Code behind
protected void btn_Click(object sender, EventArgs e)
{
//TODO
}

For the ones who land here late,
<div>
<asp:FileUpload ID="fu" runat="server" CssClass="bbbb" onchange="clickSeverControl()"/>
<asp:LinkButton Text="Upload" ID="lnkUpload" runat="server" OnClientClick="showUpload();return false;" OnClick="lnkUpload_Click"/>
</div>
hide the file control with css
<style>
.hiddenStyle {
visibility:hidden;
}
</style>
on client click event of link button trigger the click of file upload control
function showUpload() {
document.getElementById("fu").click();
}
on change event trigger the server side click
function clickSeverControl() {
__doPostBack('<%= lnkUpload.ClientID %>', 'OnClick');
}
on server click save the uploaded file
protected void lnkUpload_Click(object sender, EventArgs e)
{
fu.PostedFile.SaveAs(Server.MapPath("~/Upload") + "/" + fu.PostedFile.FileName);
}

Thanks for the other answer I have just combine two example and got the solution for my problem in my project
<head runat="server">
<title></title>
<script src="Scripts/jquery-1.9.1.min.js"></script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:FileUpload ID="fileupload1" runat="server" />
<asp:Button ID="btnUploadBulk" runat="server" OnClick="btn_Click" Text="upload" style="display:none" />
</div>
<script type="text/javascript">
var isfirst = true;
$(function () {
$('#<%= btnUploadBulk.ClientID%>').on('click', function (e) {
showUpload();
})
});
function showUpload() {
var control = document.getElementById("<%= FileUploadControl.ClientID %>");
control.click();
}
</script>
</form>
Code Behind
protected void btn_Click(object sender, EventArgs e)
{
//TODO
}
This worked for me

How to call a javascript in C# and get a return value?

<script language="javascript" type="text/javascript">
function myjavascriptfn()
{
//debugger;
var strValue= "test";
return strValue
}
How do I call this javascript function in my code behind and proceed appropriately with respective of return values.

You can easily declare JavaScript to be run on the Client using
ScriptManager.RegisterStartupScript(this, this.GetType(), "launchpage", "
function javascriptfn() {
var strValue= 'test';
return strValue;
}
document.getElementById('"+HiddenField1.ClientID+"').value = javascriptfn();
document.getElementById('"+saveProgressButton.ClientID+"').click();
", true);
note: I have divided out the JavaScript out onto multiple lines to make it easier to read but it should all be on one line.
Your problem comes with the second part of the question, sending the data back, you will most likely need a postback (partial or full or handle it with AJAX.
I would add an updatepanel with a asp hiddenfield and a hidden button to trigger it, populate the value of the hidden field with whatever this function is for had have some code in your code behind to capture the event.
<asp:UpdatePanel ID="responcetable" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:HiddenField ID="HiddenField1" runat="server" />
<asp:Button ID="saveProgressButton" runat="server" Text="Button" CssClass="displaynone" />
</ContentTemplate>
<Triggers><asp:AsyncPostBackTrigger ControlID="saveProgressButton" EventName="theeventtodealwiththis" /></Triggers>
</asp:UpdatePanel>
and on the serverside
protected void theeventtodealwiththis(object sender, EventArgs e)
{
// some logic to handle the value returned
}

updating variable from within update panel

im trying to update a variable from within an update panel:
<script type="text/javascript">
var v = 1;
</script>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button ID="btnDone" runat="server" Text="Done" onclick="btnDone_Click" />
<asp:Literal ID="litnew" runat="server"></asp:Literal>
</ContentTemplate>
</asp:UpdatePanel>
<script type="text/javascript">
function updateint() {
alert(v);
}
</script>
<input type="button" onclick="updateint()" />
code behind
protected void btnDone_Click(object sender, EventArgs e)
{
string kiss = LipImageCreator.createImage(); //this returns a file path
litnewlipsurl.Text = "<script> v = '" + kiss + "'; </script>");
}
if i click the button run the updateint() function before i hit the btnDone button i get the alert saying '1' as expected. after i click the btnDone button the javascript is written to the literal as expected but when i click the updateint() button again i still get '1' and not the filepath i was expecting....

You must use ClientScript.RegisterStartupScript() to get the ajax handler to run your script when the postback completes.