Programmatically set Request["__EVENTTARGET"] from javascript

Question

I'm writing ASP.NET application, and I should check on server-side value of Request["__EVENTTARGET"] in Page_Load. I need to set it value from client-side programmically. I try to set it by this:

document.getElementById('__EVENTTARGET').value = "my_value";

but it doesn't work. Can you help me, why? Thank you!

UPD:

function ShowUploadDialog(obj) {
            document.getElementById('<%= uplReportLogo.ClientID %>').click();
            document.getElementById('<%= hdnInvokeFileUpload.ClientID %>').value = $('input[type=file]').val();
            __doPostBack(obj.id, 'Click');
}

Server controls:

<asp:FileUpload runat="server" ID="uplReportLogo" CssClass="file upload" />
<asp:Button runat="server" ID="btnReportImage" Text="Load Image..." CssClass="button action load" 
     OnClientClick="javascript: return ShowUploadDialog(event, this);" OnClick="btnReportImage_Click" />

UPD2:

function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}

I have "Access denied" exception on row theForm.submit(); Why?

LittleSweetSeas · Accepted Answer · 2013-12-03T17:50:44.730

That variable is used by ASP.NET to store the sender of any postback, so I think your value is getting overwritten each time. You may try to invoke

__doPostBack('my_value','any_other_argument')

by JS, then checking such value in Page_Load event.

For this to work, be sure to remove EventValidation attribute in the first line of your ASPX file.

This is how you can handle it on code-behind:

    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            string _evt = this.Request["__EVENTTARGET"]; // 1st parameter
            string _eva = this.Request["__EVENTARGUMENT"]; // 2nd parameter
            switch (_evt)
            {
                case "my_value":
                    //do anything here
                    break;
                default:
                    break;
            }
        }
    }

EDIT:

Edited to follow your example:

JS:

function ShowUploadDialog() {
        document.getElementById('<%= uplReportLogo.ClientID %>').click();
        document.getElementById('<%= hdnInvokeFileUpload.ClientID %>').value = $('input[type=file]').val();
        __doPostBack('fileUpload', '');
    }

ASPX:

<asp:Button runat="server" ID="btnReportImage" Text="Load Image..." CssClass="button action load" 
        OnClientClick="ShowUploadDialog();"  />

CS:

protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack)
    {
        string _evt = this.Request["__EVENTTARGET"]; // 1st parameter
        string _eva = this.Request["__EVENTARGUMENT"]; // 2nd parameter
        switch (_evt)
        {
            case "fileUpload":
                btnReportImage_Click(); 
                break;
            default:
                break;
        }
    }
}

protected void btnReportImage_Click() // remove sender & event arguments here, you do not need them
{
    //your code
}

yes, I tied it, but when I pass ClientID of my button, I have "Access denied" error — Max Zhukov, Dec 03 '13 at 17:29
I've updated my post and I've added JS function for OnClientClick. But I've also received "Access denied error" — Max Zhukov, Dec 03 '13 at 17:40
No no, you're doing it in a wrong way. Remove OnClick event of your button, use only client-code as my example, and that code will take care of doing the post-back to the server. I edit now — LittleSweetSeas, Dec 03 '13 at 17:46
thanks for your answers. I've updated my post after changing my code with your advices. — Max Zhukov, Dec 03 '13 at 17:51
I need to call FileUpload on client-side and pass value from to server-side by one buttton click — Max Zhukov, Dec 03 '13 at 17:54
This is a security matter of IE. See this: http://stackoverflow.com/questions/13655850/access-denied-error-in-ie-when-submitting-form-through-javascript — LittleSweetSeas, Dec 04 '13 at 13:35

score 0 · Answer 2 · answered Sep 30 '15 at 05:16

it's due to the access denied error the form is unable to submit, You just need to override the function generated by framework and handle the exception untill the form is not submitted just keep calling this function. I got the same problem and it is resolved now. Add this function on your page. B.O.Luck

function __doPostBack(eventTarget, eventArgument) {
        try {
            if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
                theForm.__EVENTTARGET.value = eventTarget;
                theForm.__EVENTARGUMENT.value = eventArgument;
                theForm.submit();

            }
        }
        catch (e) {

            __doPostBack(eventTarget, eventArgument);
        }

    }

Programmatically set Request["__EVENTTARGET"] from javascript

2 Answers2