Problems with asp:Button OnClick event

Question

Here is my button

<asp:Button ID="myButton" Text="Click Me" OnClick="doSomething(10)" runat="server" />

Here is the server function

public void doSomething(int num)
{
    int someOtherNum = 10 + num;
}

When I try to compile the code I get the error "Method Name Expected" for the line:

<asp:Button ID="myButton" Text="Click Me" OnClick="doSomething(10)" runat="server" />

What am I doing wrong? Am I not allowed to pass values to the server from an OnClick event?

Solution 1

There are two problems here. First, the onclick event has a specific signature. It is

MethodName(object sender, EventArgs e);

Second, in the markup, you need to pass the Method name only with no parentheses or params.

<asp:Button ID="myButton" Text="Click Me" OnClick="doSomething" runat="server" />

Then change your codebehind as follows:

public void doSomething(object sender, EventArgs e)
{
    ....
}

The passing of parameters can done on a client side click event handler, in this case OnClientClick, but not on the server side handler.

Solution 2

There is simpler solution. You could use ASP button OnCommand event. More about here: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.button.oncommand.aspx

Solution 3

OnClick of the Button is an Event Handler. To hook a function to an eventHandler you need to obey the Contract that was defined by the EventHandler, as mentioned by Jose. OnClick is bound to a function of the format void doSomething(object sender, EventArgs e). So your function should be of the same format.

I am unsure why would want to pass a parameter to the Event Handler. If you want to take some manuplation you need to do that using some other control.

<asp:TextBox ID="txtNumber" runat="server" /><asp:Button ID="myButton" Text="Click Me" OnClick="doSomething" runat="server" />

And in the Code

public void doSomething(object sender, EventArgs e)
{
int AnotherNumber=   Int32.Parse(txtNumber.Text)+10;
}

Comments

[Matt]

So there's absolutely no way to pass that method a number as long as it's a server side method?

[Jose Basilio]

That's correct. You can however, read values from other input fields like textboxes or even hidden controls from inside your event handler and use that for your input calculations.