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Add Event Handler On Button At Run Time In ASP.NET

Consider a scenario in which you have been given a task to create 2 screens, one is Registration Screen and other is Manage Profile screen. Both the screens contain the same fields.

The only difference is when Registration Screen is loaded then all the fields are empty and while in Manage Profile screen, the contents are preloaded from the database. So, you have decided to create a single web form and add or update the content depends upon the value in the query string.

There is a button "btnSave" in which you write logic of both the operations i.e. add and update. You may write a code like

protected void btnSave_Click(object sender, EventArgs e) { 
    if (Request.QueryString.Keys.Count > 0) { 
        //   Write a logic for update 
    } 
    else { 
        //   Write a logic for add 
    } 
}

This approach is fine as long as the logic is small, but if your logic contains so many lines of code then it will be very difficult for you to manage the code in the future.

There may be many approaches to deal with this situation. One approach is to create two different function one contains the logic for add and other contains the logic for update. The approach is fine. But this approach makes the button click event strongly coupled. Wouldn’t it be nice if you can make the event loosely coupled.

In this tutorial, I will explain how to implement the scenario in a better way by adding an event handler to button click event at run time.

Implementation

First of all create a website and add a button in Default.aspx page.

<body>
	<form id="form1" runat="server">
		<div>
			<asp:Button ID="btnSave" runat="server" Text="Save" />
		</div>
	</form>
</body>

In the above code, I have not added the "OnClick" attribute. The click event will be added at runtime. In the code behind part first of all create 2 event handlers

public EventHandler addButtonClickEventHandler; 
public EventHandler updateButtonClickEventHandler;

The first event handler i.e. addButtonClickEventHandler handles the add logic and second event handler i.e. updateButtonClickEventHandler handles the update logic.

On the page load event, add the below code

addButtonClickEventHandler = new EventHandler(addEvent); 
updateButtonClickEventHandler = new EventHandler(updateEvent); 
  
if (Request.QueryString.Keys.Count > 0) { 
    btnSave.Click -= addButtonClickEventHandler; 
    btnSave.Click += updateButtonClickEventHandler; 
} 
else { 
    btnSave.Click -= updateButtonClickEventHandler; 
    btnSave.Click += addButtonClickEventHandler; 
}

In the first two lines of code, I am initializing event handler variables. In the next lines, I am checking whether there is any query string appended in the URL of the webpage. If yes then it means the web page is in the update mode, so update event handler is added in the button click event and add event handler is removed and vice versa.

Check the Initialization part again. In the input parameter of EventHandler constructor, we have passed addEvent and updateEvent. These are the two methods which handles the add and update logic.

void addEvent(object sender, EventArgs e) { 
    //   Write an add logic 
} 
void updateEvent(object sender, EventArgs e) { 
    //   Write an update logic 
}

See the signature of the methods. Both methods has the same signature as of "btnSave_Click" method. The implementation part is done.

As per my opinion this approach is better than adding an if else logic on button click as this approach makes the system loosely coupled.

Posted By -	Karan Gupta

Posted On -	Monday, December 26, 2011

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