How to raise the SelectedIndexChanged event of an asp.net List control in a codebehind using C#?
If you're asking how to manually fire the event so that it can run whatever logic is attached: don't.
Your event handlers should be slim. If you need to perform the same operation from multiple places, then extract that functionality into its own method and have the event handler invoke that. For example:
private void CountryListBox_SelectedIndexChanged(object sender, EventArgs e)
{
UpdateStates(ListBox1.SelectedItem.Text);
}
private void UpdateStates(string country)
{
StateListBox.DataSource = GetStates(country);
StateListBox.DataBind();
}
Now instead of trying to fire the SelectedIndexChanged event, you just invoke the method that this event handler refers to, i.e.
private void Page_Load(object sender, EventArgs e)
{
UpdateStates("USA");
}
Don't put complex logic in event handlers and try to raise those events from unexpected places. Instead, put the complex logic in its own method, so that you can perform the associated actions from elsewhere.
It is raised automatically.
Go in the Events section, lightening
bolt in properties window
alt text http://img704.imageshack.us/img704/6100/listbox.jpg
double click the place holder next to
event. This is what you will get.
protected void ListBox1_SelectedIndexChanged(object
sender, EventArgs e)
{
}
if you want to raise this event from another code block then, call
ListBox1_SelectedIndexChanged(sender,
e);
If what you want is more than just executing the code behaviour coded for the selected index (like listed in the previous answer), the short answer is there is no easy way. You can write a simple code that on prerender or render to explicitly define the control id variable in your rendered HTML and then use javascript to set the selected index. This will cause the postback that trigger the event. Alternatively you can register an ajax call back method and have the client calls that either when some event happened or by automatic timer.
Related
I want to run code in a button event handler but the if(Page.IsPostBack) conditional is running first and contains a redirect so the event never runs.
protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack)
{
(do some stuff with save button pressed...)
// then return the same page to prevent another post on refresh
Response.Redirect(Request.Url.AbsoluteUri);
}
}
and on that page there is another button that calls a handler:
protected void Export_Click(object sender, EventArgs e)
{
(do other stuff..)
}
Is there a way to run the handler first or a way to check which button was clicked so I can add a conditional to the redirect?
Thanks.
This behavior is actually by design in WebForms. To keep things stateless, a full postback occurs whenever you wish to fire off a server-side event.
So the short answer is no, you cannot force your event to occur before the Page_Load does.
However, you can restructure your design a bit to get the behavior you desire. At the moment, it looks as though you are depending on a PostBack having a occurred to execute your save logic. Instead of handling the logic in your Page_Load event, it could be handled in an event appropriate to how your user is expecting to save.
If saving is triggered through a button press, then moving logic for handling the save and redirect to a Save_Click event will allow other events related to PostBack to execute their own logic as well.
I need help on firing an event within C#
Basically I have a onclick event that fires when you click on a checkbox
void OnClick(object sender, RoutedEventArgs e)
{
...
}
I need help on firing an event within C#
Basically I have a onclick event that fires when you click on a checkbox
void OnClick(object sender, RoutedEventArgs e)
{
...
}
However, I need to fire this event once another event has been fired, so within this new event, is it possible I can fire the above one?
private void DataGridCell_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
switch(dataGrid.Name)
{
case "Customer"
//fire OnCLick Event
break;
}
}
I have tried something like
??? += new MouseEventHandler(OnClick);
But I am not sure if this will actually work.
Yes you can, but only if the event is in your own class. You can't even raise a base class' event. You have a put a method in the base class to raise the event, and then call that.
The code you put there is adding another event handler, not raising an event; you don't need to do that.
If it's a button, use btnDoSomething.PerformClickEvent (winforms)
If the handler is in your code, you can call it without raising the event (commenters assume that this is what you want to do but in reaslity there are many cases where you'd need more than this) btnDoSomething_Click(null, null) - null usually works because handler code rarely cares about the sender or arguments and if you don't reference them, you don't need them.
If you can use #4, you can also refactor as mentioned. Usually not needed. But usually so easy to do you it's worth doing for clarity anyway.
For objects that map from Windows widgets of anysort, check out the SendMessage and PostMessage API calls. Wayyyy beyond the scope of this answer, though. Doesn't apply to non-windows-backed objects (but your sample implies windows).
Hello
I have read that events can be raised the same way as methods. Well it works for my custom events (I create a delegate, the event and I am able to raise the event by calling it).
However I am not able to manually raise events like MouseClick and other, it keeps saying that it must appear on the left side of the += operator. What is the problem?
While I am certain you'll get other answers more informative than this one, basically you can't "raise" an event outside the class that contains it. MSDN has this to say about events
Events are a special kind of multicast
delegate that can only be invoked from
within the class or struct where they
are declared (the publisher class). If
other classes or structs subscribe to
the event, their event handler methods
will be called when the publisher
class raises the event.
If you wanted to literally raise the event for, say, a Windows Forms Control MouseClick, you'd have to create a subclass of that control and either invoke base.OnMouseClick() or override it.
If this is a button, you can programmatically click it using the PerformClick method.
Sadly, this only works on buttons and not other types of Controls... except MenuItem.
If you want to click button you should call:
button1.PerformClick();
If you want to call MouseClick please refer to this forum, there is solution in c# using windows api:
private void button1_Click(object sender, EventArgs e)
{
//Enter your code here
}
void Page_Load(object sender, EventArgs e){
this.button1.Click += new System.EventHandler(this.button1_Click);
this.button1_Click(this, e);
}
Let's say you want to manually raise the event "click". This works for me:
public partial class CustomButton : UserControl
{
public new event EventHandler Click;
private void lblText_Click(object sender, EventArgs e)
{
Click(this, e);
}
}
I have built an ascx control that is part of many different components of my application. There is a Previous and Next button on this control, which should be signaled to the parent aspx page. This is done by having the parent page add some Delegates for postbacks, such as OnPreviousClicked, OnNextClicked etc.
Everything in this app is 'ajaxified' with an updatepanel. Now I notice that my app breaks if I don't set the delegates on every single Page_Load call in the parent. In other words, if I don't ALWAYS set the delegates in the Page_Load of the parent aspx, then the ascx ends up with null delegates and an exception. Am I coding stuff correctly?
// inside the control
public event EventHandler OnPreviousClicked;
private void PreviousButton_OnClick(object sender, EventArgs e)
{
if(OnPreviousClicked != null) {
OnPreviousClicked(this, e); // or whatever args you want
}
}
// and inside the Page code-behind
private void Page_Load(...)
{
MyUserControl.OnPreviousClicked += new EventHandler(myHandler);
}
// OR inside the Page aspx, you also could just set the OnPreviousClicked property.
<xx:MyUserControl ID="MyUserControl1" runat="server" OnPreviousClicked="myHandler" />
See http://asp.net-tutorials.com/user-controls/events/.
If all you're doing is signaling the clicking of a button, I would have your ASCX control raise a simple event instead. That way each page can listen for the event if they need to and the controls can function regardless if anybody is listening.
First declare the events in your ASCX codebehind:
public event System.EventHandler NextSelected;
Then you create your button click events that raise the event.
protected void btnNextSelected_Click(object sender, EventArgs e)
{
if (EmployeeSelected != null)
{
NextSelected(this, new EventArgs());
}
}
Then in your parent ASP.Net pages you can add your ASCX control (we'll call it NavControl) and create methods that listen for these events.
NavControl.NextSelected += new EventHandler(NextPageRedirect);
protected void NextPageRedirect(object sender, EventArgs e)
{
Response.Redirect("~/ViewEmployee.aspx", false);
}
Note that with this you don't have to create the event handler or method and you can still use the nav control on your page. It should also eliminate the issues you are having with the delegates.
remember each postback has to restart your code. The event handlers don't get serialized to viewstate so you have to set them up again.
That is the expected behavior in asp.net.
The entire page life cycle occurs even when it is a partial postback (update panel). So in order for the events to fire, you will have to wire them up programmatically during page_load or declaratively in your markup (if those delegates you mentioned are events).
Say I have a composite control in ASP.NET (C#) which includes a drop down list. I need to be able to bubble the event back to the parent form so that other code can be executed based on its SelectedItem.
How do I expose the OnSelectedItemChanged event to the application?
Do I need to create my own delegate and raise it when the internal drop down list item is changed?
I've created control which contains a button and I'm using same approach; create a delegate and raise events on button's click.
public delegate void IndexChangeEventHandler(object sender, EventArgs e);
public event IndexChangeEventHandler SelectedIndexChanged = delegate { };
//this is in your composite control, handling ddl's index change event
protected void DDL_SelectedIndexchanged(object sender, EventArgs e)
{
SelectedIndexChanged(this, e);
}
Correct... You would want to create your own event for SelectedItem and write an event handler for the dropdown list's SelectedItem and inside the method raise your event.