This question already has answers here:
RoutedEventArgs.Source vs Sender
(4 answers)
How do C# Events work behind the scenes?
(2 answers)
Closed 5 years ago.
I don't understand what event parameters do in C#. Let's say we have a button called CoffeeButton, and clicking on it takes you to another Page called Coffee using a Frame called myFrame.
This is my code:
private void CoffeButton_Click(object sender, RoutedEventArgs e)
{
MyFrame.Navigate(typeof(Coffee));
}
What does object sender and RoutedEventArgs e do in this case?
Examples would be great!
Normally, "sender" will be a reference to whatever object fired the event. So if, for example, you have more than one Button that all wire into the same button_Click handler function, the sender object would be a reference to whichever actual Button object was clicked.
The EventArgs object that's normally passed in as the second parameter is used for different things depending on the context. Generally, it's used to pass you additional information related to the event that happened. For example, in this case, the RouteEventArgs object provides a RoutedEvent property that you can look at if you need to.
Related
What do sender and eventArgs mean/refer to? How can I make use of them (for the scenario below)?
Scenario:
I'm trying to build a custom control with a delete function, and I want to be able to delete the control that was clicked on a page that contains many of the same custom control.
The sender is the control that the action is for (say OnClick, it's the button).
The EventArgs are arguments that the implementor of this event may find useful. With OnClick it contains nothing good, but in some events, like say in a GridView 'SelectedIndexChanged', it will contain the new index, or some other useful data.
What Chris is saying is you can do this:
protected void someButton_Click (object sender, EventArgs ea)
{
Button someButton = sender as Button;
if(someButton != null)
{
someButton.Text = "I was clicked!";
}
}
sender refers to the object that invoked the event that fired the event handler. This is useful if you have many objects using the same event handler.
EventArgs is something of a dummy base class. In and of itself it's more or less useless, but if you derive from it, you can add whatever data you need to pass to your event handlers.
When you implement your own events, use an EventHandler or EventHandler<T> as their type. This guarantees that you'll have exactly these two parameters for all your events (which is a good thing).
Manually cast the sender to the type of your custom control, and then use it to delete or disable etc. Eg, something like this:
private void myCustomControl_Click(object sender, EventArgs e)
{
((MyCustomControl)sender).DoWhatever();
}
The 'sender' is just the object that was actioned (eg clicked).
The event args is subclassed for more complex controls, eg a treeview, so that you can know more details about the event, eg exactly where they clicked.
'sender' is called object which has some action perform on some
control
'event' its having some information about control which has
some behavoiur and identity perform
by some user.when action will
generate by occuring for event add
it keep within array is called event
agrs
FYI, sender and e are not specific to ASP.NET or to C#. See Events (C# Programming Guide) and Events in Visual Basic.
This question already has answers here:
Pass extra parameters to an event handler?
(10 answers)
Closed 6 years ago.
I have the following:
private void ButtonClick(object sender, EventArgs e)
When I add to the parameter list, to make:
private void ButtonClick(object sender, EventArgs e, Class c)
then it will cause all sorts of problems. However, I need really want in my main:
Class c = new Class();
And then I would like to click a button so that ButtonClick is called, but I really need access to the "Class c" in the function body, so I really need
private void ButtonClick(object sender, EventArgs e, Class c)
to compile somehow.
I have tried other ways around the issue, such as making Class static, but it would create too much refactoring and cause other errors.
I don't know if this will be possible in Windows Forms. I am not opposed to switching over to XAML and WPF, I just want to know that doing something such as
private void ButtontClick(object sender, EventArgs e, Class c)
will be possible.
Just make your Class c variable a member variable in your main class where your ButtonClick event handler is located. Unless this ButtonClick event handler is your own custom event handler, you can't add more parameters to the framework's Click event handler for a button. You will have to access your Class c variable as a member variable or use commands and command bindings with command parameters.
You can put c in the Button.Tag property and use ((Button)sender).Tag in the click event handler to get it.
This question already has answers here:
C# Windows Forms code not working - Attach Event to button
(2 answers)
Forms not responding to KeyDown events
(3 answers)
Closed 7 years ago.
It is my second day doing c#...don't judge please. I have read other threads but they did not help.
I have this code:
private void listView1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Delete)
{
MessageBox.Show("aa");
}
}
which is not working.
What am I doing wrong?
The issue is that you haven't told the ListView to actually use the event. To do this you have to assign the method to the required event. there are two ways to do this. Either select the ListView and open the Properties tab go to events and double click on the one you want. (Visual studio will automatically put the event out for you). Or in the constructor of the form or elsewhere you can manually assign it. In your case it would look like...
listView1.KeyDown += listView1_KeyDown;
Note you don't have to use a name similar to what visual studio would automatically produce. You can name your method whatever you want as long as the method signature matches the event. This is nice if you have multiple list boxes and want to use the same method to handle all of them. For example you could do something like.
listView2.KeyDown += listView1_KeyDown;
I suggest reading up on how events work in c#.
What I'm trying to do here is really simple but it's not working for me. I've looked up many examples of very similar or matching questions on stackoverflow and others and their solutions haven't worked for me.
Basically (in a very simplified form), I have a button with some text in it. I'd like it so when this button is clicked, a message box shows up displaying the text. However, I have 9 of these buttons (think numbers on a calculator), and I'd like to create a single method that handles all of these clicks, and outputs the correct text depending on the button.. which is why I need to pass the button as a parameter.
Here's the code I have for the method that handles it so far:
private void btn_Click(object sender, EventArgs e, Button b)
{
MessageBox.Show(b.Text);
}
The above small code snippet is the same solution that others have used and had working. However, for me this code doesn't compile and shows an error that says No overload for 'btn_Click' matches delegate 'System.EventHandler'.
When I double click on that error, it takes me to the Designer.cs page for the form, and this is the line of code that has the error:
this.btnN7.Click += new System.EventHandler(this.btnN7_Click);
I have no clue what the overload and delegate parts mean, sorry I'm pretty new to this. I was thinking that maybe overload has to do with constructors but even if that's correct, I'm unsure of what the next step would be.
I have System.Windows.Forms; included properly so the issue shouldn't be that the Button object wasn't recognized.
If you could provide any insight as to what I'm missing or doing wrong, that'd be very sweet! Please let me know if you need any additional information to continue.
And lastly, this is unrelated to my issue but it's a small question that's been irking me ever since I started using VS a week ago: Are the control parameters object sender and EventArgs e that are automatically created for controller events even necessary? Most of the examples I've looked up online omit them. I've just kept them in since they were created by default but I don't really know what kind of function they provide, and I've never had to use those parameters in my methods.
Thanks all! =)
You just need to use sender parameter.You can't subscribe an event handler if the method signature doesn't match with the EventHandler delegate.
private void btn_Click(object sender, EventArgs e)
{
var currentButton = sender as Button;
if(currentButton != null) MessageBox.Show(currentButton.Text);
}
sender will be assigned to an object that triggers the event.So for instance when your button2 is clicked, it will be assigned to button2.Ofcourse you need to attach this event handler to button2's Click event.I have also used the as operator to ensure that a button is triggered the event.In the future if you call this method manually like btn_Click(this, EventArgs.Empty) then the explicit cast will throw an InvalidCastException.Using as operator is always better to avoid this.If the type of the sender is different than Button then currentButton will be null.
which is why I need to pass the button as a parameter.
You don't really have to create that extra parameter. What you need is already there.
object sender is a source of the event, so just call
var btn = (Button) sender;
MessageBox.Show(btn.Text);
and you should be fine.
Are the control parameters object sender and EventArgs e that are automatically created for controller events even necessary?
So now you have a part of an answer for this question. The second part (EventArgs) are needed for passing additional information. Read more about event args on MSDN.
You have two options here:
If you want to access to the button that fired the event, you can do it trough sender
private void btn_Click(object sender, EventArgs e)
{
Button b = (Button)sender;
MessageBox.Show(b.Text);
}
Otherwise, access directly through the button name (in case you know it)
This question already has an answer here:
Is there any event that fires when WPF animation ends?
(1 answer)
Closed 9 years ago.
Is there a possibility to register a function to a Animated Usercontroll that is called when the animation is over?
I have a Usercontroll-Animation I start by calling .BeginAnimation(propdp, animation);
How to call another function when the Animation is over?
There is a Timeline.Completed Event that you can use. You can either set it in XAML, or in C# on a Storyboard instance. The linked page has a full working example that you can view.
The handler used is the default EventHandler delegate:
private void StoryboardCompleted(object sender, EventArgs e)
{
// the Storyboard has stopped
}
UPDATE >>>
Although the Completed event can be set on a Storyboard instance, it is in fact defined in the Timeline class. As Timeline is the base class for all AnimationTimeline classes, this means that you can also attach a handler to the Completed event from the AnimationTimeline object that you are passing into the BeginAnimation event.
There is an animation.Completed event.