Pass extra parameters to an event handler?
C#EventsCallbackC# Problem Overview
Let's say I want to pass some extra data when assigning an event handler. Consider the following code:
private void setup(string someData)
{
Object.assignHandler(evHandler);
}
public void evHandler(Object sender)
{
// need someData here!!!
}
How would I go about getting someData
into my evHandler
method?
C# Solutions
Solution 1 - C#
private void setup(string someData)
{
Object.assignHandler((sender) => evHandler(sender,someData));
}
public void evHandler(Object sender, string someData)
{
// need someData here!!!
}
Solution 2 - C#
I had a hard time figuring out @spender's example above especially with: Object.assignHandler((sender) => evHandler(sender,someData));
because there's no such thing as Object.assignHandler
in the literal sense. So I did a little more Googling and found this example. The answer by Peter Duniho was the one that clicked in my head (this is not my work):
> snip > The usual approach is to use an anonymous method with an event handler > that has your modified signature. For example: > > void Onbutton_click(object sender, EventArgs e, int i) { ... } > > button.Click += delegate(object sender, EventArgs e) > { Onbutton_click(sender, e, 172); }; > > >Of course, you don't have to pass in 172, or even make the third parameter >an int. :)
>/snip
Using that example I was able to pass in two custom ComboBoxItem
objects to a Timer.Elapsed
event using lambda notation:
simulatorTimer.Elapsed +=
(sender, e) => onTimedEvent(sender, e,
(ComboBoxItem) cbPressureSetting.SelectedItem,
(ComboBoxItem) cbTemperatureSetting.SelectedItem);
and then into it's handler:
static void onTimedEvent(object sender, EventArgs e, ComboBoxItem pressure, ComboBoxItem temperature)
{
Console.WriteLine("Requested pressure: {0} PSIA\nRequested temperature: {1}° C", pressure, temperature);
}
This isn't any new code from the examples above, but it does demonstrate how to interpret them. Hopefully someone like me finds it instructive & useful so they don't spend hours trying to understand the concept like I did.
This code works in my project (except for a non-thread-safe exception with the ComboBoxItem
objects that I don't believe changes how the example works). I'm figuring that out now.
Solution 3 - C#
Captured variables:
private void setup(string someData)
{
Object.assignHandler((sender,args) => {
evHandler(sender, someData);
});
}
public void evHandler(Object sender, string someData)
{
// use someData here
}
Or (C# 2.0 alternative):
Object.assignHandler((EventHandler)delegate(object sender,EventArgs args) {
evHandler(sender, someData);
});
Solution 4 - C#
you can try doing this:
string yourObject;
theClassWithTheEvent.myEvent += (sender, model) =>
{
yourObject = "somthing";
}
Solution 5 - C#
My question that was similar was marked a duplicate so thought I'd add an answer here since it won't let me on my question.
class Program
{
delegate void ComponentEventHandler(params dynamic[] args);
event ComponentEventHandler onTest;
static void Main(string[] args)
{
Program prg = new Program();
// can be bound to event and called that way
prg.onTest += prg.Test;
prg.onTest.Invoke("What", 5, 12.0);
Console.ReadKey();
}
public void Test(params dynamic[] values)
{
// assign our params to variables
string name = values[0];
int age = values[1];
double value = values[2];
Console.WriteLine(name);
Console.WriteLine(age);
Console.WriteLine(value);
}
}
Solution 6 - C#
Well, the simplest method id to make someData
a member variable like so:
public class MyClass
{
private string _eventData;
private void setup(string someData)
{
_eventData = someData;
Object.assignHandler(evHandler);
}
public void evHandler()
{
// do something with _eventData here
}
}
I'm not sure that's the best way to do it, but it really depends on the event type, the object, etc.
Solution 7 - C#
You could create a custom object having additional properties based on Object:
class CustomObject : Object
{
public string SomeData;
}
private void setup(string someData)
{
CustomObject customObject = new CustomObject { SomeData = someData };
CustomObject.assignHandler(evHandler);
}
public void evHandler(Object sender)
{
string someData = ((CustomObject)sender).SomeData;
}
If the data should not be changed anymore after initialization, you could also add a custom constructor, for example.
Solution 8 - C#
Here is my one-line solution that pass extra parameters to a timer handler.
private void OnFailed(uint errorCode, string message)
{
ThreadPoolTimer.CreateTimer((timer) => {
UI.ErrorMessage = string.Format("Error: 0x{0:X} {1}", errorCode, message);
}, System.TimeSpan.FromMilliseconds(100));
}