The BackgroundWorker object allows us to pass a single argument into the DoWorkEventHandler.
// setup/init:
BackgroundWorker endCallWorker = new BackgroundWorker();
endCallWorker.DoWork += new DoWorkEventHandler(EndCallWorker_DoWork);
...
endCallWorker.RunWorkerAsync(userName);
// the handler:
private void EndCallWorker_DoWork(object sender, DoWorkEventArgs e)
{
string userName = e.Argument as string;
...
}
To pass multiple arguments, I must wrap them in an object, like this poor string array:
// setup/init:
BackgroundWorker startCallWorker = new BackgroundWorker();
startCallWorker.DoWork += new DoWorkEventHandler(StartCallWorker_DoWork);
...
startCallWorker.RunWorkerAsync(new string[]{userName, targetNumber});
// the handler:
private void StartCallWorker_DoWork(object sender, DoWorkEventArgs e)
{
string[] args = e.Argument as string[];
string userName = args[0];
string targetNumber = args[1];
}
Is there another object or pattern that allows us pass multiple arguments nicely, or ideally, write our own signature?
You could use a closure (Lambda):
backgroundWorker.DoWork += (s, e) => MyWorkMethod(userName, targetNumber);
Or with delegate (anonymous method) syntax:
backgroundWorker.DoWork +=
delegate(object sender, DoWorkEventArgs e)
{
MyWorkMethod(userName, targetNumber);
};
What's wrong with using a typed object?
internal class UserArgs
{
internal string UserName { get; set; }
internal string TargetNumber { get; set; }
}
var args = new UserArgs() {UserName="Me", TargetNumber="123" };
startCallWorker.RunWorkerAsync(args);
instead of a typed object. C# 4.0 provides us with tuple. We could use a tuple to hold multiple args. Then there is no need to declare a new class.
Object can be a list or array or some such. Just make your object a container of some sort, then cast within the BackgroundWorker. You need to make sure you're always passing in the same type though.
Maybe pass a lambda function as your object? Then you'd call it in the DoWork handler.
endCallWorker.RunWorkerAsync(new Action( () => DelegatedCallTarget(userName, targetNumber) ));
Create a class that holds all your arguments
Class MyClass
{
private string m_Username = string.Empty;
private int m_Targetnumber;
public MyClass(){}
public string Username
{
get { return m_Username; }
set { m_Username = value; }
}
public int TargetNumber
{
get { return m_TargetNumber; }
set { m_TargetNumber = value; }
}
}
// setup/init:
BackgroundWorker startCallWorker = new BackgroundWorker();
startCallWorker.DoWork += new DoWorkEventHandler(StartCallWorker_DoWork);
...
MyClass thisClass = new MyClass();
thisClass.Username = "abcd";
thisClass.TargetNumber = 1234;
startCallWorker.RunWorkerAsync(thisClass);
// the handler:
private void StartCallWorker_DoWork(object sender, DoWorkEventArgs e)
{
MyClass args = (MyClass)e.Argument;
string userName = args.Username;
string targetNumber = args.TargetNumber;
}
Why not have the "one" object passed be an array of parameters? You only need to cast it back to array inside the method from the object parameter.
Related
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?
private void setup(string someData)
{
Object.assignHandler((sender) => evHandler(sender,someData));
}
public void evHandler(Object sender, string someData)
{
// need someData here!!!
}
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.
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);
});
you can try doing this:
string yourObject;
theClassWithTheEvent.myEvent += (sender, model) =>
{
yourObject = "somthing";
}
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);
}
}
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.
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.
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));
}
This solution offers a way to pass extra parameters to an event handler while still allowing to unsubscibe:
Within the Subscribe() function of my example I create an Action that invokes a lambda function that supplies my event handler with the event args and my extra parameter. I then store this Action in a dictionary. When I want to unsubscribe, I can use the stored Actions to do so.
This works, I read the length of listeners before and after unsubscribing and it did decrease - you can unsubscribe again without problems.
public class Player
{
public Action<JumpInfo> OnJump;
}
public class PlayerJumpListener
{
public List<Player> MyPlayerList;
private Dictionary<Player, Action<JumpInfo>> _jumpActionsByPlayer = new Dictionary<Player, Action<JumpInfo>>();
private void Subscribe()
{
foreach (Player player in MyPlayerList)
{
Action<JumpInfo> playerJumpAction = (jumpInfo) => HandlePlayerJump(jumpInfo, player);
player.OnJump += playerJumpAction;
_jumpActionsByPlayer.Add(player, playerJumpAction);
}
}
private void Unsubscibe()
{
foreach (KeyValuePair<Player, Action<JumpInfo>> kvp in _jumpActionsByPlayer)
{
kvp.Key.OnJump -= kvp.Value;
}
}
private void HandlePlayerJump(JumpInfo jumpInfo, Player player)
{
// player jumped
}
}
I scoured the internet before a coworker kindly helped me, and boy I felt dumb. Brackets is the solution for the EventHandler.
Ex.
event EventHandler<(int, bool)> EventName;
and then pick it up with:
private void Delegate_EventName(object sender, (int, bool) e)
you can then access the info:
var temp = e.Item1;<br>
var temp2 = e.Item2;<br>
or you can add names as you would expect for parameters and call them via e:
private void Delegate_EventName(object sender, (int num, bool val) e)
you can then access the info:
var temp = e.num;
var temp2 = e.val;
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?
private void setup(string someData)
{
Object.assignHandler((sender) => evHandler(sender,someData));
}
public void evHandler(Object sender, string someData)
{
// need someData here!!!
}
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.
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);
});
you can try doing this:
string yourObject;
theClassWithTheEvent.myEvent += (sender, model) =>
{
yourObject = "somthing";
}
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);
}
}
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.
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.
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));
}
This solution offers a way to pass extra parameters to an event handler while still allowing to unsubscibe:
Within the Subscribe() function of my example I create an Action that invokes a lambda function that supplies my event handler with the event args and my extra parameter. I then store this Action in a dictionary. When I want to unsubscribe, I can use the stored Actions to do so.
This works, I read the length of listeners before and after unsubscribing and it did decrease - you can unsubscribe again without problems.
public class Player
{
public Action<JumpInfo> OnJump;
}
public class PlayerJumpListener
{
public List<Player> MyPlayerList;
private Dictionary<Player, Action<JumpInfo>> _jumpActionsByPlayer = new Dictionary<Player, Action<JumpInfo>>();
private void Subscribe()
{
foreach (Player player in MyPlayerList)
{
Action<JumpInfo> playerJumpAction = (jumpInfo) => HandlePlayerJump(jumpInfo, player);
player.OnJump += playerJumpAction;
_jumpActionsByPlayer.Add(player, playerJumpAction);
}
}
private void Unsubscibe()
{
foreach (KeyValuePair<Player, Action<JumpInfo>> kvp in _jumpActionsByPlayer)
{
kvp.Key.OnJump -= kvp.Value;
}
}
private void HandlePlayerJump(JumpInfo jumpInfo, Player player)
{
// player jumped
}
}
I scoured the internet before a coworker kindly helped me, and boy I felt dumb. Brackets is the solution for the EventHandler.
Ex.
event EventHandler<(int, bool)> EventName;
and then pick it up with:
private void Delegate_EventName(object sender, (int, bool) e)
you can then access the info:
var temp = e.Item1;<br>
var temp2 = e.Item2;<br>
or you can add names as you would expect for parameters and call them via e:
private void Delegate_EventName(object sender, (int num, bool val) e)
you can then access the info:
var temp = e.num;
var temp2 = e.val;
I want to get my field >>> NumberOfElementsInMyList from sender, How Can I do it? I couldn't find this kind of question here (what I have seen, was about windows forms), so ...
class Program
{
static void Main(string[] args)
{
Publisher PublisherObject = new Publisher();
PublisherObject.NumberAdded += PublisherObject_NumberAdded;
PublisherObject.AddNumber(int.Parse(Console.ReadLine());
}
static void PublisherObject_NumberAdded(object sender, EventArgs e)
{
//I want to write on the console "NumberOfElementsInMylist"
//I tried:
//sender.NumberOfElementsInMylist -- not works
//Publisher obj=(publisher)sender and then sender.NumberOfElementsInMylist
//not works
Console.WriteLine("number of elements in list is ---> "+ ???? );
}
}
class Publisher
{
public event EventHandler NumberAdded;
public int NumberOfElementsInMyList;
List<int> MyList=new List<int>();
public void AddNumber(int NumberToAdd)
{
MyList.Add(NumberToAdd);
NumberOfElementsInMyList = MyList.Count;
NumberAdded(this, new EventArgs());
}
}
To literally answer your question, the reason why you can't access the NumberOfElementsInMyList field is because when you create the EventArgs, your instance of Publisher is being cast as an object (which you can do since all classes inherit from object.) So to see the properties (or field) of Publisher, you have to cast the sender as Publisher.
var numberOfElements = ((Publisher)sender).NumberOfElementsInMyList;
A downside to this is that hypothetically, sender might not be a Publisher. Because sender is an object, it could technically be anything.
You can also create your own event handler delegate and event args instead of using the boilerplate EventHandler delegate.
public delegate void NumberAdded(Publisher source, NumberAddedEventArgs eventArgs);
public class NumberAddedEventArgs : EventArgs
{
public NumberAddedEventArgs(int numberAdded, numberOfItemsInList)
{
NumberAdded = numberAdded;
NumberOfItemsInList = numberOfItemsInList;
}
public int NumberAdded { get; private set; }
public int NumberOfItemsInList { get; private set; }
}
public class Publisher
{
public event EventHandler NumberAddedEvent;
public int NumberOfElementsInMyList;
List<int> MyList = new List<int>();
public void AddNumber(int NumberToAdd)
{
MyList.Add(NumberToAdd);
NumberOfElementsInMyList = MyList.Count;
NumberAddedEvent?.Invoke(this, new NumberAddedEventArgs(NumberToAdd,
NumberOfElementsInMyList));
}
}
var numberOfElementsInList = args.NumberOfItemsInList; // much better!
The (object sender, EventArgs args) is a strange convention. In any other scenario we would create strongly-typed methods and delegates. But in this case there's a tendency to use something that's not strongly-typed because it's a convention.
You can simply cast the sender, can't you?
var publisher = (Publisher)sender;
Console.WriteLine(publisher.NumberOfElementsInMyList);
Or more safely:
Console.WriteLine(
(sender as Publisher)?.NumberOfElementsInMyList?.ToString() ?? "sender is not a publisher!");
I'm trying to programmatically call a function with event.
How to convert string to a event in general? My problem is actually not knowing How to do this?
How to convert str to event?
str = "test1";
// UserControlsBackgroundEventArgs = EventArgs
EventArgs arg = (EventArgs)str; --> ?
UserControlsBackgroundOutput(str);
//function
private string CLICKNAME = "test0";
private void UserControlsBackgroundOutput(EventArgs e)
{
if (CLICKNAME == e.output)
return;
if (e.output == "test1"){}
}
Error solved:
I had to do
UserControlsBackgroundEventArgs arg = new UserControlsBackgroundEventArgs(CLICKNAME);
instead of
UserControlsBackgroundEventArgs arg = new (UserControlsBackgroundEventArgs)(CLICKNAME);
i've written a code that mimic you code, hopefully you will find it useful:
public class UserControlsBackgroundEventArgs
{
public string output;
public UserControlsBackgroundEventArgs(string up)
{
output = up;
}
}
public delegate void UserControlsBackgroundOutputHandle(UserControlsBackgroundEventArgs e);
public class testEvent
{
public event UserControlsBackgroundOutputHandle UserControlsBackgroundOutput;
public void DoSomeThings()
{
// do some things
if (UserControlsBackgroundOutput != null)
{
string str = "test1";
UserControlsBackgroundEventArgs arg = new UserControlsBackgroundEventArgs(str);
UserControlsBackgroundOutput(arg); // you've done that with str, whitch makes me
// you don't know what the event param is
}
}
}
public class test
{
private testEvent myTest;
private const string CLICKNAME = "whatever"; // i don't know what you want here
public test()
{
myTest = new testEvent();
myTest.UserControlsBackgroundOutput += UserControlsBackgroundOutput;
}
void UserControlsBackgroundOutput(UserControlsBackgroundEventArgs e)
{
if (CLICKNAME == e.output)
return;
if (e.output == "test1")
{
}
}
}
Your event class needs to have a constructor accepting a string. Then you will be able to create a new event instance using a string. You can't "convert" a string to an instance of the event class. If the event class comes from a library or sth and doesn't have a string constructor, you can subclass it, implement a string constructor and override the output property.
If you want this kind of conversion to be possible, you have to use an explicit operator:
public static explicit operator UserControlsBackgroundEventArgs(string s)
{
var args = new UserControlsBackgroundEventArgs();
args.output = s;
return args;
}
This is only possible with a new class, not with EventArgs, because you can't change the code of that class.
Your UserControlsBackgroundEventArgs Implementation could provide implicit/explicit casts.
Take a look at implicit keyword documentation
However, the answer from Wojciech Budniak is better.
Visual Studio 2008, C# 3.0.
I have a method below which calls an event handler. I would like to pass the two arguments received by the method to the event handler.
I would like to do something like this:
wc.DownloadDataCompleted += wc.DownloadedDataCompleted(strtitle, placeid);
Is this even possible, if yes, how would I go about doing it ?
Code Snippet:
public void downloadphoto(string struri,string strtitle,string placeid)
{
using (WebClient wc = new WebClient())
{
wc.DownloadDataCompleted += wc_DownloadDataCompleted;
wc.DownloadDataAsync(new Uri(struri));
}
}
The easiest way to do this is to use an anonymous function (an anonymous method or a lambda expression) to subscribe to the event, then make your method have just the parameters you want:
public void downloadphoto(string struri, string strtitle, string placeid)
{
using (WebClient wc = new WebClient())
{
wc.DownloadDataCompleted += (sender, args) =>
DownloadDataCompleted(strtitle, placeid, args);
wc.DownloadDataAsync(new Uri(struri));
}
}
// Please rename the method to say what it does rather than where it's used :)
private void DownloadDataCompleted(string title, string id,
DownloadDataCompletedEventArgs args)
{
// Do stuff here
}
DownloadDataAsync has an overload which takes an object:
DownloadDataAsync(uri, object)
That object can be any arbitrary thing you want that gets passed into the DownloadDataCompleted handler:
public void downloadphoto(string struri,string strtitle,string placeid)
{
using (WebClient wc = new WebClient())
{
string[] data = new string[2] { strtitle, placeid };
wc.DownloadDataCompleted += wc_DownloadDataCompleted;
wc.DownloadDataAsync(new Uri(struri), data);
}
}
void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
string[] data = (string[])e.UserToken;
string strtitle = data[0];
string placeid = data[1];
}
You could create a private class and place the handler in there. E.g.
public void downloadphoto(string struri, string strtitle, string placeid)
{
using (WebClient wc = new WebClient())
{
wcHandler handler = new wcHandler() { Strtitle = strtitle, Placeid = placeid };
wc.DownloadDataCompleted += handler.wc_DownloadDataCompleted;
wc.DownloadDataAsync(new Uri(struri));
}
}
private class wcHandler
{
public string Strtitle { get; set; }
public string Placeid { get; set; }
public void wc_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
// Do Stuff
}
}
Although, given the elegance of Jon's answer would probably use that!
Jon Skeet already answered this, showing how to use a lamda expression, but I was still unclear about it. I still needed some more examples, and eventually found this simple case using a button: http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/74d03fe0-0fa5-438d-80e0-cf54fa15af0e
void A()
{
Popup parameter = new Popup();
buttonClose.Click += (sender, e) => { buttonClose_Click(sender, e, parameter); };
}
static void buttonClose_Click(object sender, EventArgs e, Popup parameter)
{
MakeSomethingWithPopupParameter(parameter);
}
In my case, I was using a context menu for a TreeView control, which ended up looking like this:
private void TreeViewCreateContextMenu(TreeNode node)
{
ContextMenuStrip contextMenu = new ContextMenuStrip();
// create the menu items
ToolStripMenuItem newMenuItem = new ToolStripMenuItem();
newMenuItem.Text = "New...";
// add the menu items to the menu
contextMenu.Items.AddRange(new ToolStripMenuItem[] { newMenuItem });
// add its event handler using a lambda expression, passing
// the additional parameter "myData"
string myData = "This is the extra parameter.";
newMenuItem.Click += (sender, e) => { newMenuItem_Click(sender, e, myData); };
// finally, set the node's context menu
node.ContextMenuStrip = contextMenu;
}
// the custom event handler, with "extraData":
private void newMenuItem_Click(object sender, EventArgs e, string extraData)
{
// do something with "extraData"
}