I have a silverlight mvvm application that loads main view with 2 user controls loaded into 2 ContentControls, one with listbox showing items and other with edit button. When i click edit button, 2 new user controls load into the ContentControls, one showing data to edit (EditData) and other having Save and Cancel button (EditAction).
When i click save button, it raises an event that is defined in seperate GlobalEvents.cs class like:
public event EventHandler OnSaveButtonClicked;
public void RaiseSaveButtonClicked()
{
this.OnSaveButtonClicked(this, EventArgs.Empty);
}
and i subscribe to it in the other user control EditData, because i need to transfer that edited data via custom EventArgs, so i have put in the constructor of it's ViewModel:
this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData();
and in the Save data:
public void SaveData()
{
globalEvents.RaiseSaveData(EditedGuy);
}
which raises another event that loads previous user controls into their ControlContent and shows edited data in list box. Thats all fine, but whenever i click on edit and then save again, it raises the event twice, and again 3 times, then 4 and so on. How can i make it to be raised only ONE time? I thought it could be because every time i click edit, a new instance of the user control is loaded and i dont know, maybe the subscription to the event stays, so i have tried to paste
this.globalEvents.OnSaveButtonClicked -= (s, e) => SaveData();
to the Dispose() method but without success. How can i make this work?
You can't use lambdas when you want to unregister from events.
this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData();
This will create one instance - let's call it instance A - of type EventHandler and add it as a handler.
this.globalEvents.OnSaveButtonClicked -= (s, e) => SaveData();
This will not remove instance A from the event but create a new instance - instance B - and tries to remove it from the event.
To fix this problem, either create a little method or save that anonymous method in a field:
class ViewModel
{
private EventHandler _saveButtonClickedHandler;
// ...
public ViewModel()
{
_saveButtonClickedHandler = (s, e) => SaveData();
this.globalEvents.OnSaveButtonClicked += _saveButtonClickedHandler;
// ...
}
public void Dispose()
{
this.globalEvents.OnSaveButtonClicked -= _saveButtonClickedHandler;
// ...
}
// ...
}
this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData();
This line is being called multiple times so you are adding a new event handler every time.
You need to either move that line to somewhere where it's only called once or change the event handler to:
this.globalEvents.OnSaveButtonClicked += SaveData;
public void SaveData(object sender, EventArgs e)
{
globalEvents.RaiseSaveData(EditedGuy);
this.globalEvents.OnSaveButtonClicked -= SaveData();
}
So you remove the event handler after dealing with it. This assumes that the handler will be added back next time you go into edit mode.
You could define a private eventhandler delegate variable in your class and assign it in your constructor:
private SaveButtonClickedHandler _handler;
Assign the handler in your constructor:
_handler = (s,e) => SaveData();
this.globalEvents.OnSaveButtonClicked += _handler;
Dispose:
this.globalEvents.OnSaveButtonClicked -= _handler;
"SaveButtonClickedHandler" is pseudo-code/placeholder for whatever the name of the delegate should be.
Hasanain
You'll have to put in a proper event handler method that calls SaveData() and register/unregister that. Otherwise you try to unregister another "new" anonymous method instead of the original one you've registered, which you, because it is anonymous, cannot actually access anymore.
public void SaveButtonClicked(object sender, EventArgs e)
{
SaveData();
}
this.globalEvents.OnSaveButtonClicked += SaveButtonClicked;
this.globalEvents.OnSaveButtonClicked -= SaveButtonClicked;
Related
Exactly where I must write this code?
button1.MouseHover += Common_MouseHover;
The problem is I want to declare one event handler and point each button at it. This is the common handler:
private void Common_MouseHover(object sender, EventArgs e)
{
Button btn = sender as Button;
if (btn != null)
btn.Image = pic
}
But I dont know where i must write:
button1.MouseHover += Common_MouseHover;
utton2.MouseHover += Common_MouseHover;
.. etc
In designer? Where exactly?
Either in the designer or the Constructor of your Form or if you are creating dynamic Buttons at the time of creation.
public Form1()
{
InitializeComponent();
button1.MouseHover += new EventHandler(Common_MouseHover);
button2.MouseHover += new EventHandler(Common_MouseHover);
}
If in the Property Editor.
Technically, it depends when you want to assign it. For example, you might not want the event to be handled by that method until certain conditions are met: then you assign the event handler once the conditions are true.
Bear in mind that assigning event handlers can cause memory leaks if you aren't careful. For example, you might have a timer that continually assigns the same event handler to the event. You need to check if the event already has the event handler, or if it's null, or whatever you need to prevent duplication. You might also want to remove event handlers dynamically using the -= operator.
For the example given, the form's constructor seems right, and is the most common place for assigning event handlers manually.
Call following function in your form Constructor after InitializeComponent(); -
private void init()
{
foreach (Control ctrl in this.Controls)
{
if (ctrl is Button)
{
(ctrl as Button).MouseHover += new EventHandler(Common_MouseHover);
}
}
}
Call it like this -
// Form Constructor
public Form3()
{
InitializeComponent();
Init();
}
I wish to programatically unsubscribe to an event, which as been wired up.
I wish to know how I can unsubscribe to the EndRequest event.
I'm not to sure how to do this, considering i'm using inline code. (is that the correct technical term?)
I know i can use the some.Event -= MethodName to unsubscribe .. but I don't have a method name, here.
The reason I'm using the inline code is because I wish to reference a variable defined outside of the event (which I required .. but feels smelly... i feel like I need to pass it in).
Any suggestions?
Code time..
public void Init(HttpApplication httpApplication)
{
httpApplication.EndRequest += (sender, e) =>
{
if (some logic)
HandleCustomErrors(httpApplication, sender, e,
(HttpStatusCode)httpApplication.Response.StatusCode);
};
httpApplication.Error += (sender, e) =>
HandleCustomErrors(httpApplication, sender, e);
}
private static void HandleCustomErrors(HttpApplication httpApplication,
object sender, EventArgs e,
HttpStatusCode httpStatusCode =
HttpStatusCode.InternalServerError)
{ ... }
This is just some sample code I have, for me to handle errors in a ASP.NET application.
NOTE: Please don't turn this into a discussion about ASP.NET error handling. I'm just playing around with events and using these events for some sample R&D / learning.
It's not possible to unsubscribe that anonymous delegate. You would need to store it in a variable and unsubscribe it later:
EndRequestEventHandler handler = (sender, e) =>
{
if (some logic)
HandleCustomErrors(httpApplication, sender, e,
(HttpStatusCode)httpApplication.Response.StatusCode);
};
httpApplication.EndRequest += handler;
// do stuff
httpApplication.EndRequest -= handler;
I have an application and I want to start a countdown timer.
I created an EventHandler under the partial class:
event EventHandler startTimer;
And I wrote a function:
public void startTimerEvent(object sender, EventArgs e)
{
this.Invoke((MethodInvoker)delegate
{
timer.Start();
});
}
How can I register this to the EventHandler and where do I wire it up in my form?
To tie the event to the handler:
startTimer += startTimerEvent;
But I'm not really sure there isn't a better way to go about solving your general problem. If you could describe further what you're after, perhaps we could suggest a better way.
So you need to choose an event that will trigger your handler. Let’s say you have a button, and you want to handle its click event. You could write:
myButton.Click += new EventHandler(StartWhatEver);
Then you would have your StartWhatEver that does what you want.
private void StartWhatEver(object sender, EventArgs e)
{
// Do stuff...
}
Note: If you are working in VS2010, you can type myButton.Click += (with space) then double tap the 'Tab' key and this will create your handler for you automatically including the triggered method.
Hope this helps.
I've set an eventhandler to an event like this:
frm.FormClosed += (sender, args) =>
{
if (this.myGrid.Enabled)
{
this.myGrid.Select();
}
};
frm.Show();
I want to hang out the eventhandler after the form was closed.
Can you help me?
I want to hang out the eventhandler after the form was closed.
I assume you want to remove it.
Not necessary, don't waste time on it. When the Form is closed (and Disposed), the eventhandler will be collected too. It is a member of the same Form, that follows from the word this in the code.
If you still want to remove it, you will need a copy:
FormClosedEventhandler closeHandler; // class member
closeHandler = (sender, args) =>
{
if (this.myGrid.Enabled)
{
this.myGrid.Select();
}
};
frm.FormClosed += closeHandler ; // OnLoad
...
frm.FormClosed -= closeHandler ; // OnClose
If you mean how to remove you event handler from the event, then you won't be able to use an anonymous delegate but you can create a method with the same parameters and same code and then:
private void EventHandler(object sender, FormClosedEventArgs e)
{
if (this.myGrid.Enabled)
{
this.myGrid.Select();
}
}
frm.FormClosed += EventHandler; // Attach the event handler
frm.FormClosed -= EventHandler; // Remove the event handler
PREFACE
I have a Windows form Button that exposes the event OnClick (object sender, EventArgs e).
In my application I can handle this by using the classic event handling technique of C#:
// Button Creation
Button button = new Button();
button.Click += MyEventHandler;
Then Windows Form ask me for an handler with the following signature:
public void MyEventHandler(object sender, EventArgs e) { }
Suppose that I would like to use lambda expression to do this I can use the syntax:
button.Click += (sender, args) =>
{
// execute the code
};
The drawback of this is that I can't unsubscribe from a Lambda expression.
QUESTION
What I would like to do is to have an utility class that will allow me to handle any Click event plus using an additional Action as a parameter. So I would like to write something like this:
button.Click += MyUtility.Click(()
=> {
// the custom code the Click event will execute
})
Can I do it in somehow?
You can assign the lambda expression to a local variable or field.
For example:
EventHandler handler = (sender, args) =>
{
// execute the code
};
button.Click += handler;
button.Click -= handler;
If you want to unsubscribe inside the handler, you'll need to assign handler to null, then to the lambda, to avoid definite assignment issues.