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Is it possible to detect if event has any listeners? (I need to dispose my event provider object, if nobody needs it)
489
To check whether dynamically attached event listener exists or not with JavaScript, we can get and set the element's listener attribute. export const attachEvent = ( element: Element, eventName: string, callback: () => void ) => { if (element && eventName && element. getAttribute("listener") !== "true") { element.
To check if an element was clicked, add a click event listener to the element, e.g. button. addEventListener('click', function handleClick() {}) . The click event is dispatched every time the element is clicked. Here is the HTML for the examples in this article.
To remove all event listeners from an element: Use the cloneNode() method to clone the element. Replace the original element with the clone. The cloneNode() method copies the node's attributes and their values, but doesn't copy the event listeners.
Assume the class is in a 3rd party library and it can't be modified:
public class Data
{
public event EventHandler OnSave;
//other members
}
In your program:
Data d = new Data();
d.OnSave += delegate { Console.WriteLine("event"); };
var handler = typeof(Data).GetField("OnSave", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(d) as Delegate;
if (handler == null)
{
//no subscribers
}
else
{
var subscribers = handler.GetInvocationList();
//now you have the subscribers
}
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