how to determine if EventHandler has a Event?

[ljzj2]

there is Button and I will set to it.
button.Click+=(sender,e)=>{

}

if I run it twice it will run the code twice.
since it bind two code.

how to determine the button has a event so I do not run the code?

[jonathanpeppers]

So, this is a general C# question:

• I have a C# event, how prevent the code from "double subscribing"?

One way is to do:

button.Click -= OnClick;
button.Click += OnClick;

void OnClick (object sender, EventArgs e)
{

}

.NET MAUI takes this approach in a few places.

But there are lots of different ways you could do it:

1. Best: subscribe in a place that is called once. Example: OnCreate()
2. Alternatively, to the example above, you could use a bool member variable to track if you've subscribed.

Hope that helps, thanks!