Strange behavior in events

[uazo]

Example:

@for( var page = FirstPage; page <= LastPage; page++ )
{
	<li class="@(this.Values.CurrentPage==page ? "active" : "page-item")">
		<a href="javascript:;" class="page-link" @onclick(() => InvokePageChanged(page))>@(page+1)</a>
	</li>
}

The value of "Page" in InvokePageChanged is always "LastPage".

The only way to make it work is:

@for( var page = FirstPage; page <= LastPage; page++ )
{
	int current = int.Parse(page.ToString());
	<li class="@(this.Values.CurrentPage==page ? "active" : "page-item")">
		<a href="javascript:;" class="page-link" @onclick(() => InvokePageChanged(current))>@(page+1)</a>
	</li>
}

[rstropek]

As far as I can see, only your working solution turns the lambda function invoking InvokePageChanged into a closure capturing the value of page. See e.g. this StackOverflow post for a more detailed description of the topic.

Does that help?

[uazo]

I had already tried with

@for( var page = FirstPage; page <= LastPage; page++ )
{
	int current = page;
	<li class="@(this.Values.CurrentPage==page ? "active" : "page-item")">
		<a href="javascript:;" class="page-link" @onclick(() => InvokePageChanged(current))>@(page+1)</a>
	</li>
}

but it does not work..

the only way is to turn it into a string.
Maybe some optimization of the compiler?

[rstropek]

Hmm, I tried that and it worked:

@for (var page = 0; page <= 5; page++)
{
    var helper = page;
    <button @onclick(() => InvokePageChanged(helper))>@(helper)</button>
}

@functions {
    void InvokePageChanged(int page)
    {
        Console.WriteLine(page);

    }
}

I also expected it to work because the generated code looks like that:

...
for (var page = 0; page <= 5; page++)
{
    var helper = page;
    ...
    builder.AddAttribute(13, onclick(() => InvokePageChanged(helper)));
    ...
}
...

[SteveSandersonMS]

Yes, I also just tried that and confirmed it works OK. There's no need to do the conversion to string and back again.

The necessity to declare a variable inside your loop is just how C# lambdas work - they bind to a variable, not to the value that was in the variable when the lambda was constructed. The StackOverflow that @rstropek linked to is a good source of info about this. Also note how it's different if you use foreach instead of for, because foreach logically declares a new variable for each iteration.