feat(dialog): add beforeClose method

[willshowell]

Fixes #4647

[jelbourn]

This test checks that beforeClose occurred, but not when it occurred. I'd restructure to be like

let beforeCloseInvoked = false;
const beforeCloseHandler = () => {
  expect(overlayContainerElement.querySelector('md-dialog-container')).toBeDefined();
  beforeCloseInvoked = true;
});
...
viewContainerFixture.whenStable().then(() => {
  expect(beforeCloseCallback).toHaveBeenCalledWith('Bulbasaurus');
  expect(overlayContainerElement.querySelector('md-dialog-container')).toBeNull();
});

[willshowell]

@jelbourn update to the test has been made. Let me know if I misinterpreted your comment!

[jelbourn]

Just one style nit

[jelbourn]

Omit spaces inside braces

[jelbourn]

LGTM

[kdubious]

I must be missing something, but how do we cancel the close in beforeClose()?

[willshowell]

@kdubious check out #4647 (comment)

[kdubious]

@willshowell, thanks. I read it, but still have a point of confusion.

I'm trying to pass a DTO to a dialog. The dialog has a form (ReactiveForm) that displays the DTO, the user makes their edits, then clicks "Save." At that point, I want the parent component (it maintains a list of the objects being edited in the dialog) to be notified about the current state of the object, so that the parent can manage saving to a remote service. If unsuccessful, the parent would prevent the dialog from closing.

Is there another approach I should consider?

[willshowell]

@kdubious I probably should've linked to this thread #3460, particularly #3460 (comment). Basically beforeClose is simply for getting the close value before the closing animation, but does not allow for synchronous or asynchronous cancellation of the close. If you want to cancel closing of the dialog (via esc or clicking on the backdrop), then you'll want to use disableClose and manually subscribe to the backdrop click and keydown event streams.

It sounds like in your case, you need to run the async validation before the dialog actually closes. If communication with the parent component is the issue, try using a service.

[kdubious]

Thanks @willshowell. I ended up going with the service.

[wiikka]

@willshowell I really don't see any real use case for beforeClose as it is currently implemented? As requested it would make much more sense if you could cancel the close event (e.g. asking from user if he wants to discard the changes).

In that use case it doesn't matter where you get the close event (is it esc, backdrop click or even dialogRef.close()). You should be able to intercept all those and cancel the close if you wish?

[willshowell]

@wiikka one of the use cases for beforeClose that was mentioned in the original issue was when you don't care how the dialog was closed, and you don't care to prevent it, but you want to do something with the resulting value without having to wait for the animation to complete.

The conversation in #3460, and more specifically #3460 (comment), pretty much covers why an all-encompassing "prevent/cancel close" api wasn't chosen.

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