fix(ng-maxLength): rerender mdMaxLength when ngModel is updated in the controller

[josefromsanjose]

This issue comes up when sharing one form for several models. For example a list. If you were to click on one item that displays the form and it has a value for the scope variable being counted, it works fine. But if you change to a different list item that does not have a value, mdMaxLength keeps the count from the previous model, but the input is empty.

[crisbeto]

I believe you could achieve the same without using a watcher by doing ngModelCtrl.$parsers.push(renderCharCount); here. Also it would be nice if you could add a unit test for this so it doesn't get broken in the future.

[josefromsanjose]

@crisbeto that was my first approach but it did not work. The problem still persists.

[crisbeto]

Alright, you should still be able to reduce it to scope.$watch(attr.ngModel, renderCharCount). Also can you rename your commit and PR so they match the format of the other PRs?

[josefromsanjose]

@crisbeto I renamed to PR but could not rename the commits. Moving forward I will make sure I check what commit titles look like. This is my first open source contribution.

[devversion]

I'm sorry, that I created something like a second approach, but your PR wasn't referencing the issues properly. So there is a more generic / universal solution now.

See #8351

cc. @crisbeto

[crisbeto]

Yeah that definitely looks better.

[crisbeto]

@josefromsanjose Thank you for the PR, but I'll have to close it, because @devversion's solution solves the problem in a better way, removes a bunch of event listeners and has unit tests.