[alpha] Add .bind(this) to method stored in provider state

[anthonyraymond]

Fix #393

[tifosiblack]

Could we merge this as it's a blocking issue

[emilshr]

Merging this PR will be great!
Even I am stuck with this blocking issue

My current config:
"@material-ui/core": "4.11.0"

I've been seeing people reporting this issue on alpha versions of MUI.
I'm reporting the same issue on 4.11.0 as well.

[tifosiblack]

Meanwhile I used a workaround :

class FixedSnackbarProvider<
  V extends keyof T,
  T extends Record<V, React.ComponentType<any>>,
> extends SnackbarProvider<V, T> {
  constructor(props: SnackbarProviderProps) {
    super(props)
    const { enqueueSnackbar, closeSnackbar } = (this.state as any).contextValue

    this.state = {
      ...this.state,
      contextValue: {
        enqueueSnackbar: enqueueSnackbar.bind(this),
        closeSnackbar: closeSnackbar.bind(this),
      },
    }
  }
}

[emilshr]

I have used this temporary fix and it works great!
Thanks @tifosiblack

[iamhosseindhv]

Thanks for your contribution ❤️ . You can download the fix by npm i notistack@alpha.