[BUG] code related to disableScrollToActiveOnOptionsChanged was removed

[kugelblitz-prog]

Describe the bug
Input disableScrollToActiveOnOptionsChanged solves issue #200
But for some reason the code that uses disableScrollToActiveOnOptionsChanged was removed in this commit 303107f
Now disableScrollToActiveOnOptionsChanged is not used anywhere in the code https://github.com/bithost-gmbh/ngx-mat-select-search/blob/master/src/app/mat-select-search/mat-select-search.component.ts

Expected behavior

disableScrollToActiveOnOptionsChanged should fix the scrolling bug described in #200

[macjohnny]

thanks for reporting

this was changed in e3976c2

setting [disableScrollToActiveOnOptionsChanged]="true" should have the same effect before and after the change, since it avoids "scrolling the currently active option into the view if it is not yet visible".

With the current state of the code, what problem are you experiencing and what is the proposed fix?

[kugelblitz-prog]

Sorry, I found the problem.

In my project, I had [disableScrollToActiveOnOptionsChanged] set to true, so I was confused when I noticed that the list automatically scrolls to the top during infinite scroll. As a result, I created this issue.

After thoroughly examining your code, I found this piece of code:

    // set the first item active after the options changed
    this.matSelect.openedChange
      .pipe(
        take(1),
        switchMap(() => {
        this._options = this.matSelect.options;

        // Closure variable for tracking the most recent first option.
        // In order to avoid causing the list to
        // scroll to the top when options are added to the bottom of
        // the list (eg: infinite scroll), we compare only
        // the changes to the first options to determine if we
        // should set the first item as active.
        // This prevents unnecessary scrolling to the top of the list
        // when options are appended, but allows the first item
        // in the list to be set as active by default when there
        // is no active selection
        let previousFirstOption = this._options.toArray()[this.getOptionsLengthOffset()];

        return this._options.changes
          .pipe(tap(() => {
            // avoid "expression has been changed" error
            setTimeout(() => {
              // Convert the QueryList to an array
              const options = this._options.toArray();

              // The true first item is offset by 1
              const currentFirstOption = options[this.getOptionsLengthOffset()];

              const keyManager = this.matSelect._keyManager;
              if (keyManager && this.matSelect.panelOpen && currentFirstOption) {

                // set first item active and input width

                // Check to see if the first option in these changes is different from the previous.
                const firstOptionIsChanged = !previousFirstOption
                  || !this.matSelect.compareWith(previousFirstOption.value, currentFirstOption.value);

The key part is this line:
const firstOptionIsChanged = !previousFirstOption || !this.matSelect.compareWith(previousFirstOption.value, currentFirstOption.value);

In my project, I used a custom compareWith function but did not account for possible null values. As a result, firstOptionIsChanged was always evaluated as true in my project.

[macjohnny]

@kugelblitz-prog so can we close this issue?

[kugelblitz-prog]

@macjohnny up to you. The disableScrollToActiveOnOptionsChanged input does not do anything, and it's confusing. Maybe someone can remove this input and link the removal to this issue?

[macjohnny]

@kugelblitz-prog would you want to remove the input and file a PR? if so, please also update the readme