Method _switchDataSource

src/cdk/tree/tree.ts:344–361

* Switch to the provided data source by resetting the data and unsubscribing from the current * render change subscription if one exists. If the data source is null, interpret this by * clearing the node outlet. Otherwise start listening for new data.

(dataSource: DataSource<T> | Observable<T[]> | T[])

   * clearing the node outlet. Otherwise start listening for new data.
   */
  private _switchDataSource(dataSource: DataSource<T> | Observable<T[]> | T[]) {
    if (this._dataSource && typeof (this._dataSource as DataSource<T>).disconnect === 'function') {
      (this.dataSource as DataSource<T>).disconnect(this);
    }

    this._dataSubscription?.unsubscribe();
    this._dataSubscription = undefined;

    // Remove the all dataNodes if there is now no data source
    if (!dataSource) {
      this._nodeOutlet.viewContainer.clear();
    }

    this._dataSource = dataSource;
    if (this._nodeDefs) {
      this._subscribeToDataChanges();
    }
  }

  _getExpansionModel() {
    if (!this.treeControl) {