Hello Ishani,

Thank you for posting in our community.
What I can suggest for achieving your requirement is working with hierarchicalState property  that IgxHierarchicalGridComponent class provides. This is an array consisting of all toggled rows. The state of this collection can be tracked for any changes. When such a change occurs, this means that a row was toggled. This row was either expanded or collapsed, however, in both cases the hierarchicalState array is updated. A working sample illustrating my suggestion can be found here.

https://stackblitz.com/edit/angular-6byo8k

What we have in this sample is an iterable needed to determine changes in the hierarchicalState array. It is created into the constructor of the component and is used at later stage to initialize a differ (See angular.io/.../IterableDiffer for reference). The differ could be used to determine whether the array of toggled rows has changed. Having this, one could easily determine which rows are collapsed, expanded etc.

Please do not hesitate to contact me if you need any further assistance. 

Best regards,
Petko

Thanks for coming back to me!
NgDoCheck is the way to actually watch for a change in a collection, so if you are just trying to mock such an event, that’s the way.
If you’d like to provide the grid with data on demand, you may wish to get to know the Hierarchical Grid's Load on Demand Feature, which allows you to use onGridCreated event.
If that’s not the case, please send me a sample and a detailed description of what you’d like to achieve.

Thank you,
Petko Bozhinov