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Query 1: Hierarcial and conitnuous scrolling onDemand loadings.
Currently there is no support for load-on demand feature in Treegrid control, but it has built-in support to render large data along with multi-level hierarchies in virtualization approach by using “EnableVirtualization” property. In virtualization mode the Treegrid control renders or we can able to visualize only few elements of data at a time ,depending upon the height of the Treegrid control (viewport/view height) , thereby increasing the responsiveness in Treegrid while scrolling, expanding ,collapsing and other such actions . In virtualization concept, the scrollbar or scroller of Treegrid is intended to render as if there are large data, as in your case 1000 elements for instance, but actually the elements which are viewable alone are rendered, even while scrolling the Treegrid content. You can achieve the virtualization in Treegrid with below code snippet ,
We have also prepared a sample based on this and you can find the sample under the following location
Query 2: Support for begin with all hierarchies open (I think that this is already possible but just saying)
Solution: By default while loading the TreeGrid all the parent items will be in expanded state . We can also expand all or collapse all the items dynamically with the help of toolbar action.
Please let us know if you need further assistance on this.