I am drawing a tableview via BehaviorRelay.
Currently, I am using the code below as a way to add data.
viewModel.user.append(Person(name: "king", phoneNumber: "12341234"))
viewModel.personObservable.accept(viewModel.user)
I wonder if this code changes the user itself so that the whole tableView is redrawn. If so, what method can I use to change only the data I added?
The code presented causes the personObservable (which is actually a BehaviorRelay apparently,) to emit a next event that contains an entire array of Person values, not just the latest Person added. Importantly, it's not emitting the viewModel.user object (at least not conceptually) but an entirely different object that happens to be equal to viewModel.user.
The default dataSource, the one that you get when you call items with anything other than a DataSource object, will call reloadData on the table view. This doesn't cause "the whole tableView" to be redrawn though, but it will cause the table view to query the data source for all of the visible cells, even if they haven't changed.
If you only want the table view to load the new cell, then the data source object needs to be smart enough to compare the new array with the array it's currently displaying so it can figure out which values are different and add/remove/move cells as appropriate, instead of just calling reloadData. As @Sweeper said in the comments, the RxDataSources library contains a set of data source classes that have that logic built in. If you wanted to reinvent the wheel, just write a class that conforms to both RxTableViewDataSourceType & UITableViewDataSource and implement the diffing yourself.