RxSwift + UITableViewCell how to get cell object in heightForRowAt

问题

I have a view controller with UITableView. The table data is populated using RxSwift:

let observable = Observable.just(data)
observable.bindTo(tableView.rx.items(cellIdentifier: "CategoryCell", cellType: CategoryCell.self)) { (row, element, cell) in
    cell.setCategory(category: element)
}.disposed(by: disposeBag)

tableView.rx.setDelegate(self).disposed(by: disposeBag)

and I have the following delegate function:

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    // cell = nil. 
    let cell = tableView.cellForRow(at: indexPath)

    let screenWidth = UIScreen.main.bounds.size.width

    let itemWidth = (screenWidth / 3.0) - 20
    let itemHeight = (itemWidth) / 0.75 + 110

    return itemHeight
}

I want to access the cell object from inside heightForRowAt but it gives me nil. Is there a way to access the cell here? I have been looking at UITableView+Rx.swift in RxCocoa project but there is no function for this. What other options do I have?

EDIT: I am trying to achieve the following in my code:

class CategoryCell : UITableViewCell {
     func calculateHeight() {
        let screenWidth = UIScreen.main.bounds.size.width

        let itemWidth = (screenWidth / 3.0) - 20
        let itemHeight = (itemWidth) / 0.75 + 110

        return itemHeight
     }
}

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    // cell = nil. 
    guard let cell : CategoryCell = tableView.cellForRow(at: indexPath) as? CategoryCell {
         return 0.0
    }
    return cell.calculateHeight()
}

回答1:

The call tableView.cellForRow(at: indexPath) returns nil in tableView(_: heightForRowAt:) because heightForRowAt is called on a particular indexPath before the cellForRowAt is called.

The best bet here would be to use self-sizing cells. (https://www.raywenderlich.com/129059/self-sizing-table-view-cells). Another option would be to keep the size of the cells as part of your model and access them here.

来源：https://stackoverflow.com/questions/43015448/rxswift-uitableviewcell-how-to-get-cell-object-in-heightforrowat