Index out of Range error when creating sections in TableView

问题

I have TableView inside a ViewController that is populated using JSON data:

The following is the structure of the JSON including sections:

struct TabSections {
    let name : String
    let collection : [TabCollection]
}

struct TabCollection: Decodable {
    let number, person, status: String
    let maker: String
}

The following is how the TableView and tabs populate with the JSON data:

var sections = [TabSection]()

private func fetchJSON() {
    guard let url = URL(string: "https://example.com/example/example.php"),
        let value = name.addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed)
        else { return }

    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.httpBody = "name=\(value)".data(using: .utf8)

    URLSession.shared.dataTask(with: request) { data, _, error in
        guard let data = data else { return }


        do {
            let decoder = JSONDecoder()
            decoder.keyDecodingStrategy = .convertFromSnakeCase
            let res = try decoder.decode([TabCollection].self, from: data)
            let grouped = Dictionary(grouping: res, by: { $0.status })
            let keys = grouped.keys.sorted()
            self.sections = keys.map({TabSections(name: $0, collection: grouped[$0]!)})

            DispatchQueue.main.async {
                self.receiptTableView.reloadData()
            }
        }
        catch {
            print(error)
        }

        }.resume()

}

The error occurs under numberOfRowsInSection and stops on the first line where section is defined:

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    let section = sections[section]

    return section.collection.count


}

I cannot seem to understand why I receiving Index out of range on the line let section

回答1:

Most likely you don't have a numberOfSections method which means the table view defaults to 1 section. Since your data model can have no elements initially, you need to implement numberOfSections to return the number of elements in sections.

override func numberOfSections(in tableView: UITableView) -> Int {
    return sections.count
}

回答2:

You can use that extension for Collection fo safely retrieving an element from collection.

extension Collection {
    /// Returns the element at the specified index if it is within bounds, otherwise nil.
    subscript (safe index: Index) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }
}

So your numberOfRowsInSection will look like that:

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    guard let section = sections[safe: section] else { 
        return 0 
    }
    return section.collection.count
}

来源：https://stackoverflow.com/questions/57468112/index-out-of-range-error-when-creating-sections-in-tableview

标签

swift

tableview