Sectioning a tableview by dates from a dictionary

Question

I have a dictionary that contains a key/value pair of a Date that contains an array of my custom object Meals grouped together by the same dates.

Meal Object:

class Meal: NSObject, Codable {

var id: String?
var foodname: String?
var quantity: Float!
var brandName: String?
var quantityType: String?
var calories: Float!
var date: Date?
}

In my TableView:

var grouped = Dictionary<Date, [Meal]>()
var listOfAllMeals = [Meal]() //already populated

self.grouped = Dictionary(grouping: self.listOfAllMeals.sorted(by: { ($0.date ?? nilDate) < ($1.date ?? nilDate) }),
            by: { calendar.startOfDay(for: $0.date ?? nilDate) })

override func numberOfSections(in tableView: UITableView) -> Int {
    // #warning Incomplete implementation, return the number of sections
    return grouped.count
}

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    return Array(grouped.keys)[section] as! String //this throws a thread error
}

This allows users to upload a meal multiple times a day for future viewing and now I want to show the meals in a TableView sectioned by their dates and sorted already by the latest. How do I achieve that?

Answer 1

Create a struct for the sections

struct Section {
    let date : Date
    let meals : [Meal]
}

and map the grouped dictionary to an array of Section

var sections = [Section]()

let sortedDates = self.grouped.keys.sorted(>)
sections = sortedDates.map{Section(date: $0, meals: self.grouped[$0]!)}

You could add a date formatter to display the Date instance more meaningful.

The table view data source methods are

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

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {        
    return sections[section].date.description
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return sections[section].meals.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "foodCell", for: indexPath)
    let meal = sections[indexPath.section].meals[indexPath.row]
    ...

Note:

Consider to use less optionals and a struct rather than a NSObject subclass. Unlike NSCoding Codable does not require to conform to NSObjectProtocol. And never declare properties as implicit unwrapped optional.

Answer 2

In your datamodel, you take the dictionary that you have with one day per entry, take the keys as an array, and sort the array.

Your tableview has as many sections as that array has entries. You create the title of each section from the date. For every section, you take the array of meals from the dictionary, so each section has a different number of rows, and the data from eac row is taken from one row of the arrays.

For example, to get the data for section 3, row 5, you take the date from your array of dates at index 3, you lookup the date in the dictionary and get an array of meals, and the meal at index 5 provides the data.