迅捷3-ViewController不取消选择UITableView中的选定行

Question

I have a tableview where the user is able to select multiple rows (these rows are distinguished by a checkbox in the row). For some reason, however, I can't implement the functionality to deselect any selected row. Can somebody tell me what I'm missing?

SomeViewController.m

@objc class SomeViewController: UIViewController, NSFetchedResultsControllerDelegate, UITableViewDataSource, UITableViewDelegate {

    var deviceArray:[Device] = []

    // [perform a fetch]
    // [insert fetch results into deviceArray to be displayed in the tableview]

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "customcell", for:
        indexPath)

        // Set up the cell
        let device = self.deviceArray[indexPath.row]
        cell.textLabel?.text = device.name

        return cell
    }

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        self.tableView(tableView, cellForRowAt: indexPath).accessoryType = UITableViewCellAccessoryType.checkmark
        NSLog("Selected Row")
    }

    func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
        self.tableView(tableView, cellForRowAt: indexPath).accessoryType = UITableViewCellAccessoryType.none
        NSLog("Deselected Row")
    }
}

More info: Looking at the debug logs inserted, I can share the following observations:

1. When selecting an unselected row, the console prints "Selected Row"

2. If I click the same row from observation #1, the console prints "Selected Row" only

3. If I click on any other row, the console prints "Deselected Row" and then "Selected Row"

4. If I click on the same row as observation #3, the console prints "Selected Row" only.

So, it looks like everytime I click on a different row, tableView: didDeselectRowAt: gets called; however, checkmarks in the clicked row do not go away.

More Info 2:

So I'm new to storyboards and didn't set the "allowsMultipleSelection" property. Going into the Attributes Inspector, this is what my settings look like:

Now, when pressing the same row in the tableView, my console confirms that the app is alternating between tableView:didSelectRowAt: and tableView:didDeselectRowAt:, however, the checkmark doesn't disappear; once the user selects a row, the checkmark remains selected even when tableView:didDeselectRowAt: is called. What else am I missing?

Answer 1

First off make sure your datasource AND delegate outlets are set if you are setting them from storyboard.

Another thing is you need to set allowsMultipleSelection property to true to get the didSelect , didDeselect methods to get called in the behavior you want. Otherwise it will always call didSelect for the cell you tapped on and didDeselect for the most previously selected cell.

The other thing to note is that you are referencing self.tableView when setting your cell.accessoryType property. This may be different instance of the tableView being passed into the delegate method. I recommend a guard let statment to ensure the code setting the accessory type only applies if the tableView being passed into the function. Here is code I used to get it to work.

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    //Notice I use tableView being passed into func instead of self.tableView
    guard let cell = tableView.cellForRow(at: indexPath) else {
        return
    }
    cell.accessoryType = .checkmark

}

func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
    guard let cell = tableView.cellForRow(at: indexPath) else {
        return
    }
    cell.accessoryType = .none
}

Answer 2

如果希望用户能够选择多个单元格，则需要在viewDidLoad方法中设置tableView.allowsMultipleSelection = true或在属性检查器中设置多个选择。