Swift：致命错误：从TableView删除项目时数组索引超出范围

Question

I've setup a table to pull data from a database. The user can manually delete items from the table (and thus the database) via checkbox (table.editing = true, iirc) and a delete button. This can be done one at a time, or all at a time.

Unfortunately, whenever I check everything for deletion, the app crashes with the following error:

fatal error: Array index out of range

This does not happen if I select and delete only one or any number of the table rows, as long as I don't select everything.

Here's my code for the delete button:

func deleteButtonPressed(sender: AnyObject) {
    if (self.pureSteamFormView.tableCalibration.editing == true) {
        if (self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows!.count >= 1) {
            for indexPath in self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows!.sort({ $0.row < $1.row}) {
                let calibTable : FormSteamPurityCalibration = self.steamPurityCalibrationTableList[indexPath.row] /* <--- ERROR HERE */

                DatabaseManager.getInstance().deleteData("FormSteamPurityCalibration", "ID = \(calibTable.ID)")

                self.steamPurityCalibrationTableList.removeAtIndex(indexPath.row)
            }
            self.pureSteamFormView?.tableCalibration.reloadData()
        }
    }
}

Near as I can figure, it is attempting to remove the row at an index, an index that may no longer exist (?) due to the previous row also being deleted, but I'm not sure about that.

I tried putting the following code:

self.steamPurityCalibrationTableList.removeAtIndex(indexPath.row)

In its own for-loop block, and the error promptly move there.

I also tried removing the removeAtIndex part completely, relying on the reloadData() to perhaps update the table automatically, but it doesn't work - the data is deleted from the database, but remains on the table (although moving away from that view and going back there updates the table).

Any suggestions please? Thanks.

Answer 1

Your problem here is that you are deleting the lowest indexes before the bigger ones. Let me explain with an example:

Image you have 4 elements in your array:

let array = ["Element1", "Element2", "Element3", "Element4"]

You are trying to remove the elements at index 1 et 3:

for index in [1, 3] {
    array.removeAtIndex(index)
}

Your program will first remove element at index 1, leaving you with the following array:

["Element1", "Element3", "Element4"]

On the second pass of the loop it will try to remove the element at index 3. Which does not exist anymore because it has moved to index 2.

One solution to this is to start removing element with the greater index before, so in your code you could change

for indexPath in self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows!.sort({ $0.row < $1.row}) {

to

for indexPath in self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows!.sort({ $0.row > $1.row}) {

A better solution would be to filter your data array to include only the elements you whish to keep, so instead of:

for indexPath in self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows!.sort({ $0.row < $1.row}) {
    let calibTable : FormSteamPurityCalibration = self.steamPurityCalibrationTableList[indexPath.row]
    DatabaseManager.getInstance().deleteData("FormSteamPurityCalibration", "ID = \(calibTable.ID)")
    self.steamPurityCalibrationTableList.removeAtIndex(indexPath.row)
}

you could do:

self.steamPurityCalibrationTableList.filter {
    if let index = self.steamPurityCalibrationTableList.indexOf ({ $0 })
    {
        for indexPath in self.pureSteamFormView.tableCalibration.indexPathsForSelectedRows! {
            if indexPath.row == index { return false }
        }

        return true
    }
}