Swift 3 UITableViewCell indexPath.row搞砸了

Question

I have a TableView to show bunch of movies in. movies is the array of Movie objects. movieIDs is the array of movie ids. Ids are just strings.

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "movieCell", for: indexPath) as! MovieCell

        // editing the cell here.

        cell.movieNameLabel.text = movies[indexPath.row].movieName
        cell.movieYearLabel.text = movies[indexPath.row].year

        // source of all hell here.

        for id in movieIDs {

            if id == movies[indexPath.row].movieID {

                print(id + " is equal to " + movies[indexPath.row].movieID)
                cell.myButton.setImage(/*there is an image here*/), for: .normal)

            }

        }

The for loop in cellForRowAt method:

for id in movieIDs {

        if id == movies[indexPath.row].movieID {

            print(id + " is equal to " + movies[indexPath.row].movieID)
            cell.myButton.setImage(//there is an image here), for: .normal)
        }

    }

I am comparing all the ids in the movieIDs to the id of the movie at the cell, which is movies[indexPath.row].movieID . If it returns true, i replace the image of the button inside the cell. When i print inside the if statement, it actually doesn't execute but it still replaces button images at random cells. And if i scroll too fast up and down, images of the buttons gets replaced in almost all cells, when its only intended to change for cells that ids match.

Answer 1

The reason that the cells are stuffed up is because they are reusable cells.

So for example, if you have cell #1 set up with an image, when you scroll down and that cell #1 goes off the screen and becomes cell #10 (for instance), it is still showing the image.

The solution is you have to remove the image that was previously set by checking if it doesn't match the movieID , set the image to nil .

You don't have to do the for loop here, instead you use the contains for array. So replace this code:

for id in movieIDs {

    if id == movies[indexPath.row].movieID {

        print(id + " is equal to " + movies[indexPath.row].movieID)
        cell.myButton.setImage(//there is an image here), for: .normal)
    }

}

with this:

if movieIDs.contains(movies[indexPath.row].movieID) {
    cell.myButton.setImage(//there is an image here), for: .normal)
}
else{
    cell.myButton.setImage(nil)
}

Answer 2

You have to set nil if no id matches:

var matched = false
for id in movieIDs {

    if id == movies[indexPath.row].movieID {

        print(id + " is equal to " + movies[indexPath.row].movieID)
        cell.myButton.setImage(//there is an image here), for: .normal)
        matched = true
    }

}

if !matched {
    cell.myButton.setImage(nil)
}

For a better solution, you should create a function to get the image:

if let image = getMovieImageByID(movies[indexPath.row].movieID) {
    cell.myButton.setImage(image), for: .normal)
} else {
    cell.myButton.setImage(nil), for: .normal)
}

func getMovieImageByID(movieID: String) -> UIImage? {
    for id in movieIDs {
        if id == movieID {
            // return the image for the respective movieID
        }
    }

    return nil
}