Change color of selectedRow in UIPickerView, also when rolling

问题

I have to change the color of the selected row in a UIPickerView.

I did managed to change the color, i know that the question already have several replies, anyway those do not satisfy me: with those implementation, the animation of the pickerview is glitchy and i don't like it.

This is the code of the current solution

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {

    var label: UILabel
    if view == nil {
      label = UILabel()
    } else if view is UILabel {
      label = view as! UILabel
    } else {
      label = UILabel()
    }

    let title: NSAttributedString
    if self.model?.selectedValue == row {
      title = UIPickerView.attributedString(with: .selectedRow, text: "\(model?.years[row] ?? 0)")
    } else {
      title = UIPickerView.attributedString(with: .unselectedRow, text: "\(model?.years[row] ?? 0)")
    }

    label.attributedText = title
    return label
}

And when the user scrolls, I reload the components.

But as you can see in the images below, when a user scroll, the green field moves and there is a fraction of seconds in which the green label is below the selector indicator and the selected row is black.

What I'd like to have is that everything inside the selector indicator is green while what outside keeps the default shades of grey.

How can I implement this?

回答1:

You should use attributedTitleForRow for this instead, no need to create your own label with an NSAttributedString. In your didSelectRow your reload all your components to be able to reset all colors and set the new selected one to green.

func pickerView(_ pickerView: UIPickerView, attributedTitleForRow row: Int, forComponent component: Int) -> NSAttributedString? {
    let color = (row == pickerView.selectedRow(inComponent: component)) ? UIColor.green : UIColor.black
    return NSAttributedString(string: self.model[row], attributes: [NSForegroundColorAttributeName: color])
}

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    pickerView.reloadAllComponents()
}

回答2:

You can simply use this code

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
    let label = view as? UILabel ?? UILabel()

    if pickerView.selectedRow(inComponent: component) == row {
        label.backgroundColor = UIColor.green
        label.frame = CGRect(x: 0, y: 0, width: 36, height: 36)
        label.layer.cornerRadius = 18
        label.layer.masksToBounds = true
        label.textColor = .white
        label.text = String(numbers[row])
        label.textAlignment = .center
    }else {
        label.layer.cornerRadius = 25
        label.frame = CGRect(x: 0, y: 0, width: 36, height: 36)
        label.layer.cornerRadius = 18
        label.layer.masksToBounds = true
        label.textColor = .white
        label.text = String(numbers[row])
        label.textAlignment = .center
    }
    return label
}

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    pickerView.reloadAllComponents()
}

回答3:

Better effects with performance a little bad.

extension ViewController: UIPickerViewDelegate{

    func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
        let info = BeatScalar.generalRates[row]
        let general = GeneralRateItem(info.cn, info.ita, info.val)
        // gray every row
        general.unselected()
        decorateView(pickerView, row: row)
        return general
    }


    // Here is the logic 
    func decorateView(_ picker: UIPickerView, row: Int){

        var frame = picker.frame
        frame.origin.y = frame.origin.y + frame.size.height * 0.42
        frame.size.height = frame.size.height * 0.16

        let mini = max(row-1, 0)
        //   19 is total number
        let maxi = min(18, row+1)
        for i in mini...maxi{
            if i != row, let item = picker.view(forRow: i, forComponent: 0) as? GeneralRateItem{
                let f = item.convert(item.frame, to: picker)
                if frame.intersects(f) == false{
                    // highlight the center row
                    item.selected()
                }
            }
        }
    }

    func pickerView(_ pickerView: UIPickerView, rowHeightForComponent component: Int) -> CGFloat {
        return 44
    }
}


extension ViewController: UIPickerViewDataSource{
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {       // 19 is total number
        return 19
    }
}

来源：https://stackoverflow.com/questions/47048600/change-color-of-selectedrow-in-uipickerview-also-when-rolling