UIPickerView重用視圖總是爲零

Question

據蘋果API引用在此方法中

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

重用視圖由選擇器視圖緩存看法，但是當我試圖使用它的下一行，它總是零，而我當重複使用視圖爲零時，返回UILabel。問題是什麼？ 這是我的實現：

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView { 
    let pickerLabel = UILabel() 
    pickerLabel.textColor = UIColor.black 
    pickerLabel.text = "10" 
    pickerLabel.textAlignment = NSTextAlignment.center 
    pickerLabel.sizeToFit() 
    return pickerLabel 
} 

Answer 1

您的代碼不會嘗試使用重用視圖。您的代碼應該是這樣的：

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView { 
    var pickerLabel : UILabel 
    if let label = view as? UILabel { 
     pickerLabel = label 
    } else { 
     pickerLabel = UILabel() 
     pickerLabel.textColor = UIColor.black 
     pickerLabel.textAlignment = NSTextAlignment.center 
    } 

    pickerLabel.text = "10" 
    pickerLabel.sizeToFit() 

    return pickerLabel 
} 

如果重用視圖是標籤，此代碼會重用標籤。否則，它會創建並設置一個新標籤。

請注意，選取器只會在選取器視圖滾動時通過重用視圖。它類似於表格視圖的單元重用。