UIPickerView為什么不顯示行？ 迅速

Question

我正在嘗試使用2個組件制作單個UIPickerView，每個組件具有不同數量的行。 我以為可以在每個組件的索引上建立每個組件的行號，但是當我運行我的應用程序時，UIPickerView僅顯示一個空白行，並且不允許滾動。

func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
    return 2
}

// grades is a 2D array
func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    return grades[component].count
}

// level and letter are predefined ints
func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    if component == 0 {
        level = row
    }else if component == 1 {
        letter = row
    }
    return ""
}

編輯：

這是我的viewDidLoad（）

override func viewDidLoad() {
    super.viewDidLoad()
    pickerView.dataSource = self;
    pickerView.delegate = self;
}

Answer 1

我相信您應該返回非空標題以使其起作用

...

// level and letter are predefined ints

func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {

    if component == 0 {
        level = row
    } else if component == 1 {
        letter = row
    }
    return "Component: \(component) Row: \(row)" // whatever string you want to display
}