為什么 swift UIPickerView 會多次調用委托 numberOfComponents 和 numberOfRowsInComponent？

Question

是我的輸出，每次調用委托時都會打印。

為什么是多個： numberOfComponents 和 numberOfRowsInComponent ？

open_plot_picker()...
numberOfComponents: 1
numberOfComponents: 1
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfComponents: 1
numberOfRowsInComponent: 6
titleForRow: raw heart beat only    row 0
titleForRow: filtered heart beat only    row 1
open_plot_picker() done.
select_plots_UIButton() done.
numberOfComponents: 1
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
titleForRow: raw heart beat only    row 0
titleForRow: filtered heart beat only    row 1
numberOfRowsInComponent: 6
numberOfRowsInComponent: 6
titleForRow: raw heart beat only    row 0
titleForRow: filtered heart beat only    row 1
titleForRow: heart rates only    row 2
titleForRow: raw HB and HR     row 3
titleForRow: filtered HB and HR    row 4
titleForRow: filtered and raw HB    row 5
numberOfRowsInComponent: 6
titleForRow: raw heart beat only    row 0

Answer 1

你不應該關心你的委托方法被調用的頻率。 看起來它一遍又一遍地向您的代表詢問行數。 只要確保代碼是高性能的，不要擔心。