UIPickerView numberOfRowsInComponent运行三次

Question

我有一个类，其中我对多个textField使用单个pickerView，效果很好。 我还设置了条件if the array that is being used for pickerView's dataSource is empty, fire a function to show an alert。糟糕的是，numberOfRowsInComponent运行三次，而警报功能也运行三次。我不知道为什么会这样。 以下是代码段：

func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    ...
    case "addExpense"?:
            if (activeTextField[0].isFirstResponder) {
                if aRR_expenseCategory.count == 0 {
                    ifArrayIsEmpty(forTextField: "category")
                    return 0
                } else {
                    return aRR_expenseCategory.count
                }
            } else if (activeTextField[1].isFirstResponder) {
                if aRR_expenseSubCategory.count == 0 {
                    ifArrayIsEmpty(forTextField: "subCategory")
                    return 0
                } else {
                    return aRR_expenseSubCategory.count
                }
            } else if (activeTextField[4].isFirstResponder) {
                return _aRR_debitedFrom.count
            } else {
                return 0
            }
    ...
}



fileprivate func ifArrayIsEmpty(forTextField tfString: String) {
        // Show Alert
    }

Answer 1

您可以在UITextField的委托方法中执行此操作，即didBeginEditing。

在didBeginEditing内部，重新加载pickerView并检查数据源并显示警报。