ios - UIPickerView pickerView :titleForRow:rowforComponent method not called

Question

我的 Storyboard中有一个 UIPickerView。包含它的 UIViewController 设置了接口(interface)声明

@interface ContactDetail : UIViewController <ABPeoplePickerNavigationControllerDelegate, UIPickerViewDataSource, UIPickerViewDelegate,UIAlertViewDelegate, UITextFieldDelegate>

on view Load, pickerview委托(delegate)集

pickerView_RelationshipType.dataSource=self;
pickerView_RelationshipType.delegate = self;
pickerView_RelationshipType.showsSelectionIndicator = YES;

除那两个之外，所有 UIPickerView 数据源和委托(delegate)方法都被触发

pickerView:titleForRow:rowforComponent
and
pickerView:viewForRow:forComponent:reusingView

调用下面的，没问题

    - (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
    - (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
    - (void)pickerView:(UIPickerView *)pickerView didSelectRow: (NSInteger)row inComponent:(NSInteger)component
    - (CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component

Answer 1

numberOfComponentsInPickerView 中有什么？

如果您的 numberOfRows 返回 0，那么您的委托(delegate)方法将永远不会被调用 - 如果选择器认为没有任何行要显示，则它不会询问行的标题。