不兼容的指针类型分配给＆＃39; UIDatePicker *＆＃39;来自＆＃39; UIPopoverController *＆＃39;

Question

我正在尝试调整此帖子中的第一个答案：How can I show a UIDatePicker inside a Popover on iPad using StoryBoard?

这是我改编的代码（datePicker在viewDidLoad中初始化）：

CGRect pickerFrame = CGRectMake(0, 0, 320, 216);
datePicker = [[UIDatePicker alloc] initWithFrame:pickerFrame];
datePicker.datePickerMode = UIDatePickerModeDate;

- (IBAction)btnSurveyDate:(UIButton *)sender
{
    //Build custom popover view.
    UIView *v = [[UIView alloc] init];
    [v addSubview:datePicker];

    UIViewController *popoverContent = [[UIViewController alloc] init];
    popoverContent.view = v;

    //Resize the popover view shown in the current view to the view's size.
    popoverContent.preferredContentSize = CGSizeMake(320, 216);

    //Create a popover controller with my DatePickerViewController in it.
    UIPopoverController *poDate = [[UIPopoverController alloc] initWithContentViewController:popoverContent];

    //Set the delegate to self to receive the data of the DatePicker in the popover.
    poDate.delegate = self;

    //Present the popover.
    [poDate presentPopoverFromRect:self.txtSurveyDate.frame
                            inView:self.view
          permittedArrowDirections:UIPopoverArrowDirectionAny
                          animated:YES];

    datePicker = poDate;
}

- (void)popoverControllerDidDismissPopover:(UIPopoverController *)popoverController
{
    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setDateFormat:@"dd/MM/yyyy"];        
    NSString *dt = [df stringFromDate:datePicker.date];
    self.txtSurveyDate.text = [NSString stringWithFormat:@"%@",dt];
}

然而，有两个问题。首先，我在最后一行收到编译器警告：

datePicker = poDate;

错误是：

Incompatible pointer types assigning to 'UIDatePicker *' from 'UIPopoverController *' 

其次，应用程序在解除弹出窗口时崩溃，错误为：

unrecognized selector sent to instance

应用程序在popoverControllerDidDismissPopover方法中的此行停止：

NSString *dt = [df stringFromDate:datePicker.date];

Answer 1

poDate是UIPopoverController的实例，而datePicker是变量类型UIDatePicker，这就是您在该行上收到警告的原因。

所以在这一行（程序崩溃的地方）：

NSString *dt = [df stringFromDate:datePicker.date];

date消息被发送到datePicker，UIPopoverController实际上是date的实例。 Popover控制器没有{{1}}方法，因此程序崩溃。