即使未设置绑定属性，DatePicker 也会选择选择

Question

我收到了我的DatePicker。我检查新的发布日期是否是equal or greater 而不是SelectedOrder.TargetDate.Date。 检查本身很好，如果coindition 不匹配，则不允许检查，但是user 在calendar 上选择的内容仍保留在calendar 中。为什么calendar 设置用户的选择，即使SelectedTargetDate 没有改变？

<DatePicker Date="{Binding SelectedTargetDate, Mode=TwoWay}"/>


public DateTime SelectedTargetDate
        {
            get =>  _selectedTargetDate;
            set
            {
                if (SelectedOrder == null) return;      //on program run first time it's null
                if (value.Date < SelectedOrder.TargetDate.Date)
                    _pageService.DisplayAlert("Ostrzeżenie", "New date cannot be older than TargetDate", "ok", "cancel");
                else
                    SetValue(ref _selectedTargetDate, value);
            }
        }

Answer 1

不知道我对你的理解是否正确，如果条件不满足，要不要保留SelectedOrder.TargetDate？

如果是，您可以让您的模型实现INotifyPropertyChanged 并进行如下更改：

public class YourModel: INotifyPropertyChanged
{
    ...
    public event PropertyChangedEventHandler PropertyChanged;

    public DateTime SelectedTargetDate
    {
        get => _selectedTargetDate;
        set
        {
            if (SelectedOrder == null) return;      //on program run first time it's null
            if (value.Date < SelectedOrder.Date)
            {
                _pageService.DisplayAlert("Ostrzeżenie", "New date cannot be older than TargetDate", "ok", "cancel");
            }
            else
            {
                _selectedTargetDate = value;
            }
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("SelectedTargetDate"));
        }
    }

    
}