UWP TimePicker MVVM

Question

我在将TimePicker的时间属性输入到ViewModel.The方法中的ViewModel中遇到问题

TimePickerTimeSelected()

调用，但在更新时间属性之前调用。

private DateTimeOffset _datePickerValue;
public DateTimeOffset datePickerValue
 {
     get => _datePickerValue;
     set => SetProperty(ref _datePickerValue, value);
 }

这是XAML

<TimePicker
     Name="timePicker"
     Time="{x:Bind viewModel.timePickerValue,Mode=TwoWay}"
     TimeChanged="{x:Bind viewModel.TimePickerTimeSelected,Mode=TwoWay}">

我想用控件中选择它的时间进行一些处理，但是方法在timePickerValue是updated.How之前被调用，我得到新的时间了吗？ViewModel方法：

  public void TimePickerTimeSelected()
  {

  }

Answer 1

在Xaml中，您将Mode=TwoWay设置为无效的TimeChanged事件，因为TmeChange是一个事件，而不是DependencyProperty。

为了达到预期的输出，请参考以下代码：

Xaml：

<TimePicker
   Name="timePicker"
   Time="{x:Bind ViewModel.TimePickerValue, Mode=TwoWay}"
   TimeChanged="{x:Bind ViewModel.TestTimeChangedEvent}"/>

ViewModel：

  private TimeSpan _timePickerValue;
  public TimeSpan TimePickerValue
  {
     get { return _timePickerValue; }
     set { _timePickerValue = value;}
  }

  public void TestTimeChangedEvent(object sender, TimePickerValueChangedEventArgs e)
  {
     TimePickerValue = e.NewTime;
  }

编辑

由于您不希望在您的TimePickerValueChangedEventArgs中使用ViewModel，所以您必须创建一个自定义行为才能在VM中获得所选的时间。

XAML：

 <TimePicker
     Name="timePicker">
    <Interactivity:Interaction.Behaviors>
       <behaviors:TimeChangedEventBehavior/>
    </Interactivity:Interaction.Behaviors>
 </TimePicker>

行为：

  public sealed class TimeChangedEventBehavior : DependencyObject, IBehavior
    {
        public DependencyObject AssociatedObject { get; private set; }

        public void Attach(DependencyObject associatedObject)
        {
            if (!(associatedObject is TimePicker tp))
            {
                throw new ArgumentException("Error Associating Object");
            }

            this.AssociatedObject = associatedObject;

            tp.TimeChanged += OnTimeChanged;
        }

        private void OnTimeChanged(object sender, TimePickerValueChangedEventArgs e)
        {
            var timePicker = (sender as TimePicker);
            var mainVM = (timePicker.DataContext as MainViewModel);
            mainVM.OnTimePickerTimeSelected(timePicker.Time);
        }

        public void Detach()
        {
            if (this.AssociatedObject is TimePicker tp)
            {
                tp.TimeChanged -= this.OnTimeChanged;
            }
        }
    }

ViewModel：

 public void OnTimePickerTimeSelected(TimeSpan selectedTime)
 {
     // Your Logic       
 }