Xamarin Forms 渲染器不响应事件更改

Question

我对 Xamarin 表单和自定义渲染器部分还很陌生。我已经为日期选择器编写了一个自定义渲染器，并且在 xamarin 表单中使用了相同的渲染器。

下面是我的 XAML 、ViewModel 和渲染器类的代码。

XAML :

<flightControls:CustomDatePicker x:Name="FromDatePicker" Date="{Binding FromDate}" >
       <flightControls:CustomDatePicker.Behaviors>
              <behaviour:CommandBehavior EventName="DateSelected" Command="{Binding FromDateSelectedCommand}" CommandParameter="{Binding Source={x:Reference FromDatePicker}}" />
       </flightControls:CustomDatePicker.Behaviors>
</flightControls:CustomDatePicker>

查看模型

起始日期属性:

    private DateTime _fromDate;
    public DateTime FromDate
    {
        get
        {
            return (_fromDate == default(DateTime)) ? DateTime.Now : _fromDate;
        }
        set
        {

            _fromDate = (value == default(DateTime)) ? DateTime.Now : value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("FromDate"));
        }
    }

FromDateSelectedCommand 命令：

public ICommand FromDateSelectedCommand { get; set; }
FromDateSelectedCommand = new DelegateCommand<object>(FromDateSelected);
private void FromDateSelected(object selectedDate)
{
    FromDate = ((DatePicker)selectedDate).Date;
}

自定义日期选择器Class:

public class CustomDatePicker : DatePicker
{

}

CustomDatePickerRenderer UWP 渲染器：

public class CustomDatePickerRenderer:ViewRenderer<Xamarin.Forms.DatePicker,Windows.UI.Xaml.Controls.CalendarDatePicker>
{
    CalendarDatePicker datePicker = new CalendarDatePicker();

    /// <summary>
    /// OnElement Changed method to get the Native DatePicker element
    /// </summary>
    /// <param name="e"></param>
    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.DatePicker> e)
    {           

        base.OnElementChanged(e);
        if (e.NewElement != null)
        {
            datePicker.PlaceholderText = "Select Date";
            datePicker.Date = e.NewElement.Date;
            datePicker.PlaceholderText = "dd-mm-yyyy";

            datePicker.DateChanged += DatePicker_DateChanged;

            SetNativeControl(datePicker);
        }
    }

    private void DatePicker_DateChanged(CalendarDatePicker sender, CalendarDatePickerDateChangedEventArgs args)
    {


    }
}

如何从渲染器获取更新的日期更改值并将其分配回我的视图模型的 FromDate 属性？因为 DateChanged 命令根本没有被调用。我怀疑必须通过返回一个值来对渲染器的日期更改事件做一些事情。

现在 FromDate 属性始终具有默认值 DateTime.Now 并且在选择器中更改日期时不会更新。

如有任何帮助，我们将不胜感激。

Answer 1

找到解决方案。如下设置值确实触发了 DateChanged 事件绑定到的命令。在我的 CustomDatePickerRenderer DateChanged 事件中，我不得不写下一行

private void DatePicker_DateChanged(CalendarDatePicker sender, CalendarDatePickerDateChangedEventArgs args)
{    
    // This line triggered the DateChanged event in view model.
    Element.Date = args.NewDate.Value.Date;
}

Xamarin Forms 渲染器不响应事件更改

Xamarin Forms renderer not responding to event change

custom-renderer

xamarin

xamarin.forms

uwp

xamarin.uwp