xaml - 加载 ViewModel 时绑定(bind) Picker 和 DatePicker 的默认值

Question

我想在 DatePicker 上设置选定日期和 Picker 上的选定项目何时开启ViewModel类加载。我是怎么做的

public override void OnNavigatedTo(INavigationParameters parameters)
{
    base.OnNavigatedTo(parameters);
    var objL = parameters.GetValue<LeaveManagement>("LeaveItem");
    SelectedFromDate = objL.StartDate;
    SelectedToDate = objL.EndDate;
    SelectedLeaveType = new SpinnerBind { Name = objL.LeaveTypeCD, Value = objL.LeaveTypeId };           
}

private DateTime? _selectedFromDate;
public DateTime? SelectedFromDate
{
    get { return _selectedFromDate; }
    set { _selectedFromDate = value; }
}
private DateTime? _selectedToDate;
public DateTime? SelectedToDate
{
    get { return _selectedToDate; }
    set { _selectedToDate = value; }
}

private ObservableCollection<SpinnerBind> _leaveType;
public ObservableCollection<SpinnerBind> LeaveType
{
    get { return _leaveType; }
    set
    {
        SetProperty(ref _leaveType, value);
    }
}
private SpinnerBind _selectedLeaveType;
public SpinnerBind SelectedLeaveType
{
    get { return _selectedLeaveType; }
    set
    {
        SetProperty(ref _selectedLeaveType, value);
    }
}

这是我的 XAMl

<RelativeLayout>
    <DatePicker Format="dd/MM/yyyy"   Date="{Binding SelectedFromDate}"/>

    <DatePicker  Format="dd/MM/yyyy" Date="{Binding SelectedToDate}"/>

    <Picker SelectedItem="{Binding SelectedLeaveType, Mode=TwoWay}" ItemsSource="{Binding LeaveType,Mode=TwoWay}"
            TitleColor="Black" TextColor="Black" Title="--Select--"/>
</RelativeLayout>

但未设置所有值 Startdate、Enddate 和 SelectedLeaveType。然而Picker与 LeaveType 绑定(bind)我该如何解决这个问题？

Answer 1

当 View 模型的某个属性发生变化时，它需要引发 INotifyPropertyChanged.PropertyChanged更新绑定(bind)。

Prism 提供 BindableBase View 模型的基类，具有 SetProperty通常用于更新支持字段并在需要时引发事件的方法。

也就是说，你想要这样的东西

public DateTime? SelectedFromDate
{
    get { return _selectedFromDate; }
    set { SetProperty( ref _selectedFromDate, value ); }
}

编辑:绑定(bind)Picker使用默认选中项，初始化 SelectedLeaveType来自 Source .