如何分配Picker和属性

Question

我有ListView（在MainPage上）列出练习，而ExercisePage用于编辑现有或添加新项目。有用。问题是如何使用选择器控件在ExercisePage（而不是muscleGroupEntry）上选择MuscleGroup并在Exercise实例中保存更改？

我尝试使用这里描述的ItemsSource和ItemDisplayBinding属性Bindable picker，但它不起作用。

感谢您的帮助！这是我的代码。

练习课：

    public class Exercise : INotifyPropertyChanged
{
    public enum muscleGroups
    {
        Back,
        Chest
    }

    public string title { get; set; }
    public muscleGroups muscleGroup { get; set; }

    public string Title
    {
        get { return title; }
        set
        {
            if (title != value)
            {
                title = value;
                OnPropertyChanged("Title");
            }
        }
    }

    public muscleGroups MuscleGroup
    {
        get { return muscleGroup; }
        set
        {
            if (muscleGroup != value)
            {
                muscleGroup = value;
                OnPropertyChanged("MuscleGroup");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(string prop = "")
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(prop));
    }

}

ExercisePage.xaml

        <StackLayout>
        <Entry x:Name="titleEntry" Text="{Binding Path=Title}"  />
        <Entry x:Name="muscleGroupEntry" Text="{Binding Path=MuscleGroup}" />
        <Button Text="Save" Clicked="SaveExercise" />
    </StackLayout>

ExercisePage.xaml.cs

    public partial class ExercisePage : ContentPage
{
    bool edited = true;
    public Exercise Exercise { get; set; }

    public ExercisePage (Exercise exercise)
    {
        InitializeComponent ();

        Exercise = exercise;
        if (exercise == null)
        {
            Exercise = new Exercise();
            edited = false;
        }
        this.BindingContext = Exercise;
    }

    async void SaveExercise(object sender, EventArgs e)
    {
        await Navigation.PopAsync();

        if (edited == false)
        {
            NavigationPage navPage = (NavigationPage)Application.Current.MainPage;
            IReadOnlyList<Page> navStack = navPage.Navigation.NavigationStack;
            MainPage homePage = navStack[navPage.Navigation.NavigationStack.Count - 1] as MainPage;

            if (homePage != null)
            {
                homePage.AddExercise(Exercise);
            }
        }
    }

MainPage.xaml中

    <StackLayout>
    <Button Text="Add" Clicked="AddButton_Click" />
    <ListView x:Name="exercisesList" ItemsSource="{Binding}" ItemSelected="OnListViewItemSelected">
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <ViewCell.View>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*" />
                                <ColumnDefinition Width="*" />
                            </Grid.ColumnDefinitions>
                            <Label Text="{Binding Title}" FontSize="Medium" Grid.Column="0" />
                            <Label Text="{Binding MuscleGroup}" FontSize="Medium" Grid.Column="1" />
                        </Grid>
                    </ViewCell.View>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</StackLayout>

MainPage.xaml.cs中

    public partial class MainPage : ContentPage
{
    protected internal ObservableCollection<Exercise> Exercises { get; set; }

    public MainPage()
    {
        InitializeComponent();

        Exercises = new ObservableCollection<Exercise>
        {
            new Exercise {Title="Exercise 1", MuscleGroup = Exercise.muscleGroups.Chest},
            new Exercise {Title="Exercise 2", MuscleGroup = Exercise.muscleGroups.Chest},
            new Exercise {Title="Exercise 3", MuscleGroup = Exercise.muscleGroups.Back},
            new Exercise {Title="Exercise 4", MuscleGroup = Exercise.muscleGroups.Back}
        };
        exercisesList.BindingContext = Exercises;
    }

    private async void OnListViewItemSelected(object sender, SelectedItemChangedEventArgs args)
    {
        Exercise selectedExercise = args.SelectedItem as Exercise;
        if (selectedExercise != null)
        {
            exercisesList.SelectedItem = null;
            await Navigation.PushAsync(new ExercisePage(selectedExercise));
        }
    }

    private async void AddButton_Click(object sender, EventArgs e)
    {
        await Navigation.PushAsync(new ExercisePage(null));
    }

    protected internal void AddExercise(Exercise exercise)
    {
        Exercises.Add(exercise);
    }
}

提前致谢。