Xamarin Forms 在绑定到 Enrty 的文本属性时冻结

Question

Not sure how this is happening but two of my Entry elements will freeze the entire application when their Text is bound. They look essentially the same as everywhere else Entries are used within the app, the only difference being, when included the application freezes. It just doesn't make sense why these break but the others, which are setup exactly the same, don't. Any help, advice, or suggestions are appreciated!

Offending entries:

 <Label Margin="3">Professor Phone</Label>
 <Entry Text="{Binding ProfessorPhone}" Placeholder="Professor Email" Margin="3" />
 <Label Margin="3">Professor Email</Label>
 <Entry Text="{Binding ProfessorEmail}" Placeholder="Professor Phone" />

View:

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="TermManager.Views.CourseDetailView">
<ContentPage.ToolbarItems>
    <ToolbarItem Text="Update" />
</ContentPage.ToolbarItems>
<ContentPage.Content>
    <ScrollView>
        <StackLayout>
            <Label Text="Course Details" VerticalOptions="Center" HorizontalTextAlignment="Center" IsVisible="true" FontSize="Large" FontAttributes="Bold" TextColor="DarkBlue" Margin="10" />
            <Label Margin="3">Course Title</Label>
            <Entry Text="{Binding CourseTitle}" Placeholder="Course Title" Margin="3" />
            <Label Margin="3">Start Date</Label>
            <DatePicker Date="{Binding StartCourseDate}" Margin="3" />
            <Label Margin="3">End Date</Label>
            <DatePicker Date="{Binding EndCourseDate}" Margin="3" />
            <Picker SelectedItem="{Binding CourseStatus}" Title="Course Status" Margin="3" TitleColor="DarkBlue">
                <Picker.ItemsSource>
                    <x:Array Type="{x:Type x:String}">
                        <x:String>in progress</x:String>
                        <x:String>completed</x:String>
                        <x:String>dropped</x:String>
                        <x:String>plan to take</x:String>
                    </x:Array>
                </Picker.ItemsSource>
            </Picker>
            <Label Margin="3">Professor Name</Label>
            <Entry Text="{Binding ProfessorName}" Placeholder="Professor's Name" Margin="3" />
            <Label Margin="3">Professor Email</Label>
            <Entry Text="{Binding ProfessorPhone}" Placeholder="Professor Email" Margin="3" />
            <Label Margin="3">Professor Phone</Label>
            <Entry Text="{Binding ProfessorEmail}" Placeholder="Professor Phone" />
        </StackLayout>
    </ScrollView>
</ContentPage.Content>

Code Behind:

using System;
using System.Collections.Generic;
using TermManager.Models;
using TermManager.ViewModels;
using Xamarin.Forms;

namespace TermManager.Views
{
    public partial class CourseDetailView : ContentPage
    {
        protected Course Course = new Course();

        public CourseDetailView(Course course)
        {
            InitializeComponent();
            BindingContext = new CourseDetailViewModel(Navigation, course);
        }
    }
}

ViewModel:

using System;
using Xamarin.Forms;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using TermManager.Models;

namespace TermManager.ViewModels
{
    public class CourseDetailViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        public Command UpdateCourse { get; private set; }
        protected readonly INavigation Nav;

        protected int _courseId;
        protected int _termId;
        protected string _courseTitle;
        protected DateTime _startCourseDate;
        protected DateTime _endCourseDate;
        protected string _courseStatus;
        protected string _name;
        protected string _email;
        protected string _phone;

        public int CourseId
        {
            get => _courseId;
            set
            {
                _courseId = value;
                OnPropertyChanged();
            }
        }
        public int TermId
        {
            get => _termId;
            set
            {
                _termId = value;
                OnPropertyChanged();
            }
        }
        public string CourseTitle
        {
            get => _courseTitle;
            set
            {
                _courseTitle = value;
                OnPropertyChanged();
            }
        }
        public DateTime StartCourseDate
        {
            get => _startCourseDate;
            set
            {
                _startCourseDate = value;
                OnPropertyChanged();
            }
        }
        public DateTime EndCourseDate
        {
            get => _endCourseDate;
            set
            {
                _endCourseDate = value;
                OnPropertyChanged();
            }
        }
        public string CourseStatus
        {
             get => _courseStatus;
            set
            {
                _courseStatus = value;
                OnPropertyChanged();
            }
        }
        public string ProfessorName
        {
            get => _name;
            set
            {
                _name = value;
                OnPropertyChanged();
            }
        }
        public string ProfessorEmail
        {   
            get => ProfessorEmail;
            set
            {
                _email = value;
                OnPropertyChanged();
            }
        }
        public string ProfessorPhone
        {
            get => ProfessorPhone;
            set
            {
                _phone = value;
                OnPropertyChanged();
            }
        }

        public CourseDetailViewModel(INavigation nav, Course course = null)
        {
            Nav = nav;

            if (course != null)
            {
                _courseId = course.CourseId;
                _termId = course.TermId;
                _courseTitle = course.CourseTitle;
                _courseStatus = course.CourseStatus;
                _startCourseDate = course.StartCourseDate;
                _endCourseDate = course.EndCourseDate;
                _name = course.ProfessorName;
                _email = course.ProfessorEmail;
                _phone = course.ProfessorPhone;
            }
        }

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

Answer 1

The problem is in your getters for the ProfessorPhone and ProfessorEmail properties, there you have to return the protected fields, but instead you are returning the property itself, which causes an infinite loop!

Change your code as follows:

public string ProfessorEmail
{   
    get => _email;
    set
    {
        _email = value;
        OnPropertyChanged();
    }
}
public string ProfessorPhone
{
    get => _phone;
    set
    {
        _phone = value;
        OnPropertyChanged();
    }
}