Xamarin Forms 在绑定到 Enrty 的文本属性时冻结

Question

不知道这是怎么发生的，但是我的两个 Entry 元素会在它们的 Text 被绑定时冻结整个应用程序。 它们看起来与在应用程序中使用的任何其他条目基本相同，唯一的区别是，当包含应用程序时，应用程序会冻结。 为什么这些会中断是没有意义的，但其他设置完全相同的却不会。 任何帮助，建议或建议表示赞赏！

违规条目：

 <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" />

看法：

<?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>

代码背后：

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);
        }
    }
}

视图模型：

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

问题出在ProfessorPhone和ProfessorEmail属性的getter 中，您必须返回受保护的字段，而是返回属性本身，这会导致无限循环！

更改您的代码如下：

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