I have a Model class Person, which has some string properties. In the UI, there are some Entry fields that, when a button is pressed, does the following in a ViewModel class:

我有一个Model类Person，它有一些字符串属性。在用户界面中，当按下按钮时，在ViewModel类中有一些输入字段执行以下操作：

• creates a Person object with the values from the fields populating the object's properties

  使用填充对象属性的字段中的值创建Person对象

  
  



• adds the Person object to an ObservableList<Person> , which itself is created in the constructor of the ViewModel class

  将Person对象添加到ObservableList ，该对象本身是在ViewModel类的构造函数中创建的

  
  

I then try to display some of the Person object's properties in a CollectionView list. A list of the string values. I'd like it to look something like this:

然后，我尝试在CollectionView列表中显示Person对象的一些属性。字符串值的列表。我希望它看起来像这样：

I know that both the Person object is being created and the ObservableList<Person> list is being populated, as I can see the values when I step through the code.

我知道Person对象正在被创建，ObservableList 列表正在被填充，因为我在单步执行代码时可以看到这些值。

Person.cs

Person.cs

namespace BindingDemo.Model
{
    public partial class Person : ObservableObject
    {
        #region PersonObjectProperties
        [ObservableProperty]
        private string firstName;
        [ObservableProperty]
        private string lastName;
        [ObservableProperty]
        private string email;
        [ObservableProperty]
        private string password;
        #endregion PersonObjectProperties



        public void ClearFields()
        {
            FirstName = string.Empty;
            LastName = string.Empty;
            Email = string.Empty;
            Password = string.Empty;
        }
    }
}

ViewModel class:

ViewModel类：

using BindingDemo.Model;

namespace BindingDemo.ViewModel
{
    public partial class MainPageViewModel : ObservableObject
    {
        public Person Person { get; } = new Person();

        [ObservableProperty]
        private ObservableCollection<Person> persons;
        
        public MainPageViewModel()
        {
            persons = new ObservableCollection<Person>();
        }

        [RelayCommand]
        private void AddPersonToListAndDb()
        {
            // every field must have a value
            if (string.IsNullOrWhiteSpace(Person.FirstName) || 
                string.IsNullOrWhiteSpace(Person.LastName) || 
                string.IsNullOrWhiteSpace(Person.Email) || 
                string.IsNullOrWhiteSpace(Person.Password))
                return;

            // add the Person object to the list of Person objects
            Persons.Add(Person);

            // clear the fields in the UI so the user can add another person
            Person.ClearFields();
           
            // add the Person object to a database
        }
    }
}

View class:

查看类：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="BindingDemo.MainPage"
             Title="Create Person"
             xmlns:viewmodel="clr-namespace:BindingDemo.ViewModel"
             x:DataType="viewmodel:MainPageViewModel">

      <Grid RowDefinitions="Auto, Auto, Auto, Auto, Auto,*"
            Margin="10">
            <Entry Grid.Row ="0" 
                   Placeholder="Enter your first name"
                   PlaceholderColor="DarkGoldenrod"
                   FontAttributes="Bold"
                   Text="{Binding Person.FirstName}" />

            <Entry Grid.Row="1"
                   Placeholder="Enter your last name"
                   PlaceholderColor="DarkGoldenrod"
                   FontAttributes="Bold"
                   Text="{Binding Person.LastName}" />

            <Entry Grid.Row="2"
                   Placeholder="Enter your email address"
                   PlaceholderColor="DarkGoldenrod"
                   FontAttributes="Bold"
                   Text="{Binding Person.Email}" />

            <Entry Grid.Row="3"                                   
                   Placeholder="Enter your password"
                   PlaceholderColor="DarkGoldenrod"
                   FontAttributes="Bold"
                   IsPassword="True"
                   Text="{Binding Person.Password}" />

            <Button Grid.Row="4"  
                    Margin="10"
                    Text="Add to Database"
                    FontAttributes="Bold"
                    HorizontalOptions="Center"
                    Command="{Binding AddPersonToListAndDbCommand}"/>



            <CollectionView Grid.Row="5" 
                            ItemsSource="{Binding Persons}">
                  <CollectionView.ItemTemplate>
                        <DataTemplate>
                              <StackLayout Margin="5">
                                    <HorizontalStackLayout>
                                          <Label Text="First name:" />
                                          <Label Text="{Binding Person.FirstName}" />
                                    </HorizontalStackLayout>
                                    <HorizontalStackLayout>
                                          <Label Text="Last name:" />
                                          <Label Text="{Binding Person.LastName}" />
                                    </HorizontalStackLayout>
                                    <HorizontalStackLayout>
                                          <Label Text="Email address: " />
                                          <Label Text="{Binding Person.Email}" />
                                    </HorizontalStackLayout>
                              </StackLayout>
                        </DataTemplate>
                  </CollectionView.ItemTemplate>
            </CollectionView>
      </Grid>
</ContentPage>

The problem is most likely in the Binding, but I don't know what else to try.

问题很可能出在绑定上，但我不知道还能尝试什么。

When I'm debugging, I hover my mouse over over the Text={Binding Person.FirstName} to see the value of Person.FirstName. Well, if I hover over Person I can drill down into the object and all the correct values are there, but when I hover over FirstName, it gives the error children could not be evaluated.

当我调试时，我将鼠标悬停在文本={BindingPerson.FirstName}上，以查看Person.FirstName的值。嗯，如果我将鼠标悬停在Person上，我可以向下钻取到对象，所有正确的值都在那里，但当我将鼠标悬停在FirstName上时，它会给出错误：无法评估子代。

To illustrate that the list of Person objects is being created, here is an image of a watch, after I've created a few objects and put them into the list:

为了说明正在创建Person对象列表，在我创建了几个对象并将它们放入列表之后，下面是一个手表的图像：

EDIT: this is my MainPage.xaml.cs code:

编辑：这是我的MainPage.xaml.cs代码：

    using BindingDemo.ViewModel;

namespace BindingDemo
{
    public partial class MainPage : ContentPage
    {
        public MainPage(MainPageViewModel mainPageViewModel)
        {
            InitializeComponent();
            BindingContext = mainPageViewModel;
        }
    }
}

because your ItemsSource is an IEnumerable<Person>, each row of the CollectionView has a BindingContext of the current Person object

因为您的ItemsSource是IEumable ，所以CollectionView的每一行都有当前Person对象的BindingContext

that means the binding expression in the DataTemplate would be relative to a Person object, ie

这意味着数据模板中的绑定表达式将相对于Person对象，即

Text="{Binding FirstName}"

however, because you are using compiled bindings, you also need to specify the DataType

但是，由于您使用的是已编译的绑定，因此还需要指定dataType

<DataTemplate x:DataType="model:Person">

you will also need to add an xmlns declaration for model

您还需要为模型添加一个xmlns声明