在 XAML 中而不是在代码后面设置 DataContext

Question

我在其他帖子中读到，可以在 XAML 中指定，而不是在后面的代码中指定 DataContext。

我在主类的构造函数中声明并填充了一个 ObservableCollection，我还设置了 DataContext：

using System;
using System.Windows;
using System.Collections.ObjectModel;

namespace ItemsControlDemo
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<Person> PersonList { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            PersonList = new ObservableCollection<Person>();

            PersonList.Add(new Person(16, "Abraham", "Lincoln"));
            PersonList.Add(new Person(32, "Franklin", "Roosevelt"));
            PersonList.Add(new Person(35, "John", "Kennedy"));
            PersonList.Add(new Person(2, "John", "Adams"));
            PersonList.Add(new Person(1, "George", "Washington"));
            PersonList.Add(new Person(7, "Andrew", "Jackson"));

            DataContext = this;
        }

        private void Button_Add_Click(object sender, RoutedEventArgs e)
        {
            PersonList.Add(new Person(3, "Thomas", "Jefferson"));
        }

        private void Button_Remove_Click(object sender, RoutedEventArgs e)
        {
            PersonList.Remove(TheDataGrid.SelectedItem as Person);
        }
    }

    public class Person
    {
        public Person() { }

        public Person(int id, string firstName, string lastName)
        {
            ID = id;
            FirstName = firstName;
            LastName = lastName;
        }

        public int ID { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

如果我这样做，我的应用程序一切正常。

但是，如果我删除“DataContext = this;”从构造函数，而是在我的应用程序的 Window 元素中设置 DataContext

        DataContext="{Binding RelativeSource={RelativeSource Self}}"

我没有得到任何数据。

这是我从后面的代码中删除 DataContext 后设置 DataContext 的 XAML：

<Window x:Class="ItemsControlDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:ItemsControlDemo"
        Title="Items Control Demo" Height="350" Width="400"
        WindowStartupLocation="CenterScreen"
        DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <DataGrid Grid.Row="0" Name="TheDataGrid" SelectedValuePath="ID"
                  AutoGenerateColumns="False"
                  AlternatingRowBackground="Bisque"
                  ItemsSource="{Binding PersonList}">
            <DataGrid.Columns>
                <DataGridTextColumn Header="ID"         Binding="{Binding Path=ID}"/>
                <DataGridTextColumn Header="First Name" Binding="{Binding Path=FirstName}"/>
                <DataGridTextColumn Header="Last Name"  Binding="{Binding Path=LastName}"/>
            </DataGrid.Columns>
        </DataGrid>
        <StackPanel Grid.Row="1" Orientation="Horizontal"
                    HorizontalAlignment="Left" VerticalAlignment="Bottom">
            <Button Content="Add Item"    Margin="5" Click="Button_Add_Click"/>
            <Button Content="Remove Item" Margin="5" Click="Button_Remove_Click"/>
        </StackPanel>
    </Grid>
</Window>

对于我做错的事情的任何帮助将不胜感激。

谢谢！

Answer 1

您需要在调用 InitializeComponent

之前设置您的源代码

编辑：实际上你只需要在 InitializeComponent 之前实例化它，因为它是一个 ObservableCollection，它实现了 INotifyCollectionChanged，所以如果你修改集合，你的网格将随着更改而更新。

public MainWindow()
    {
        PersonList = new ObservableCollection<Person>();
        InitializeComponent();
        PersonList.Add(new Person(16, "Abraham", "Lincoln"));
        PersonList.Add(new Person(32, "Franklin", "Roosevelt"));
        PersonList.Add(new Person(35, "John", "Kennedy"));
        PersonList.Add(new Person(2, "John", "Adams"));
        PersonList.Add(new Person(1, "George", "Washington"));
        PersonList.Add(new Person(7, "Andrew", "Jackson"));
    }

Answer 2

216 的回答有效。或者，您可以实现 INotifyPropertyChanged，以便在您设置 PersonList 时通知 XAML。

ObservableCollection 仅在集合中的项目更改时通知。如果您想在为集合分配新值时通知（例如PersonList = new ObservableCollection<Person>()），则需要实现INotifyPropertyChanged。

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private ObservableCollection<Person> personList;

    public ObservableCollection<Person> PersonList
    {
        get { return personList; }
        set
        {
            if (value == personList)
                return;
            personList = value;
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("PersonList"));
        }
    }

    public MainWindow()
    {
        InitializeComponent();

        PersonList = new ObservableCollection<Person>();

        // etc.
    }
}