在XAML中而不是在代码后面设置DataContext

Question

我已经阅读过其他文章，代替在代码中指定DataContext，可以在XAML中指定它。

我有一个ObservableCollection和宣布，以我的主类的构造函数填充，我还设置了DataContext的：

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，在我的应用效果很好。

但是，如果我删除“DataContext = this;”从构造函数中取而代之在我的应用程序的Window元素中设置DataContext

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

我得不到数据。

这是我设置DataContext的我从代码中删除它后，后面的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> 

在我在做什么错误任何帮助将不胜感激。

谢谢！

Answer 1

你需要设置你的源之前调用的InitializeComponent

编辑：其实你只需要在InitializeComponent之前初始化它，因为这是它实现INotifyCollectionChanged一个ObservableCollection，所以如果你修改集合，网格会更新了更改。

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的答案有效。或者，您可以实施INotifyPropertyChanged，以便在设置PersonList时通知XAML。

ObservableCollection只在收集变更项目时通知。如果您想在为集合（例如PersonList = new ObservableCollection<Person>()）分配新值时通知您，则需要执行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. 
    } 
}