可观察集合列表框中没有更新

Question

我有一个绑定到 Observablecollection 的 Silverlight 列表框，它显示得很好（第一次），但是当我尝试通过后面的代码更新它时，更改不会反映在 UI 中。我用过MVVM模式。请查看视图和视图模型。

<UserControl x:Class="GridOperations.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:GridOperations.ViewModel"
    mc:Ignorable="d"
    d:DesignHeight="700" d:DesignWidth="700">
    <UserControl.DataContext>
        <local:ShowUserListViewModel/>
    </UserControl.DataContext>
    <UserControl.Resources>
        <local:ShowUserListViewModel x:Key="viewModelKey"/>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">

        <ListBox VerticalAlignment="Top" Margin="0,20,0,0" x:Name="lstBox" ItemsSource="{Binding UserList}" Width="700" Height="150" Background="AliceBlue">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="300"/>
                            <ColumnDefinition Width="100"/>
                            <ColumnDefinition Width="100"/>
                            <ColumnDefinition Width="100"/>
                        </Grid.ColumnDefinitions>
                        <TextBlock Margin="30,0,0,0" Text="{Binding UserId}" HorizontalAlignment="Left"/>
                        <TextBlock Margin="30,0,0,0" Text="{Binding Path=UserName, Mode=TwoWay}" Grid.Column="1" HorizontalAlignment="Left"/>
                        <Button Margin="30,0,0,0" Grid.Column="2" Content="Edit" Height="20" HorizontalAlignment="Left" Command="{Binding Source={StaticResource viewModelKey}, Path=UpdateUserCommand}" />
                        <Button Margin="10,0,0,0" Grid.Column="3" Content="Del" Height="20" HorizontalAlignment="Left" />
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

    </Grid>
</UserControl>


    public class ShowUserListViewModel : INotifyPropertyChanged
        {
            public ShowUserListViewModel()
            {
                mUserList = new ObservableCollection<User>();
                mUserList.Add(new User() { UserId = Guid.NewGuid().ToString(), UserName = "testuser1", IsAdmin = true });
                mUserList.Add(new User() { UserId = Guid.NewGuid().ToString(), UserName = "testuser2", IsAdmin = true });

                this.UpdateUserCommand = new DelegateCommand(this.UpdateUser);

            }

            public ICommand UpdateUserCommand { get; private set; }

            private ObservableCollection<User> mUserList;
            public ObservableCollection<User> UserList
            {
                get
                {
                    return mUserList;
                }
            }

            public event PropertyChangedEventHandler PropertyChanged;

            private void UpdateUser()
            {
                this.UserList.Add(new User() { UserId = Guid.NewGuid().ToString(), UserName = "test", IsAdmin = false });            
            }
        }

Answer 1

首先，您应该避免将集合属性设置为可写。 IE，替换此代码：

    private ObservableCollection<User> mUsers = new ObservableCollection<User>();
    public ObservableCollection<User> Users
    {
        get
        {
            return mUsers;
        }
        set
        {
            mUsers = value;
            RaisePropertyChangedEvent("Users");
        }
    }

通过此代码：

    private ObservableCollection<User> mUsers = new ObservableCollection<User>();
    public ObservableCollection<User> Users
    {
        get
        {
            return mUsers;
        }

    }

然后，当您将项目添加到集合中时，您不必告诉集合已更改（集合属性本身没有更改），但这是该集合的责任集合本身（通过 INotifyCollectionChanged）：

因此，“onclick”方法可以简单地像这样：

 private void OnClick(User userInstanceToEdit)
    {
        this.Users.Add(new User() { UserId = Guid.NewGuid().ToString(), UserName = "test", IsAdmin = false });         

    }

最后，我将用此方法替换 ListBox.ItemsSource 声明，因为不需要两种方法：

 <ListBox x:Name="lstBox" ItemsSource="{Binding Users}" 

Answer 2

从这篇文章中得到了提示 Stackoverflow

基本上我需要将 Datacontext 与 Listbox 控件一起使用（即使在 UserControl 级别设置 Datacontext 之后）。唯一需要更改的行是：

<ListBox x:Name="lstBox" ItemsSource="{Binding Users}" DataContext="{StaticResource viewModelKey}"  Width="750" Background="AliceBlue">