C# 更改ObservableCollection后ListView未更新

我有一个列表视图，我一得到数据就更新它。如果我在ViewModel的构造函数中向observableCollection添加项，则ListView会得到更新，但如果我在收到回调后以某种方法进行了添加，则ListView不会得到更新。

我在Stackoverflow上花了很多时间，我知道有很多相关的问题，但我找不到答案。困扰我的是，如果我在构造函数中添加值时它起作用，那么为什么我在某个方法中添加值时它不起作用

• 我正在使用ObservableCollection
• 设置数据上下文
• 在XAML中将ObservableCollection绑定到ListView

这是XAML代码

<UserControl x:Class="WFP_Illustrated.UserControls.WeatherForcastControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300"
         >
<UserControl.Resources>
    <Style TargetType="TextBlock" x:Key="TextStyle">
        <Setter Property="FontFamily" Value="Adobe Caslon Pro"/>
        <Setter Property="FontSize" Value="18"/>
        <Setter Property="MinWidth" Value="60"/>
    </Style>
    <DataTemplate x:Key="ForcastTemplate">
        <Border BorderBrush="Aqua" BorderThickness="1" Padding="5" Margin="5">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                </Grid.ColumnDefinitions>

                <TextBlock Grid.Row="0" Grid.ColumnSpan="2" Text="{Binding Path= Day}" Style="{StaticResource TextStyle}"/>
                <TextBlock Grid.Row="1" Grid.Column="0" Text="{Binding Path= Condition}"   Style="{StaticResource TextStyle}"/>
                <Image Grid.Row="1" Grid.Column="1" />
                <TextBlock Grid.Row="2" Grid.Column="0" Text="{Binding Path= Low}"  Style="{StaticResource TextStyle}"/>
                <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding Path= High}"  Style="{StaticResource TextStyle}"/>
            </Grid>
        </Border>
    </DataTemplate>
</UserControl.Resources>
<Grid>
    <ListView Name="ForcastList"
             ItemTemplate="{StaticResource ForcastTemplate}"
             ItemsSource="{Binding ForcastList}"
             Background="SlateGray"
             >

    </ListView>
</Grid>

  private ObservableCollection<ForcastInfo> _forcastList;
    public ObservableCollection<ForcastInfo> ForcastList
    {
        get { return _forcastList; }
        //set
        //{
        //    _forcastList = value;
        //    OnPropertyChanged("ForcastList");
        //}
    }

    public WeatherForcastViewModel()
    {
        //If this is uncommented , I will see values in ListView
        //ForcastInfo forcast = new ForcastInfo();
        //forcast.Condition = "clear";
        //forcast.Day = "Sunday";
        //forcast.High = "70";
        //forcast.Low = "50";
        //_forcastList = new ObservableCollection<ForcastInfo>();
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);

        //Callback from MainView ,forcast data is available
        Messenger.Default.Register<GoToForcast>
       (
            this, (action) => MessageFromMain(action)
       );
    }

    private void MessageFromMain(GoToForcast message)
    {
        //This should work but its not working
        ForcastInfo forcast = new ForcastInfo();
        forcast.Condition = "clear";
        forcast.Day = "Sunday";
        forcast.High = "70";
        forcast.Low = "50";
        _forcastList = new ObservableCollection<ForcastInfo>();
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);

        //ForcastList = message.ForcastList;
    }

这是ModelView代码

<UserControl x:Class="WFP_Illustrated.UserControls.WeatherForcastControl"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300"
         >
<UserControl.Resources>
    <Style TargetType="TextBlock" x:Key="TextStyle">
        <Setter Property="FontFamily" Value="Adobe Caslon Pro"/>
        <Setter Property="FontSize" Value="18"/>
        <Setter Property="MinWidth" Value="60"/>
    </Style>
    <DataTemplate x:Key="ForcastTemplate">
        <Border BorderBrush="Aqua" BorderThickness="1" Padding="5" Margin="5">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition/>
                    <RowDefinition/>
                    <RowDefinition/>
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition/>
                    <ColumnDefinition/>
                </Grid.ColumnDefinitions>

                <TextBlock Grid.Row="0" Grid.ColumnSpan="2" Text="{Binding Path= Day}" Style="{StaticResource TextStyle}"/>
                <TextBlock Grid.Row="1" Grid.Column="0" Text="{Binding Path= Condition}"   Style="{StaticResource TextStyle}"/>
                <Image Grid.Row="1" Grid.Column="1" />
                <TextBlock Grid.Row="2" Grid.Column="0" Text="{Binding Path= Low}"  Style="{StaticResource TextStyle}"/>
                <TextBlock Grid.Row="2" Grid.Column="1" Text="{Binding Path= High}"  Style="{StaticResource TextStyle}"/>
            </Grid>
        </Border>
    </DataTemplate>
</UserControl.Resources>
<Grid>
    <ListView Name="ForcastList"
             ItemTemplate="{StaticResource ForcastTemplate}"
             ItemsSource="{Binding ForcastList}"
             Background="SlateGray"
             >

    </ListView>
</Grid>

  private ObservableCollection<ForcastInfo> _forcastList;
    public ObservableCollection<ForcastInfo> ForcastList
    {
        get { return _forcastList; }
        //set
        //{
        //    _forcastList = value;
        //    OnPropertyChanged("ForcastList");
        //}
    }

    public WeatherForcastViewModel()
    {
        //If this is uncommented , I will see values in ListView
        //ForcastInfo forcast = new ForcastInfo();
        //forcast.Condition = "clear";
        //forcast.Day = "Sunday";
        //forcast.High = "70";
        //forcast.Low = "50";
        //_forcastList = new ObservableCollection<ForcastInfo>();
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);
        //ForcastList.Add(forcast);

        //Callback from MainView ,forcast data is available
        Messenger.Default.Register<GoToForcast>
       (
            this, (action) => MessageFromMain(action)
       );
    }

    private void MessageFromMain(GoToForcast message)
    {
        //This should work but its not working
        ForcastInfo forcast = new ForcastInfo();
        forcast.Condition = "clear";
        forcast.Day = "Sunday";
        forcast.High = "70";
        forcast.Low = "50";
        _forcastList = new ObservableCollection<ForcastInfo>();
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);
        ForcastList.Add(forcast);

        //ForcastList = message.ForcastList;
    }

private observeCollection\u forcastList；
公共可观测集合ForcastList
{
获取{return\u forcastList；}
//设置
//{
//_forcastList=值；
//OnPropertyChanged（“ForcastList”）；
//}
}
公共天气ForCastViewModel（）
{
//如果这是未注释的，我将在ListView中看到值
//ForcastInfo forcast=新建ForcastInfo（）；
//forcast.Condition=“clear”；
//forcast.Day=“星期日”；
//预测。高=“70”；
//forcast.Low=“50”；
//_forcastList=新的ObservableCollection（）；
//预测列表。添加（预测）；
//预测列表。添加（预测）；
//预测列表。添加（预测）；
//预测列表。添加（预测）；
//预测列表。添加（预测）；
//预测列表。添加（预测）；
//从MainView回调，预测数据可用
Messenger.Default.Register
(
此（操作）=>MessageFromMain（操作）
);
}
私有void MessageFromMain（GoToForcast消息）
{
//这应该行得通，但行不通
ForcastInfo forcast=新建ForcastInfo（）；
forcast.Condition=“clear”；
forcast.Day=“星期日”；
预测。高=“70”；
forcast.Low=“50”；
_forcastList=新的ObservableCollection（）；
预测列表。添加（预测）；
预测列表。添加（预测）；
预测列表。添加（预测）；
预测列表。添加（预测）；
预测列表。添加（预测）；
预测列表。添加（预测）；
//ForcastList=message.ForcastList；
}

问题在于您正在将_forecastList设置为ObservableCollection的新实例。只要这样做：

public WeatherForcastViewModel()
{

    _forcastList = new ObservableCollection<ForcastInfo>();
    //Callback from MainView ,forcast data is available
    Messenger.Default.Register<GoToForcast>
   (
        this, (action) => MessageFromMain(action)
   );
}


private void MessageFromMain(GoToForcast message)
{
    //This should work but its not working
    ForcastInfo forcast = new ForcastInfo();
    forcast.Condition = "clear";
    forcast.Day = "Sunday";
    forcast.High = "70";
    forcast.Low = "50";
    //_forcastList = new ObservableCollection<ForcastInfo>(); <---- this is messing you up
    ForcastList.Add(forcast);
    ForcastList.Add(forcast);
    ForcastList.Add(forcast);
    ForcastList.Add(forcast);
    ForcastList.Add(forcast);
    ForcastList.Add(forcast);

    //ForcastList = message.ForcastList;
}

public WeatherForcastViewModel（）
{
_forcastList=新的ObservableCollection（）；
//从MainView回调，预测数据可用
Messenger.Default.Register
(
此（操作）=>MessageFromMain（操作）
);
}
私有void MessageFromMain（GoToForcast消息）
{
//这应该行得通，但行不通
ForcastInfo forcast=新建ForcastInfo（）；
forcast.Condition=“clear”；
forcast.Day=“星期日”；
预测。高=“70”；
forcast.Low=“50”；
//_forcastList=new ObservableCollection（）

要么只在setter中的通知中使用属性和注释，要么不可能更改引用，这通常是最好的方法：

private readonly ObservableCollection<ForcastInfo> _forcastList = new ObservableCollection<ForcastInfo>();
public ObservableCollection<ForcastInfo> ForcastList
{
    get { return _forcastList; }
}

private readonly observateCollection\u forcastList=new observateCollection（）；
公共可观测集合ForcastList
{
获取{return\u forcastList；}
}

现在您不能搞乱绑定，因为属性始终指向同一个对象。要使用此设置替换列表，只需调用
Clear（）
并添加新对象。
MessageFromMain做什么？我正在使用MVVM Light，当我有可用的预测条件时，MessageFromMain将被调用。在这个函数中，我只是将从回调中获得的forcastList分配给这个ViewModel的属性。请参阅注释代码。啊，我现在看到了，您正在替换collec更新中的提示。谢谢老兄，我现在觉得自己太蠢了！！哈哈，我花了一段时间才接受ans bcoz，我犯了以下错误
private void MessageFromMain（GoToForcast message）{//我花了很长时间才接受答案bcoz；//我是这样做的//ForcastList=message.ForcastList；//而不是这样做foreach（message.ForcastList中的forcastinfof）{ForcastList.Add（f）；}`