在ObservableCollection被更改后ListView不会更新

问题描述：

我有一个ListView，只要我获取数据就会更新。如果我在ViewModel的构造函数中将项目添加到observableCollection中，ListView会得到更新，但如果我在回调后在某种方法中执行此操作，则不会。在ObservableCollection被更改后ListView不会更新

我花了很多时间在*，我知道有很多相关的问题，但我找不到答案。什么是我的问题是，如果它的工作原理，当我在构造函数中添加值，那么为什么它不工作，如果我在某些方法中添加值。

我使用的ObservableCollection
在XAML

这里设置的DataContext

绑定的ObservableCollection到ListView控件是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>

XAML代码隐藏

public partial class WeatherForcastControl : UserControl 
{ 
    private WeatherForcastViewModel _viewModel; 
    public WeatherForcastControl() 
    { 
     InitializeComponent(); 
     _viewModel = new WeatherForcastViewModel(); 
     this.DataContext = _viewModel; 
    } 
}

这里是模型视图代码

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; 
    }

MessageFromMain做什么？ –

我使用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forcastList分配给我从这个ViewModel的属性中回调。查看评论代码。 –

啊，我现在看到它，你正在更新更新的集合。 –

答

的问题是，你的_forecastList设置为一个ObservableCollection的新实例。只是这样做：

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; 
}

谢谢老兄，我现在觉得很愚蠢！哈哈还我花了一段时间来接受bcoz我正在以下错误
私人无效MessageFromMain（GoToForcast消息） { //了很长时间才接受答案bcoz我这样做 // ForcastList =消息答。 ForcastList; //代替这样做 foreach（for message inFormsList中的ForcastInfo f） ForcastList。加入（F）; } } ' –

我不知道如何在评论中添加代码 –

答

好了，你改变了对象列表属性引用，不通过该方法中的字段设置为一个新的集合告诉它的视图。

要么只使用在通知物业和评论在二传手或只是使它不可能改变的参考，这往往是最好的方法：

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

现在，你就不会搞砸绑定的该属性总是指向同一个对象。要用此设置替换列表，只需调用Clear()并添加新对象。

在ObservableCollection被更改后ListView不会更新

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