ListView在ObservableCollection被改变后没有更新
本文关键字:更新 改变 ObservableCollection ListView | 更新日期: 2023-09-27 18:15:19
我有一个ListView,我一得到数据就更新。如果我在ViewModel的构造函数中将项目添加到observableCollection中,ListView将得到更新,但如果我在获得回调后在某些方法中这样做,则不会更新。
我花了很多时间在Stackoverflow上,我知道有很多相关的问题,但我找不到答案。困扰我的是,如果它的工作,当我在构造函数中添加值,那么为什么它不工作,如果我在一些方法中添加值。- 我正在使用ObservableCollection
- 设置数据背景 在XAML中绑定ObservableCollection到ListView
这里是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代码后面
public partial class WeatherForcastControl : UserControl
{
private WeatherForcastViewModel _viewModel;
public WeatherForcastControl()
{
InitializeComponent();
_viewModel = new WeatherForcastViewModel();
this.DataContext = _viewModel;
}
}
这里是ModelView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;
}
问题是您将_forecastList设置为ObservableCollection的新实例。只需这样做:
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;
}
你改变了list属性引用的对象,而不是通过在该方法中将字段设置为新集合来告诉视图。
要么只在setter 或的通知中使用属性和注释,要么使其无法更改引用,这通常是最好的方法:
private readonly ObservableCollection<ForcastInfo> _forcastList = new ObservableCollection<ForcastInfo>();
public ObservableCollection<ForcastInfo> ForcastList
{
get { return _forcastList; }
}
现在你不能弄乱绑定,因为属性总是指向同一个对象。要用这个设置替换列表,只需调用Clear()
并添加新对象。