ObservableCollection 上的 OnPropertyChanged 不会刷新 CollectionView 内容

Question

问题

我的 ViewModel 中有一个 ItemsChangedObservableRangeCollection （它基本上是来自 MVVMHelpers 包的 ObservableRangeCollection，有一些额外的方法可以在集合中的项目更改时添加事件），并且在我的 Xaml 页面中有一个绑定到此集合的 CollectionView 。为了显示我的数据，我使用了一些转换器，当我第一次打开页面时，它们按预期工作。

当我稍后返回此页面并且我想刷新我的数据时，就会出现问题。尽管数据被清除和刷新，并且尽管在集合本身或包含的项目上调用了 OnPropertyChanged 事件（我什至尝试从添加用于调试的临时按钮手动调用它），但 CollectionView 并未更新，并且甚至没有调用转换器。

只是为了一点额外的上下文，我的 ObservableRangeCollection 中的数据实际上并没有改变：集合包含用户数据，转换器的作用是使用用户 ID 并获取一些可能会发生变化的分数；这就是为什么我尝试手动调用 OnPropertyChanged 来强制转换器刷新。

我的代码：

ContentPage 的摘录，其中包含 CollectionView 以及正在使用的不同转换器：

<ContentPage.Behaviors>
    <toolkit:EventToCommandBehavior Command="{Binding RefreshVMCommand}" EventName="Appearing"/>
</ContentPage.Behaviors>

<!-- [...] -->

<CollectionView x:Name="participantsListView" 
ItemsSource="{Binding CompetitorsBySelectedGroup }" 
SelectionMode="None" >
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <Grid x:DataType="model:Competitor" HeightRequest="76" >
                
                <!--Grid Row and Column Definitions-->

                <Label Grid.Column="0" Text="{Binding Number }"/>
                <Label Grid.Column="1" Text="{Binding FullName }"/>

                <Image Grid.Column="2" Source="task_list_check.svg" IsVisible="{Binding ., Converter={StaticResource IsResultScoreNotNullConverter}}"/>

                <Border Grid.Column="3" IsVisible="{Binding ., Converter={StaticResource IsResultScoreNotNullConverter}}">
                    <Label Text="{Binding ., Converter={StaticResource GetResultScore}}"/>
                </Border>
            </Grid>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

用于刷新数据的代码，从页面 OnAppearing 上的 ViewModel 调用：

[RelayCommand]
public void RefreshVM()
{
    CompetitorsBySelectedGroup?.Clear();
    var competitorList = DataManager.Instance.AppData.GetCompetitorsByCurrentGroup();
    CompetitorsBySelectedGroup.AddRange(competitorList ?? []);

    // Tentative to notify collection changed
    OnPropertyChanged(nameof(CompetitorsBySelectedGroup));

    // Tentative to notify directly items changed
    foreach (INotifyPropertyChanged item in CompetitorsBySelectedGroup)
    {
        OnPropertyChanged(nameof(item));
    }
}

我注意到一些有趣的事情，当我没有清除我的 ObservableCollection (
CompetitorsBySelectedGroup?.Clear()
)，而是重新定义它 (
CompetitorsBySelectedGroup = []
) 时，CollectionView 实际上会刷新，但出于某些寻址原因，我宁愿避免这样做。

我的 ItemsChangedObservableRangeCollection 的代码：

namespace MauiUtils
{
    /// <summary>
    ///     This class adds the ability to refresh the list when any property of
    ///     the objects changes in the list which implements the INotifyPropertyChanged. 
    /// </summary>
    /// <typeparam name="T"/>
    public class ItemsChangedObservableRangeCollection<T> : ObservableRangeCollection<T> where T : INotifyPropertyChanged
    {
        public delegate void ItemChangedEventHandler(object source, EventArgs args);

        /// <summary>
        /// Event fired when an item of the collection is updated
        /// </summary>
        public event ItemChangedEventHandler ItemChanged;

        protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
        {
            if (e.Action == NotifyCollectionChangedAction.Add)
            {
                RegisterPropertyChanged(e.NewItems);
            }
            else if (e.Action == NotifyCollectionChangedAction.Remove)
            {
                UnRegisterPropertyChanged(e.OldItems);
            }
            else if (e.Action == NotifyCollectionChangedAction.Replace)
            {
                UnRegisterPropertyChanged(e.OldItems);
                RegisterPropertyChanged(e.NewItems);
            }
            base.OnCollectionChanged(e);
        }

        protected override void ClearItems()
        {
            UnRegisterPropertyChanged(this);
            base.ClearItems();
        }

        private void RegisterPropertyChanged(IList items)
        {
            foreach (INotifyPropertyChanged item in items)
            {
                if (item != null)
                {
                    item.PropertyChanged += new PropertyChangedEventHandler(item_PropertyChanged);
                }
            }
        }

        private void UnRegisterPropertyChanged(IList items)
        {
            foreach (INotifyPropertyChanged item in items)
            {
                if (item != null)
                {
                    item.PropertyChanged -= new PropertyChangedEventHandler(item_PropertyChanged);
                }
            }
        }

        private void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            OnItemChange();
        }

        protected virtual void OnItemChange()
        {
            ItemChanged?.Invoke(this, EventArgs.Empty);
        }
    }
}

Answer 1

仔细阅读您的帖子，似乎您可能会竭尽全力刷新“应该”自动刷新的属性。问题是， ObservableRangeCollection<Competitor> 仅在添加或删除项目时触发

CollectionChanged

事件。但是您的

DataTemplate

（其中

FullName

和

Number

是绑定属性）需要响应

items

中的属性更改，而不是列表中的更改。

<DataTemplate>
    <Grid x:DataType="model:Competitor" HeightRequest="76" >  
        <Label Grid.Column="0" Text="{Binding Number }"/>
        <Label Grid.Column="1" Text="{Binding FullName }"/>
        <Image Grid.Column="2" Source="task_list_check.svg" IsVisible="{Binding ., Converter={StaticResource IsResultScoreNotNullConverter}}"/>
        <Border Grid.Column="3" IsVisible="{Binding ., Converter={StaticResource IsResultScoreNotNullConverter}}">
            <Label Text="{Binding ., Converter={StaticResource GetResultScore}}"/>
        </Border>
    </Grid>
</DataTemplate>

如果这些属性更改时刷新失败，那么怀疑就落在

Competitor

类本身上，它必须实现

INotifyPropertyChanged

（通常通过继承社区工具包中的

ObservableObject

）。

public class Competitor : INotifyPropertyChanged // Or inherit ObservableObject
{
    public string FullName
    {
        get => _fullName;
        set
        {
            if (!Equals(_fullName, value))
            {
                _fullName = value;
                OnPropertyChanged();
            }
        }
    }
    string _fullName = string.Empty;

    /// <summary>
    /// A string, to allow something like "RP-002916"
    /// </summary>
    public string Number
    {
        get => _number;
        set
        {
            if (!Equals(_number, value))
            {
                _number = value;
                OnPropertyChanged();
            }
        }
    }
    string _number = string.Empty;

    /// <summary>
    /// A string, for expediency for testing, allow direct formatted entry
    /// </summary>
    public string? Score
    {
        get => _score;
        set
        {
            if (!Equals(_score, value))
            {
                _score = value;
                OnPropertyChanged();
                OnPropertyChanged(nameof(IsScoreVisible));
            }
        }
    }
    string? _score = string.Empty;

    public bool IsScoreVisible => !string.IsNullOrEmpty(_score);

    protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null) =>
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    public event PropertyChangedEventHandler? PropertyChanged;
}

最小示例

这里有一个最小的 Android 示例来解释“自动刷新自身”的含义。首先，创建一个包含五个

Competitor

对象的集合视图，其中两个没有分数。然后在 [Casey Taylor] 卡上向左滑动以调用

MainPage.xaml

中定义的乐谱编辑器覆盖层。

乐谱编辑器绑定到传递到

Competitor

命令的

EditScores

的属性，但乐谱本身除外，在这种情况下，会创建一个副本以便能够恢复。如果单击

Apply

按钮，我们会将预览值复制到实际的

Competitor.Score

中。

关于你的问题

ObservableCollection不会刷新CollectionView内容

，我的观点是，当我们返回到CollectionView时，不需要刷新任何东西。由于

INotifyPropertyChanged

对

Competitor

类的操作，这应该已经得到解决。如果它不令人耳目一新，这就是您想要查看的地方。

测试代码

注意：我不明白哪里需要

IValueConverter 转换器来有条件地显示分数，因此这个基本示例不包含任何转换器。

查看

`public partial class MainPage : ContentPage { public MainPage() => InitializeComponent(); protected override void OnAppearing() { base.OnAppearing(); } new MainPageBindingContext BindingContext => (MainPageBindingContext)base.BindingContext; protected override bool OnBackButtonPressed() { if(BindingContext.IsEditingScore) { BindingContext.IsEditingScore = false; return true; } return base.OnBackButtonPressed(); } }`

型号

class MainPageBindingContext : INotifyPropertyChanged { public MainPageBindingContext() { EditScoreCommand = new Command<Competitor>(OnEditScore); ApplyCommand = new Command(OnApply); CancelCommand = new Command(OnCancel); } /// <summary> /// ObservableRangeCollection is used in OPs question, but for this /// sample there's no reason you couldn't simply use ObservableCollection /// </summary> public ObservableRangeCollection<Competitor> CompetitorsBySelectedGroup { get; } = new ObservableRangeCollection<Competitor>() { new Competitor{ FullName = "Alex Johnson", Number = "AJ-001234", Score = "85" }, new Competitor{ FullName = "Jamie Lee", Number = "JL-001235", Score = "90" }, new Competitor{ FullName = "Morgan Smith", Number = "MS-001236" }, new Competitor{ FullName = "Casey Taylor", Number = "CT-001237" }, new Competitor{ FullName = "Jordan Brown", Number = "JB-001238", Score = "80" } }; public ICommand EditScoreCommand { get; } private void OnEditScore(Competitor competitor) { IsEditingScore = true; // Work with a copy so that Cancel can leave original unchanged. ScorePreview = competitor.Score; EditTarget = competitor; } public ICommand ApplyCommand { get; private set; } private void OnApply(object o) { EditTarget.Score = ScorePreview; IsEditingScore = false; } public ICommand CancelCommand { get; private set; } private void OnCancel(object o) => IsEditingScore = false; public Competitor EditTarget { get => _editTarget; set { if (!Equals(_editTarget, value)) { _editTarget = value; OnPropertyChanged(); } } } Competitor _editTarget = default; public bool IsEditingScore { get => _isEditingScore; set { if (!Equals(_isEditingScore, value)) { _isEditingScore = value; OnPropertyChanged(); OnPropertyChanged(nameof(IsNotEditingScore)); } } } bool _isEditingScore = default; /// <summary> /// Editing value for score that can be reverted on cancel. /// </summary> public string? ScorePreview { get => _scorePreview; set { if (!Equals(_scorePreview, value)) { _scorePreview = value; OnPropertyChanged(); } } } string? _scorePreview = string.Empty; public bool IsNotEditingScore => !IsEditingScore; protected virtual void OnPropertyChanged([CallerMemberName] string? propertyName = null) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)); public event PropertyChangedEventHandler? PropertyChanged; }

XAML

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:local="clr-namespace:RefreshCompetitors" x:Class="RefreshCompetitors.MainPage" Shell.NavBarIsVisible="{Binding IsNotEditingScore}"> <ContentPage.BindingContext> <local:MainPageBindingContext x:Name="Page"/> </ContentPage.BindingContext> <Grid> <VerticalStackLayout Padding="5,0" Spacing="25"> <Image Source="dotnet_bot.png" HeightRequest="185" Aspect="AspectFit" /> <CollectionView ItemsSource="{Binding CompetitorsBySelectedGroup }" SelectionMode="None" BackgroundColor="Azure"> <CollectionView.ItemTemplate> <DataTemplate> <SwipeView Threshold="50">  <SwipeView.RightItems> <SwipeItems Mode="Execute"> <SwipeItemView Command="{Binding EditScoreCommand, Source={x:Reference Page}}" CommandParameter="{Binding .}"> <Grid WidthRequest="50" BackgroundColor="Aqua" RowDefinitions=","> <Label Text="✎" FontSize="18" TextColor="Black" VerticalTextAlignment="Center" HorizontalTextAlignment="Center"/> <Label Grid.Row="1" TextColor="Black" Text="Score" FontSize="10" VerticalTextAlignment="Center" HorizontalTextAlignment="Center" VerticalOptions="Center"/> </Grid> </SwipeItemView> </SwipeItems> </SwipeView.RightItems> <Grid Margin="10,5" BackgroundColor="White" ColumnDefinitions="Auto,Auto," RowDefinitions="Auto, Auto" MinimumHeightRequest="40" RowSpacing="4"> <Label MinimumWidthRequest="100" Padding="20,0,0,0" Grid.Column="0" VerticalOptions="Center" HorizontalTextAlignment="Start" Text="{Binding Number }"/> <Label MinimumWidthRequest="150" Padding="20,0,0,0" Grid.Column="1" VerticalOptions="Center" HorizontalTextAlignment="Start" Text="{Binding FullName }"/> <CheckBox IsVisible="{Binding IsScoreVisible}" Grid.Row="1" Grid.Column="0" IsChecked="True" HorizontalOptions="Start"/> <Border IsVisible="{Binding IsScoreVisible}" Grid.Row="1" MinimumWidthRequest="100" Grid.Column="1" StrokeThickness="4"> <Label Padding="20,0,0,0" VerticalOptions="Center" HorizontalTextAlignment="Start" Text="{Binding Score}"/> </Border> </Grid> </SwipeView> </DataTemplate> </CollectionView.ItemTemplate> </CollectionView> </VerticalStackLayout>  <Grid IsVisible="{Binding IsEditingScore}" BackgroundColor="Black" RowDefinitions="60,50,,Auto,Auto, 100"> <Label HorizontalTextAlignment="Start" Text="{Binding EditTarget.FullName}" TextColor="White" FontSize="Title" Padding="20,20,0,0"/> <Label HorizontalTextAlignment="Start" Text="{Binding EditTarget.Number}" TextColor="White" FontSize="Subtitle" Padding="20,20,0,0" Grid.Row="1"/> <Entry VerticalOptions="Center" Placeholder="Score or Other" WidthRequest="250" FontSize="Subtitle" BackgroundColor="White" TextColor="Black" Grid.Row="2" Text="{Binding ScorePreview}"/> <Button Text="Apply" WidthRequest="100" HeightRequest="40" CornerRadius="20" Grid.Row="3" Margin="0,10" Command="{Binding ApplyCommand}"/> <Button Text="Cancel" WidthRequest="100" HeightRequest="40" CornerRadius="20" Grid.Row="4" Margin="0,10" Command="{Binding CancelCommand}"/> </Grid> </Grid> </ContentPage>

ObservableCollection 上的 OnPropertyChanged 不会刷新 CollectionView 内容

问题描述投票：0回答：1

问题

我的代码：

1个回答

这里有一个最小的 Android 示例来解释“自动刷新自身”的含义。首先，创建一个包含五个

最新问题

ObservableCollection 上的 OnPropertyChanged 不会刷新 CollectionView 内容

问题描述 投票：0回答：1

问题

我的代码：

1个回答

这里有一个最小的 Android 示例来解释“自动刷新自身”的含义。首先，创建一个包含五个

最新问题

问题描述投票：0回答：1