Xamarin - ListView中的某些图像在刷新时不呈现

Question

我有一个ListView，其中包含一个包含图像和文本的模板。 当我刷新列表时，有时会显示一些图像（随机）

如果我向下滚动列表并向上滚动以再次查看该项目，图像将会神奇地显示，因此图像已正确设置为该项目。

我尝试了ListViewCachingStrategy.RecycleElement和ListViewCachingStrategy.RetainElement，没有区别。

<ListView ItemsSource="{Binding Path=Results}"
          HasUnevenRows="True"
          IsPullToRefreshEnabled="True"
          RefreshCommand="{Binding RefreshCommand}"
          IsRefreshing="{Binding IsBusy, Mode=OneWay}">
     <ListView.ItemTemplate>
          <DataTemplate>
            <ViewCell>
              <Grid>
                <Grid.ColumnDefinitions>
                  <ColumnDefinition Width="1*"/> <!-- Image -->
                  <ColumnDefinition Width="3*"/> <!-- Message -->
                  <ColumnDefinition Width="1*"/> <!-- Date -->
                </Grid.ColumnDefinitions>

                <Grid.RowDefinitions>
                  <RowDefinition Height="Auto"/>
                  <RowDefinition Height="Auto"/>
                  <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>

                <!-- Image -->
                <Grid Grid.Column="0" Grid.Row="0" Grid.RowSpan="3"
                HorizontalOptions="FillAndExpand"
                BackgroundColor="#40000000">
                  <Image Source="{Binding Thumbnail}" 
                   VerticalOptions="Center"
                   Aspect="AspectFill"/>
                </Grid>


private async Task RefreshAsync()
    {
        try
        {
            IsBusy = true;
            _results.Clear();
            _results.AsyncQueryStarted();

            var result = await _client.QueryAsync<ReportResult>(_report);
            if (result != null)
            {
                try
                {
                    var items = new List<ResultItem>(result.Events.Count);
                    foreach (var res in result.Events)
                    {
                        result.EntityLookup.TryGetValue(res.Guid, out var name);
                        var item = new ResultItem(res.Guid, name, res.EventTime, res.Notes);
                        items.Add(item);
                    }

                    int itemWidth = (int)(PageWidth / ItemsPerRow);
                    // Sort them by timestamp (latest first)
                    foreach (var item in items.OrderByDescending(x => x.Timestamp))
                    {
                        item.ItemWidth = itemWidth;
                        _results.Add(item);
                    }
                }
                catch { }

                _results.AsyncQueryFinished(_results.Count == 0);
                RefreshView();
            }
        }
        catch (Exception ex)
        {
            Application.Current.Trace("Error occured while refreshing", ex, this);
        }
        finally
        {
            _requiresRefresh = false;
            IsBusy = false;
        }
    }

private async void RefreshView()
    {
        int itemWidth = (int)(PageWidth / ItemsPerRow);

        var requests = new List<ThumbnailItem>();
        var results = new List<ResultItem>(_results);
        foreach (var item in results)
        {
            item.ItemWidth = itemWidth;

            // Try to retrieve it from cache
            item.Thumbnail = await _thumbnailService.RetrieveAsync(item.Id, null, item.Timestamp);
        }            
    }