在我的UWP应用程序中，我有ListView增量加载。现在我还需要在ListViewItem中添加一个图像。我试着直接给它URI。
其中ThumbnailImage只是我视图模型中的一个字符串。这个问题是因为增量加载，当我在前一个图像仍在加载时向下滚动一点时，应用程序就会挂起。然而，如果我让所有图像出现然后向下滚动，它就可以正常工作。
我还尝试过该工具包中的ImageEx控件，它也有同样的问题。
我做了一些搜索，我在XAML中找到的唯一的东西是doing IsAsync = True。但似乎UWP中没有IsAsync。
我的ViewModel：
public class MyViewModel
{
...
public string ThumbnailImage { get; set; }
...
}
我的XAML ListView会逐渐填充
<ListView Grid.Row="0"
SelectionMode="Single"
IsItemClickEnabled="True"
ItemClick="SearchResultListView_ItemClick" >
<ListView.ItemContainerStyle>
<Style TargetType="ListViewItem">
<Setter Property="HorizontalContentAlignment" Value="Stretch"/>
<Setter Property="BorderBrush" Value="Gray"/>
<Setter Property="BorderThickness" Value="0, 0, 0, 1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ListViewItem">
<ListViewItemPresenter
ContentTransitions="{TemplateBinding ContentTransitions}"
SelectionCheckMarkVisualEnabled="True"
CheckBrush="{ThemeResource SystemControlForegroundBaseMediumHighBrush}"
CheckBoxBrush="{ThemeResource SystemControlForegroundBaseMediumHighBrush}"
DragBackground="{ThemeResource ListViewItemDragBackgroundThemeBrush}"
DragForeground="{ThemeResource ListViewItemDragForegroundThemeBrush}"
FocusBorderBrush="{ThemeResource SystemControlForegroundAltHighBrush}"
FocusSecondaryBorderBrush="{ThemeResource SystemControlForegroundBaseHighBrush}"
PlaceholderBackground="{ThemeResource ListViewItemPlaceholderBackgroundThemeBrush}"
PointerOverBackground="{ThemeResource SystemControlDisabledTransparentBrush}"
SelectedBackground="{ThemeResource SystemControlDisabledTransparentBrush}"
SelectedForeground="{ThemeResource SystemControlDisabledTransparentBrush}"
SelectedPointerOverBackground="{ThemeResource SystemControlDisabledTransparentBrush}"
PressedBackground="{ThemeResource SystemControlDisabledTransparentBrush}"
SelectedPressedBackground="{ThemeResource SystemControlDisabledTransparentBrush}"
DisabledOpacity="{ThemeResource ListViewItemDisabledThemeOpacity}"
DragOpacity="{ThemeResource ListViewItemDragThemeOpacity}"
ReorderHintOffset="{ThemeResource ListViewItemReorderHintThemeOffset}"
HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
ContentMargin="{TemplateBinding Padding}"
CheckMode="Inline"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ListView.ItemContainerStyle>
<ListView.ItemTemplate>
<DataTemplate x:DataType="viewModel:MyViewModel">
<UserControl >
<Grid Style="{StaticResource SomeStyle}">
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="VisualStateGroup">
<VisualState x:Name="VisualStatePhone">
<VisualState.StateTriggers>
<AdaptiveTrigger MinWindowWidth="0"/>
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="ThumbnailImage.Width" Value="50"/>
<Setter Target="ThumbnailImage.Height" Value="50"/>
</VisualState.Setters>
</VisualState>
<VisualState x:Name="VisualStateTablet">
<VisualState.StateTriggers>
<AdaptiveTrigger MinWindowWidth="600" />
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="ThumbnailImage.Width" Value="70"/>
<Setter Target="ThumbnailImage.Height" Value="70"/>
</VisualState.Setters>
</VisualState>
<VisualState x:Name="VisualStateDesktop">
<VisualState.StateTriggers>
<AdaptiveTrigger MinWindowWidth="1200" />
</VisualState.StateTriggers>
<VisualState.Setters>
<Setter Target="ThumbnailImage.Width" Value="90"/>
<Setter Target="ThumbnailImage.Height" Value="90"/>
</VisualState.Setters>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Grid.RowDefinitions>
<RowDefinition MaxHeight="30"></RowDefinition>
<RowDefinition MaxHeight="30"></RowDefinition>
<RowDefinition MaxHeight="30"></RowDefinition>
<RowDefinition MaxHeight="30"></RowDefinition>
<RowDefinition MaxHeight="30"></RowDefinition>
<RowDefinition MaxHeight="10"></RowDefinition>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Image Source="{x:Bind ThumbnailImage}"
Visibility="{x:Bind ThumbnailImage, Converter={StaticResource BoolToVisibilityImage}}"
Name="ThumbnailImage"/>
<TextBlock Text="{x:Bind Name}" .../>
<Grid Grid.Row="1"
Grid.Column="1"
Visibility="{x:Bind Source, Converter={StaticResource ConverterNameHere}}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{x:Bind lblSource, Mode=OneWay}" .../>
<TextBlock Text="{x:Bind Source}" .../>
</Grid>
<Grid Grid.Row="2"
Grid.Column="1"
Visibility="{x:Bind Author, Converter={StaticResource ConverterNameHere}}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{x:Bind lblAuthor, Mode=OneWay}" .../>
<TextBlock Text="{x:Bind Author}" .../>
</Grid>
<TextBlock Text="{x:Bind EducationalLevel}" .../>
<StackPanel Orientation="Horizontal"
Grid.Row="4"
Grid.Column="1">
<ItemsControl ItemsSource="{x:Bind AccessRights}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Image Source="{Binding}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<ItemsControl ItemsSource="{x:Bind Languages}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
<ItemsControl ItemsSource="{x:Bind TypeImages}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Image Source="{Binding}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>
</UserControl>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
这是我的增量加载类：
public class ItemsToShow : ObservableCollection<MyViewModel>, ISupportIncrementalLoading
{
private SearchResponse ResponseObject { get; set; } = new SearchResponse();
MyViewModel viewModel = null;
public bool HasMoreItems
{
get
{
if ((string.IsNullOrEmpty(SearchResultDataStore.NextPageToken) && !SearchResultDataStore.IsFirstRequest) || SearchResultDataStore.StopIncrementalLoading)
return false;
if(SearchResultDataStore.IsFirstRequest)
{
using (var db = new DbContext())
{
var json = db.UpdateResponse.First(r => r.LanguageId == DataStore.Language).JsonResponse;
Metadata = Newtonsoft.Json.JsonConvert.DeserializeObject<UpdateApiResponse>(json).response.metadata.reply;
}
var returnObject = SearchResultDataStore.SearchResponse;
ResponseObject = returnObject.response;
//This will show a grid with some message for 3 seconds on a xaml page named SearchResultPage.
Toast.ShowToast(ResponseObject.message, SearchResultPage.Current.ToastGrid);
}
else
{
SearchApiResponse returnObject = null;
try
{
returnObject = new SearchApiCall().CallSearchApiAsync(param1, param2, param3).Result;
}
catch
{
return false;
}
ResponseObject = returnObject.response;
}
try
{
return ResponseObject.documents.Count > 0;
}
catch { return false; }
}
}
public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
CoreDispatcher coreDispatcher = Window.Current.Dispatcher;
return Task.Run<LoadMoreItemsResult>(async () =>
{
await coreDispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
foreach (var item in ResponseObject.documents)
{
this.Add(PrepareViewModel(item));
}
});
await Task.Delay(350);
return new LoadMoreItemsResult() { Count = count };
}).AsAsyncOperation<LoadMoreItemsResult>();
}
public MyViewModel PrepareViewModel(Document document)
{
viewModel = new MyViewModel();
viewModel.property1 = document.value1;
viewModel.property2 = document.value2;
...
...
if(SearchResultDataStore.ShowImage)
{
//thumbnailUrl is a string.
viewModel.ThumbnailImage = document.thumbnailUrl;
}
else
{
viewModel.ThumbnailImage = "somegarbage.png";
}
...
...
return viewModel;
}
}
答案 0 :(得分：0)
默认情况下，当您使用x:Bind作为来源时，绑定不会自动更新。
要验证问题的根本原因，您可以在值转换器中设置断点，并查看调用的时间。
我建议使用x:Bind ThumbnailImage, Mode=OneWay
您可能必须在后面的代码中实现INotifyPropertyChanged。
答案 1 :(得分：0)
采取几个步骤：
将x:Phase属性添加到Image控件。设置比其他值最大（例如，所有是＆＃34; 0＆＃34;，设置＆＃34; 1＆＃34;等等）
将Mode=OneWay添加到Image，因为您应该知道何时更改属性。
使用依赖项属性Image向ImagePath控件添加控件扩展。什么时候改变财产 - ＆gt;开始异步加载来自网络的图像（例如HttpClient）。请求完成后 - ＆gt;获取内容并将其放入BitmapSource并将其放入Source的{{1}}属性。
确保原始图片的大小不超过Image控件的大小，因为如果它是真的 - ＆gt;用户界面将会挂起。