mvvm - CollectionView RemainingItemsThreshholdReached 命令出错

问题描述

我在我的应用程序中使用 Prism MVVM。所以这是我的 XAML 代码

 IsRefreshing="{Binding IsRefreshing}"
                 Command="{Binding RefreshCommand}">

        <CollectionView ItemsSource="{Binding Images}"
                        RemainingItemsThreshold="1"
                        RemainingItemsThresholdReachedCommand="{Binding UpdateImagesCommand}">
        <CollectionView.ItemsLayout>
            <GridItemsLayout Orientation="Vertical"
                             Span="3"/>
        </CollectionView.ItemsLayout>
        <CollectionView.ItemTemplate>
            <DataTemplate>
                <Grid Padding="2">
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>
                <ff:CachedImage 
                    Grid.Row="0"
                    Grid.Column="0"
                    HorizontalOptions="Center"
                    VerticalOptions="Center"
                    Aspect="AspectFill"
                    Source="{Binding Source, Mode=OneWay}">
                    <ff:CachedImage.Transformations>
                            <ffTransformations:CropTransformation />
                        </ff:CachedImage.Transformations>
                </ff:CachedImage>
                </Grid>
            </DataTemplate>
        </CollectionView.ItemTemplate>
    </CollectionView>
    </RefreshView>

正如您在此处看到的，我的参数 RemainingItemsThreshold 的值为“1”，并将 anUpdateImagesCommand 绑定到 RemainingItemsThresholdReachedCommand

这是此 xaml 页面的视图模型中的代码的一部分

private ObservableCollection _images;
public ObservableCollection Images
{
get { return _images; }
set { SetProperty(ref _images, value); }
}
private DelegateCommand _refreshCommand;
public DelegateCommand RefreshCommand =>
_refreshCommand ?? (_refreshCommand = new DelegateCommand(ExecuteRefreshCommand));
 private DelegateCommand _updateImagesCommand;
    public DelegateCommand UpdateImagesCommand =>
        _updateImagesCommand ?? (_updateImagesCommand = new DelegateCommand(ExecuteUpdateImagesCommand));
void ExecuteUpdateImagesCommand()
{
//Image im = new Image();
//im.Source = "Huayra3.jpg";
//Image im7 = new Image();
//im7.Source = "Huayra1.jpg";
 //Images.Add(im7);
        //Images.Add(im7);
        //Images.Add(im);
        //Images.Add(im);
        //Images.Add(im);
        //Images.Add(im);
    }
void ExecuteRefreshCommand()
{
// refresh posts feed command
IsRefreshing = false;
}

public AccountPageViewModel(INavigationService navigationService, IUserDataService userDataService) :
base(navigationService)
{
_userDataService = userDataService;
CurrentUser = userDataService.CurrentUser;
if (String.IsNullOrEmpty(this.CurrentUser.ImagePath))
        {
            this.CurrentUser.ImagePath = "user_avatar.jpg";     
        }

        Images = new ObservableCollection<Image>();

        Image im = new Image();
        im.Source = "Huayra3.jpg";
        Images.Add(im);
        Image im1 = new Image();
        im1.Source = "Huayra1.jpg";
        Images.Add(im1);
        Image im2 = new Image();
        im2.Source = "Huayra4.jpg";
        Images.Add(im2);
        Image im3 = new Image();
        im3.Source = "Huayra3.jpg";
        Images.Add(im3);
        Image im4 = new Image();
        im4.Source = "Huayra1.jpg";
        Images.Add(im4);
        Image im5 = new Image();
        im5.Source = "Huayra4.jpg";
        Images.Add(im5);
        Image im6 = new Image();
        im6.Source = "Huayra3.jpg";
        Images.Add(im6);
        Image im7 = new Image();
        im7.Source = "Huayra1.jpg";
        Images.Add(im7);
        Images.Add(im7);

        Images.Add(im7);
        Images.Add(im7);
        Images.Add(im7);
        Images.Add(im7);
        Images.Add(im7);
        Images.Add(im);


        //Images.Add(im);
        //Images.Add(im);

    }

如您所见，我在 VIewModel 构造函数中编写了一些值并将其添加到列表中。我阅读了有关 CollectionView 的 Microsoft 文档，并且我知道 UpdateImagesCommand 仅在达到 RemainingItemsThreshold 时才会执行。但是当我导航到此页面时，当我在标签页中的页面之间随机导航时，ExecuteUpdateImagesCommand() 会调用。这不应该，但我不知道发生这种情况的原因。smbd可以帮我吗？

标签： mvvmxamarin.formsxamarin.androidprismcollectionview

mvvm - CollectionView RemainingItemsThreshholdReached 命令出错

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