Question

我已经成功地将一个项目添加到MVVM列表中，现在我的问题是维护视图模型中的列表。每次我导航到页面或返回页面并返回到列表视图时，列表都会重置。我将如何实现这一目标？我目前正在使用棱镜来构建MVVM。

ViewModel：

public ObservableCollection<CartData> _cartData;

public ObservableCollection<CartData> CartData
        {

         get {
             return _cartData;
             }
        set {

                SetProperty(ref _cartData, value);
           }
        }




        private DelegateCommand _addItemCommand;
        public ICommand AddItemCommand
        {
            get
            {
                if (_addItemCommand == null)
                {
                    _addItemCommand = new DelegateCommand(AddToCart);
                }
                return _addItemCommand;
            }
        }

        public void AddToCart() {

            CartData.Add(new CartData { Cakename = "Black Forest", Cakeprice = 104 });
                   }

查看：

 .....

 <Page.DataContext>
        <vm:CartingDataSource/>
    </Page.DataContext>
   ....
<ListView
            x:Name="itemListView"
            AutomationProperties.AutomationId="ItemsListView"
            AutomationProperties.Name="Items"
            TabIndex="1"
            Margin="-10,130,0,264"
            Padding="120,0,0,60"

            ItemsSource="{Binding cartData}"
            IsSwipeEnabled="False" Grid.RowSpan="2" ItemClick="itemListView_ItemClick" SelectionChanged="itemListView_SelectionChanged_1" IsItemClickEnabled="True">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid Margin="6">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto"/>
                            <ColumnDefinition Width="*"/>
                        </Grid.ColumnDefinitions>
                        <Border Background="{ThemeResource ListViewItemPlaceholderBackgroundThemeBrush}" Width="60" Height="60">
                            <Image Stretch="UniformToFill" AutomationProperties.Name="{Binding Title}" Source="Assets/wewewew.jpg"/>
                        </Border>
                        <StackPanel Grid.Column="1" Margin="10,0,0,0">
                            <TextBlock Text="{Binding Cakename}" Style="{StaticResource TitleTextBlockStyle}" TextWrapping="NoWrap" MaxHeight="40"/>
                            <TextBlock Text="{Binding Cakeprice}" Style="{StaticResource CaptionTextBlockStyle}" TextWrapping="NoWrap"/>
                        </StackPanel>
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>
            <ListView.ItemContainerStyle>
                <Style TargetType="FrameworkElement">
                    <Setter Property="Margin" Value="0,0,0,10"/>
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>

Answer 1

此处如果您的ViewModel为CartingDataSource，则在每次页面加载时都会对其进行实例化。现在，如果是这种情况，那么您将在构造函数中创建集合的新实例，如下所示：

public CartingDataSource() {


        CartData = new ObservableCollection<CartData>();

      }

因此，它会重新初始化您的收藏。

您需要从构造函数中删除初始化并执行以下操作：

public ObservableCollection<CartData> _cartData;

public ObservableCollection<CartData> cartData
    {

     get {
            if(_cartData == null)
            {
                 _cartData = new ObservableCollection<CartData>();
            } 
         return _cartData;
         }
    set {

            _cartData = value;
       }
    }

在List / ObservableCollection中维护集合

1 个答案: