我在 WPF 用戶控制元件中有 ItemsControl 和 DataGrid。這就是它的樣子
當按下“添加到卡片”按鈕時，一個 ViewModel 實體被添加到系結到 DataGrid 的 ObservableCollection 中。
<ItemsControl
ItemsSource="{Binding Meals}"
x:Name="MealList"
Margin="5">
<ItemsControl.ItemTemplate>
<DataTemplate>
<components:MealCardCustomer
BorderBrush="OrangeRed"
BorderThickness="5px"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
<ScrollViewer
HorizontalScrollBarVisibility="Auto"
VerticalScrollBarVisibility="Disabled">
<DataGrid
HorizontalAlignment="Stretch"
IsReadOnly="True"
Background="Orange"
x:Name="OrderedMeals"
SelectionMode="Single"
ItemsSource="{Binding OrderedMeals, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}"
SelectedIndex="{Binding SelectedOrderedMeal, UpdateSourceTrigger=PropertyChanged, Mode=OneWayToSource}"
FontSize="26"
Grid.Column="0"
Grid.Row="0"
Margin="5"
AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridTextColumn Binding="{Binding Name, Mode=OneWay}" Header="Name" />
<DataGridTextColumn Binding= "{Binding Price, Mode=OneWay}" Header="Price" />
<DataGridTextColumn Binding="{Binding Ingredients, Mode=OneWay}" Header="Ingredients" />
</DataGrid.Columns>
</DataGrid>
</ScrollViewer>
問題是，有時當我添加新專案時，它看起來像一個空列。
我試圖添加一個重繪 資料網格的按鈕，但是當按下它時，它會使所有專案變為空白。
此外，我將 DataGrid 包裝在帶有水平滾動的 ScrollViewer 中，由于某種原因它不起作用。
那就是View的ViewModel
private string? address;
public string? Address
{
get { return address; }
set { address = value; OnPropertyChaneg(nameof(Address)); }
}
private int selectedOrderedMeal = -1;
public int SelectedOrderedMeal
{
get { return selectedOrderedMeal; }
set { selectedOrderedMeal = value; OnPropertyChaneg(nameof(SelectedOrderedMeal)); }
}
private ObservableCollection<MealCardCustomerViewModel> meals;
public ObservableCollection<MealCardCustomerViewModel> Meals
{
get { return meals; }
set { meals = value; }
}
private ObservableCollection<MealCardCustomerViewModel> orderedMeals;
public ObservableCollection<MealCardCustomerViewModel> OrderedMeals
{
get { return orderedMeals; }
set { orderedMeals = value; OnPropertyChaneg(nameof(OrderedMeals)); }
}
public BaseCommand RemoveCommand { get; }
public BaseCommand FinishOrderCommand { get; }
public NavigateCommand NavigateToCustomerListOfOtders { get; }
public BaseCommand LoadMealsCommand { get; }
public CustomerOrderingViewModel(NavigationService customerListOfOrdersNavigationService, NavigationService helpNavigationService, IMealService mealService)
: base(helpNavigationService, mealService)
{
Meals = new ObservableCollection<MealCardCustomerViewModel>();
OrderedMeals = new ObservableCollection<MealCardCustomerViewModel>();
RemoveCommand = new RemoveMeal(this);
FinishOrderCommand = new FinishOrder(this, customerListOfOrdersNavigationService);
NavigateToCustomerListOfOtders = new NavigateCommand(customerListOfOrdersNavigationService);
LoadMealsCommand = new LoadMeals<CustomerOrderingViewModel>(this);
}
public static CustomerOrderingViewModel LoadViewModel(NavigationService customerListOfOrders, NavigationService helpNavigationService, IMealService mealService)
{
CustomerOrderingViewModel viewModel = new CustomerOrderingViewModel(customerListOfOrders, helpNavigationService, mealService);
viewModel.LoadMealsCommand.Execute(null);
return viewModel;
}
public override void LoadMealsList(List<Meal> meals)
{
Meals.Clear();
foreach (var meal in meals)
{
Meals.Add(new MealCardCustomerViewModel(meal,this));
}
}
像 ItemsControl 的 ItemTemplates 的視圖
<Image
Source="{Binding MealImage, Converter ={StaticResource imageConverter}, Mode=TwoWay, TargetNullValue=DefaultImage}"
Stretch="Uniform"/>
<DockPanel
Grid.Row="1"
VerticalAlignment="Center"
Margin="5">
<TextBlock
FontSize="20"
Margin="5"
Text="Name :"/>
<TextBox
Text="{Binding Name,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
FontSize="20"
Margin="5"/>
</DockPanel>
<DockPanel
Grid.Row="2"
VerticalAlignment="Center"
Margin="5">
<TextBlock
FontSize="20"
Margin="5"
Text="Price :"/>
<TextBox
Text="{Binding Price, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, StringFormat={}{0:f2}}"
FontSize="20"
Margin="5"/>
</DockPanel>
<DockPanel
Grid.Row="3"
VerticalAlignment="Center"
Margin="5">
<TextBlock
FontSize="20"
Margin="5"
Text="Ingredients:"/>
<TextBox
Text="{Binding Ingredients, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
FontSize="20"
Margin="5"
TextWrapping="Wrap"
VerticalScrollBarVisibility="Visible"
HorizontalScrollBarVisibility="Visible"
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch"
/>
</DockPanel>
<Button
Command="{Binding AddToCardCommand}"
Background="OrangeRed"
Grid.Row="4"
Margin="10 5 10 5"
Content="Add to cart"
FontSize="20"/>
這就是將專案添加到 ObservableCollection 的命令
private CustomerOrderingViewModel customerOrderingViewModel;
private MealCardCustomerViewModel mealCardCustomerViewModel;
public AddToCard(CustomerOrderingViewModel customerOrderingViewModel, MealCardCustomerViewModel mealCardCustomerViewModel)
{
this.customerOrderingViewModel = customerOrderingViewModel;
this.mealCardCustomerViewModel = mealCardCustomerViewModel;
}
public override void Execute(object? parameter)
{
customerOrderingViewModel.OrderedMeals.Add(mealCardCustomerViewModel);
}
uj5u.com熱心網友回復：
問題在于物件中的影像現在不存在，因此它們為空。
由于某種原因，空值導致轉換器中的無限回圈，因此視圖模型無法加載物體的屬性，但集合可以讀取計數已更改，從而顯示空行。
uj5u.com熱心網友回復：
將商品添加到購物車的方式不是執行緒安全的。
想象一下AddToCart()被稱為 wich 的東西會更新你的customerOrderingViewModeland mealCardCustomerViewModel。然后想象一下，在Execute呼叫之前，其他一些執行緒發生了變化customerOrderingViewModel或mealCardCustomerViewModel. 這可能會導致在您的訂單中Execute()添加錯誤（或Null）餐點。如果這是您的錯誤的原因，下面的代碼應該解決它：
public AddToCard(CustomerOrderingViewModel customerOrderingViewModel, MealCardCustomerViewModel mealCardCustomerViewModel)
{
customerOrderingViewModel.OrderedMeals.Add(mealCardCustomerViewModel);
this.customerOrderingViewModel = customerOrderingViewModel;
this.mealCardCustomerViewModel = mealCardCustomerViewModel;
}
如果您不需要customerOrderingViewModel并且mealCardCustomerViewModel在擁有的類中AddToCart()，您甚至可以完全保留這些變數。
旁注：如果您不打算更改可觀察集合而只更改其內容，則可以簡單地將它們宣告為公共欄位而不是屬性。只有當整個 ObservableCollection 物件被更改時，屬性的設定器才會被訪問，但如果其內容被更改，則不會被訪問。ObservableCollection 內部更改的 PropertyChanged 通知由 ObservableCollection 實作處理。
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