【发布时间】：2016-04-12 15:24:44
【问题描述】：
我觉得我遇到的问题很奇怪。
我有一个使用 MVVM 模式的 WPF 应用程序。
我使用 Linq-to-SQL 从我的数据库中检索数据，并使用绑定在 ListBox 中显示描述字段数据。
它有效，但不完全。由于某种原因，最后一条记录不显示。我已经验证它是从数据库中获取的。无法选择；它根本不存在。
让记录出现的唯一方法是将焦点设置到 ListBox 并滚动鼠标滚轮或使用键盘实际向下移动以越过最后一条记录（应该是倒数第二条记录）。一旦你这样做了，记录就会出现。
另一种显示记录的方法是更新列表框中的任何记录。我有一个 TextBox 以双向模式绑定到 ListBox 的 SelectedItem，所以当我选择一个项目时，更改 TextBox 中的文本并单击更新按钮，它会调用命令来进行数据库更新，效果很好，但是最后一条记录的缺失记录也会出现。
ListBox 和 ListView 是否存在渲染问题，因为我都试过了？为什么 ListBox 似乎需要在最后一个项目出现之前“重绘”？
CategoryModel.cs
public class CategoryModel
{
public int CategoryID { get; set; }
public string Description { get; set; }
public List<CategoryModel> categories = new List<CategoryModel>();
readonly SalesLinkerDataContext _dbContext = new SalesLinkerDataContext();
public void GetCategories()
{
categories.Clear();
var result = _dbContext.tblSalesCategories.ToList();
foreach (var item in result)
{
categories.Add(new CategoryModel
{
CategoryID = item.CategoryID,
Description = item.Description.Trim()
});
}
}
internal void Update(CategoryModel cm)
{
try
{
var category = (from a in _dbContext.tblSalesCategories
where a.CategoryID == cm.CategoryID
select a).FirstOrDefault();
if (category != null)
{
category.Description = cm.Description;
_dbContext.SubmitChanges();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
}
CategoriesViewModel.cs
public class CategoriesViewModel : ViewModelBase, IPageViewModel
{
public CategoryModel Categories = new CategoryModel();
private DelegateCommand _getCategoriesCommand;
private DelegateCommand _updateCategoryCommand;
/// <summary>
/// Describes the name that will be used for the menu option
/// </summary>
public string Name
{
get { return "Manage Categories"; }
}
public string Description
{
get { return Categories.Description; }
set
{
Categories.Description = value;
OnPropertyChanged("Description");
}
}
public List<CategoryModel> ReceivedCategories
{
get { return Categories.categories; }
set
{
Categories.categories = value;
OnPropertyChanged("ReceivedCategories");
}
}
public ICommand GetCategoriesCommand
{
get
{
if (_getCategoriesCommand == null)
{
_getCategoriesCommand = new DelegateCommand(GetCategories, CanGetCategories);
}
return _getCategoriesCommand;
}
}
private bool CanGetCategories()
{
return true;
}
private void GetCategories()
{
Categories.GetCategories();
ReceivedCategories = Categories.categories;
}
public ICommand UpdateCategoryCommand
{
get
{
if (_updateCategoryCommand == null)
{
_updateCategoryCommand = new DelegateCommand(UpdateCategory, CanUpdateCategory);
}
return _updateCategoryCommand;
}
}
private bool CanUpdateCategory()
{
return true;
}
private void UpdateCategory()
{
Categories.Update(Categories);
}
}
CategoriesView.xaml
<UserControl x:Class="SalesLinker.CategoriesView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="600" Background="White" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="Loaded">
<i:InvokeCommandAction Command="{Binding GetCategoriesCommand}" />
</i:EventTrigger>
</i:Interaction.Triggers>
<Grid >
<Grid.RowDefinitions>
<RowDefinition Height="45"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="250"/>
<ColumnDefinition Width="100"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label Grid.Row="0" Grid.Column="0" Margin="20,0,0,0" FontSize="20" HorizontalAlignment="Center" Content="Categories"/>
<ListView x:Name="LstCategories" ItemsSource="{Binding ReceivedCategories, Mode=TwoWay}" Grid.Column="0" Grid.Row="1"
VerticalAlignment="Stretch"
Background="LightGray"
ScrollViewer.HorizontalScrollBarVisibility="Disabled"
SelectionChanged="LstCategories_OnSelectionChanged">
<ListView.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" VerticalAlignment="Stretch" >
<TextBlock Text="{Binding Description }"/>
</StackPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<Button Command="{Binding AddCategoryCommand}" Grid.Column="1" Grid.Row="1" VerticalAlignment="Top" Height="50" Width="50" Margin="0,20,0,0" Background="Transparent" BorderThickness="0" BorderBrush="Transparent" >
<Image Source="/Images/Plus.png"/>
</Button>
<Button Command="{Binding RemoveCategoryCommand}" Grid.Column="1" Grid.Row="1" VerticalAlignment="Top" Height="50" Width="50" Margin="0,75,0,0" Background="Transparent" BorderThickness="0">
<Image Source="/Images/Minus.png"/>
</Button>
<Grid Grid.Row="1" Grid.Column="2">
<Grid.RowDefinitions>
<RowDefinition Height="30"/>
<RowDefinition Height="50"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="75"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Label VerticalAlignment="Center" HorizontalAlignment="Center" Grid.Row="0" Grid.Column="0" Content="Description:"/>
<TextBox DataContext="CategoryModel" Grid.Row="0" Grid.Column="1" Width="250" Height="Auto" VerticalAlignment="Center" HorizontalAlignment="Left" Margin="10,0,0,0"
Text="{Binding SelectedItem.Description, ElementName=LstCategories}"/>
<Button Command="{Binding UpdateCategoryCommand}"
Grid.Row="1" Grid.Column="1" HorizontalAlignment="Left" Margin="10,0,0,0" Height="20" Width="120" Content="Update Description"/>
</Grid>
</Grid>
我对 MVVM 很陌生，所以希望我只是没有看到简单的东西。
【问题讨论】：
-
代码看起来不错。尝试临时排除使用 _dbContext：生成具有已知元素计数的假列表并查看结果。
-
结果相同，最后一项不显示。