Question

我怀疑错误“无法创建MainViewModel的实例”是罪魁祸首，但说实话，我不确定。这是Visual Studio给我的唯一错误，代码编译并运行尽管它;我遇到的问题是我的列表框没有显示我的表中的数据。

MainPage.xaml的相关示例：

<phone:PhoneApplicationPage 
    x:Class="CarpetQuote.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
    d:DataContext="{d:DesignData SampleData/MainViewModelSampleData.xaml}" />

    <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
        <ListBox x:Name="MainListBox" Margin="0,0,-12,0" ItemsSource="{Binding Carpets}" SelectionChanged="MainListBox_SelectionChanged" >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding carpetName}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</phone:PhoneApplicationPage>

下面的MainViewModelSampleData.xaml;这是负责“无法创建MainViewModel实例”的页面。

<local:MainViewModel 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:CarpetQuote"
    SampleProperty="Sample Value">

    <local:MainViewModel.Items>
        <local:ItemViewModel LineOne="design one" LineTwo="Maecenas praesent accumsan bibendum" LineThree="Maecenas praesent accumsan bibendum dictumst eleifend facilisi faucibus habitant inceptos interdum lobortis nascetur"/>
        <local:ItemViewModel LineOne="design two" LineTwo="Dictumst eleifend facilisi faucibus" LineThree="Pharetra placerat pulvinar sagittis senectus sociosqu suscipit torquent ultrices vehicula volutpat maecenas praesent"/>
        <local:ItemViewModel LineOne="design three" LineTwo="Habitant inceptos interdum lobortis" LineThree="Accumsan bibendum dictumst eleifend facilisi faucibus habitant inceptos interdum lobortis nascetur pharetra placerat"/>
        <local:ItemViewModel LineOne="design four" LineTwo="Nascetur pharetra placerat pulvinar" LineThree="Pulvinar sagittis senectus sociosqu suscipit torquent ultrices vehicula volutpat maecenas praesent accumsan bibendum"/>
        <local:ItemViewModel LineOne="design five" LineTwo="Sagittis senectus sociosqu suscipit" LineThree="Dictumst eleifend facilisi faucibus habitant inceptos interdum lobortis nascetur pharetra placerat pulvinar sagittis"/>
        <local:ItemViewModel LineOne="design six" LineTwo="Torquent ultrices vehicula volutpat" LineThree="Senectus sociosqu suscipit torquent ultrices vehicula volutpat maecenas praesent accumsan bibendum dictumst eleifend"/>
    </local:MainViewModel.Items>
</local:MainViewModel>

我在其他地方读过一些关于错误的内容，但似乎没有什么帮助。一般的共识似乎是编译器不喜欢我的MainViewModel构造函数中的东西，但是我唯一的那一行db = new CarpetContext(App.ConnString);是必需的，并且我在另一个项目中没有错误地运行功能相同的代码。

如果这个错误不应该归咎于失败的绑定，这里是App.xaml.cs的相关部分，其中创建了数据库。

public partial class App : Application
{
    private static MainViewModel viewModel = null;

    public static MainViewModel ViewModel
    {
        get
        {
            if (viewModel == null)
            {
                viewModel = new MainViewModel();
            }

            return viewModel;
        }
    }

    private static string connString = null;
    public static string ConnString { get { return connString; } }
    public App()
    {
        // Autogenerated code and comments snipped

        if (connString == null)
        {
            connString = Resources["IsoDBConn"] as string;
        }
        createDB();
    }

    private void createDB()
    {
        using (var db = new CarpetContext(ConnString))
        {
            if (!db.DatabaseExists())
            {
                db.CreateDatabase();
            }
        }
    }

    private void Application_Activated(object sender, ActivatedEventArgs e)
    {
        if (!App.ViewModel.isDataLoaded)
        {
            App.ViewModel.loadData();
        }
    }
}

最后（我觉得代码之墙真的很糟糕），来自MainViewModel的引用函数。

public bool IsDataLoaded
{
    get;
    private set;
}

public void loadData()
{
    db.Carpets.InsertOnSubmit(new Carpet("StainMaster", 10));
    db.Carpets.InsertOnSubmit(new Carpet("Windsor", 12));
    db.Carpets.InsertOnSubmit(new Carpet("Homfray", 11.5m));
    db.Carpets.InsertOnSubmit(new Carpet("Wall Street", 15));
    db.Carpets.InsertOnSubmit(new Carpet("Axminster", 16.5m));
    db.SubmitChanges();
    Carpets = new ObservableCollection<Carpet>(db.Carpets.ToList());
    this.isDataLoaded = true;
}

Answer 1

好的，这是一个奇怪的，但我在另一台计算机上正在研究它......它运作良好。

原来问题在于我的Windows Phone SDK安装。列表框确实填充，但文本不可见。

这可能太局部化而无用，建议关闭。

表 - 列表框数据绑定不会导致显示数据

1 个答案: