UserControl 不显示数据

Question

我看不到 uc，我可以看到它，但它很干净，它不是空的，因为它显示空的 uc 对象（数据库中正确的记录数）但它只发生在使用 uc 的情况下，如果我使用没有 uc 的简单数据绑定，我可以看到每条记录。我已经做了一个断点来查看是否由于某种原因与依赖项属性一起传递的数据为空，但是对象中有所有信息，只是它无法将数据传递给 uc xaml.

已经在没有 uc 的情况下尝试过并且有效

UCXAML

<Grid>
        <StackPanel>
            <Button x:Name="elementoButton">
                <Image x:Name="elementoImage" Width="64" Height="64"/>
            </Button>
            <TextBlock x:Name="ipTextBlock" HorizontalAlignment="Center"/>
            <TextBlock x:Name="nomeTextBlock" HorizontalAlignment="Center"/>
        </StackPanel>
    </Grid>

UC C#

public Classes.Elementi elementi
        {
            get { return (Classes.Elementi)GetValue(elementiProperty); }
            set { SetValue(elementiProperty, value); }
        }

        // Using a DependencyProperty as the backing store for elementi.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty elementiProperty =
            DependencyProperty.Register("elementi", typeof(Classes.Elementi), typeof(ElementoControl), new PropertyMetadata(new Classes.Elementi { IndirizzoIP = "0.0.0.0", Nome = "Undefined", Image = "/Control Panel 2.0;component/img/default.png" }, SetElemento));



        private static void SetElemento(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ElementoControl elementoControl = new ElementoControl();
            if (elementoControl != null)
            {
            elementoControl.ipTextBlock.Text = (e.NewValue as Classes.Elementi).IndirizzoIP;
            elementoControl.nomeTextBlock.Text = (e.NewValue as Classes.Elementi).Nome;

            #region SetImage
            if ((e.NewValue as Classes.Elementi).Categoria == "Uruk")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Server")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Router")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Pannelli Solari")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "EasyCapture")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Computer")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Internet")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "Stampante")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            else if ((e.NewValue as Classes.Elementi).Categoria == "UPS")
            {
                elementoControl.elementoImage.Source = new BitmapImage(new Uri((e.NewValue as Classes.Elementi).Image, UriKind.Relative));
            }
            #endregion

            #region IsPingable
            if (IsPingable((e.NewValue as Classes.Elementi).IndirizzoIP))
            {
                elementoControl.elementoButton.Background = new SolidColorBrush(Colors.DarkGreen);
            }
            else
            {
                elementoControl.elementoButton.Background = new SolidColorBrush(Colors.DarkRed);
            }
            #endregion
            }
            else
               MessageBox.Show("usercontrol nullo");
        }

主窗口XAML

<StackPanel>
                <ListView x:Name="elementiListView" Background="DodgerBlue">
                    <ListView.ItemTemplate>
                        <DataTemplate>
                            <uc:ElementoControl elementi="{Binding}"/>
                            <!--<StackPanel>
                                <Button x:Name="elementoButton">
                                    <Image x:Name="imageButton" Source="{Binding Image}" Width="64" Height="64"></Image>
                                </Button>
                                <TextBlock Text="{Binding Nome}" HorizontalAlignment="Center"/>
                                <TextBlock Text="{Binding IndirizzoIP}" HorizontalAlignment="Center"/>
                            </StackPanel>-->
                        </DataTemplate>
                    </ListView.ItemTemplate>
                </ListView>
            </StackPanel>

主窗口 C#

private void ReadDatabase()
        {
            List<Classes.Elementi> elementi = new List<Classes.Elementi>();
            using (SQLiteConnection connection = new SQLiteConnection(App.ElementiDB()))
            {
                connection.CreateTable<Classes.Elementi>();
                elementi = connection.Table<Classes.Elementi>().ToList();
            }
            if (elementi != null)
            {
                    elementiListView.ItemsSource = elementi;
            }
        }

在 MainWindow XAML 中你可以看到我已经尝试过没有 uc，没有它它工作得很好但是我需要使用 uc，我希望要么使用 uc 我可以看到没有它也是一样

Answer 1

首先：DependencyObject d 是对刚刚设置了 elementi 属性的 ElementoControl 的引用。但是你忽略它。相反，您创建一个新的，在其上设置属性，然后丢弃新的。自然地，真正的控件没有显示其属性设置的迹象，因为您从未接触过它们。

private static void SetElemento(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    ElementoControl elementoControl = new ElementoControl();

    //  Why are you checking to see if this is null? You just created it. 
    if (elementoControl != null)
    {

改为这样做：

private static void SetElemento(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    //  If anybody calls this method with a reference to something other than 
    //  ElementoControl, that's a bug and an exception should be thrown. 
    if (!(d is ElementoControl))
    {
        throw new ArgumentException("d must be ElementoControl");
    }

    ElementoControl elementoControl = d as ElementoControl;

    //  This should be done mostly in XAML as well, but I don't have time at the 
    //  moment. I would give ElementoControl a boolean readonly dependency property 
    //  called IsPingable. I would set that property here, and in the XAML I would 
    //  give the button a Style with a DataTrigger that set the Button's background 
    //  color according to the value of IsPingable. 
    #region IsPingable
    if (IsPingable((e.NewValue as Classes.Elementi).IndirizzoIP))
    {
        elementoControl.elementoButton.Background = new SolidColorBrush(Colors.DarkGreen);
    }
    else
    {
        elementoControl.elementoButton.Background = new SolidColorBrush(Colors.DarkRed);
    }
    #endregion
}

其次：注意上面的方法我省略了大部分。那是因为您应该在 XAML 中绑定视图模型属性。另请注意，上述方法的绝大部分是一长串 if/else 分支，所有这些分支都做完全相同的事情。无论如何，你不需要决定十六种不同的方法来做同样的事情。去做就对了。

但这里真正的收获是您的 UserControl "inherits" 它的 DataContext 来自其父级，在本例中为 DataTemplate。出于这个原因，所有在原始 DataTemplate 中工作的绑定都必须在 UserControl 中以相同的方式工作（除非你通过将 UserControl 的 DataContext 显式设置为疯狂的东西来破坏事情，但从我在你的问题中看到的，你没有做那（如果你做了，不要））。 UserControls 被设计为以这种方式工作。

<Grid>
    <StackPanel>
        <Button x:Name="elementoButton">
            <Image Source="{Binding Image}" Width="64" Height="64"/>
        </Button>
        <TextBlock Text="{Binding IndirizzoIP}" HorizontalAlignment="Center"/>
        <TextBlock Text="{Binding Nome}" HorizontalAlignment="Center"/>
    </StackPanel>
</Grid>

UserControl 不显示数据

UserControl doesn't show the data

c#

data-binding

wpf

user-controls