在代码后面访问silverlight用户控件的公共属性

Question

我创建了一个简单的Silverlight用户控件，并定义了一个公共属性AllowMultiple。

public bool AllowMultiple { get; set; }

现在，我将XAML中的这个公共属性设置为：

<Controls1:PeopleChooser Name="SinglePeopleChooser" AllowMultiple="False" Width="Auto" d:LayoutOverrides="Height"/>
<Controls1:PeopleChooser Name="MultiplePeopleChooser" AllowMultiple="True" Width="Auto" d:LayoutOverrides="Height"/>

我想知道，这是我能得到这个公共财产价值的最好的事件。我试图在构造函数中获取这个值，并试图在我的用户控件中隐藏/显示一些控件，但它不起作用。

public PeopleChooser()
{
    InitializeComponent();            

    if (AllowMultiple)
    {
        UsersListBox.Visibility = System.Windows.Visibility.Visible;
        UserTextBox.Visibility = System.Windows.Visibility.Collapsed;
        ResolveButton.Visibility = Visibility.Collapsed;               
    }
    else
    {
        UsersListBox.Visibility = System.Windows.Visibility.Collapsed;
        UserTextBox.Visibility = System.Windows.Visibility.Visible;
        ResolveButton.Visibility = Visibility.Visible;
    }

}

可能是因为在构造函数初始化期间，这个公共属性的值没有由框架分配给对象。

Answer 1

我可以通过加载事件来解决这个问题。不需要依赖项属性。请看下面的代码。我可以在Loaded事件中成功地访问属性值。

 public PeopleChooser()
        {

            this.Loaded += PeopleChooser_Loaded;
            InitializeComponent();                     

        }


  void PeopleChooser_Loaded(object sender, RoutedEventArgs e)
        {
            if (AllowMultiple)
            {
                UsersListBox.Visibility = System.Windows.Visibility.Visible;
                UserTextBox.Visibility = System.Windows.Visibility.Collapsed;
                ResolveButton.Visibility = Visibility.Collapsed;            

            }
            else
            {
                UsersListBox.Visibility = System.Windows.Visibility.Collapsed;
                UserTextBox.Visibility = System.Windows.Visibility.Visible;
                ResolveButton.Visibility = Visibility.Visible;
            }

Answer 2

用一个后场转换公共属性，

    private bool _allowMultiple;
    public bool AllowMultiple
    {
        get { return _allowMultiple; }
        set { _allowMultiple = value; }
    }

在setter中放置一个断点，并检查它是否击中了Constructor，如果没有，您可以使用Loaded事件进行检查并使用该事件。

Answer 3

如果使用依赖项属性，则可以将其他元素属性绑定到人员选择器的AllowMultiple属性，并使用可见性转换器显示/隐藏这些属性。示例：

public partial class PeopleChooser : UserControl
{
    public PeopleChooser()
    {
        InitializeComponent();
    }

    public static readonly DependencyProperty AllowMultipleProperty = DependencyProperty.Register("AllowMultiple", typeof(bool), typeof(PeopleChooser), null);
    public bool AllowMultiple
    {
        get { return (bool)GetValue(AllowMultipleProperty); }
        set { SetValue(AllowMultipleProperty, value); }
    }
}

<UserControl x:Class="TestSilverlightApplication.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400"
    xmlns:lcl="clr-namespace:TestSilverlightApplication">
    <UserControl.Resources>
        <lcl:VisibilityConverter x:Key="VisibilityConverter" />
    </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White">
        <StackPanel Orientation="Vertical">
            <Button Click="Button_Click" Content="Toggle allow multiple" />
            <lcl:PeopleChooser x:Name="lclPeopleChooser" AllowMultiple="False"></lcl:PeopleChooser>
            <TextBlock Text="Dependent content" Visibility="{Binding AllowMultiple, ElementName=lclPeopleChooser, Converter={StaticResource VisibilityConverter}}" />
        </StackPanel>

    </Grid>
</UserControl>

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        lclPeopleChooser.AllowMultiple = !lclPeopleChooser.AllowMultiple;
    }

public class VisibilityConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        bool parsedValue = false;
        bool.TryParse(value.ToString(), out parsedValue);
        if (parsedValue)
        {
            return Visibility.Visible;
        }
        return Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

通过这种方式，您可以避免页面事件，并可能将AllowMultiple属性绑定到视图模型属性，并让UI自行处理。