Question

我试图从后面的代码创建一个具有与此相同属性的按钮：

<Button Content="Find Student" Tag="FindStudent" HorizontalAlignment="Right" x:Name="btnFindStudent" Click="btnGeneral_Click" />

代码背后：

            Button btnFindStudent = new Button();
            btnFindStudent.Click += this.btnGeneral_Click;
            btnFindStudent.Name = Convert.ToString("btnFindStudent");
            btnFindStudent.Tag = Convert.ToString("FindStudent");
            btnFindStudent.Content = Convert.ToString("View");
            btnFindStudent.HorizontalAlignment = HorizontalAlignment.Right;
            btnFindStudent.Height = 20;
            btnFindStudent.Width = 36;

问题是当我点击按钮时出现错误

Value cannot be null.
Parameter name: Children of 'System.Windows.Controls.UIElementCollection' cannot be null. Object derived from UIElement expected.

我不太确定丢失了什么，这是完整的代码：

public partial class FindStudent : UserControl
{
    private Dictionary<string, UserControl> _userControls = new Dictionary<string, UserControl>();
    public Dictionary<string, UserControl> GetUserControls()
    {
        return _userControls;
    }
    private static readonly Random rand = new Random();
    public FindStudent()
    {
        InitializeComponent();

        List<string> userControlKeys = new List<string>();
        userControlKeys.Add("FindStudent");
        Type type = this.GetType();
        Assembly assembly = type.Assembly;
        foreach (string userControlKey in userControlKeys)
        {
            string userControlFullName = String.Format("{0}.AppPages.{1}", type.Namespace, userControlKey);
            UserControl userControl = (UserControl)assembly.CreateInstance(userControlFullName);
            _userControls.Add(userControlKey, userControl);
        }
        for (int i = 1; i <= 10; i++)
        {
            Button btnFindStudent = new Button();
            btnFindStudent.Click += this.btnGeneral_Click;
            btnFindStudent.Name = Convert.ToString("btnFindStudent");
            btnFindStudent.Tag = Convert.ToString("FindStudent");
            btnFindStudent.Content = Convert.ToString("View {0}", i);
            btnFindStudent.HorizontalAlignment = HorizontalAlignment.Right;
            btnFindStudent.Height = 20;
            btnFindStudent.Width = 36;

            StackPanel stackPanel = new StackPanel();
            stackPanel.Children.Add(btnFindStudent);
            MainArea.Children.Add(stackPanel);
        }
    }
    private void btnGeneral_Click(object sender, RoutedEventArgs e)
    {
        PanelMainContent.Children.Clear();
        Button button = (Button)e.OriginalSource;
        Type type = this.GetType();
        Assembly assembly = type.Assembly;

        PanelMainContent.Children.Add(_userControls[button.Tag.ToString()]);
        // error on above line. 
    }
}

的Xaml：

<UserControl x:Class="WpfApplication4.AppPages.FindStudent"
             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" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <DockPanel HorizontalAlignment="Stretch" >
        <ScrollViewer VerticalScrollBarVisibility="Hidden">

            <DockPanel x:Name="PanelMainWrapper" Margin="10,20,0,0">
                <DockPanel x:Name="PanelMainContent" HorizontalAlignment="Stretch" VerticalAlignment="Top" Margin="0,30,0,0">
                    <ScrollViewer VerticalScrollBarVisibility="Hidden">
                        <WrapPanel x:Name="MainArea" VerticalAlignment="Bottom" HorizontalAlignment="Left">

                        </WrapPanel>
                    </ScrollViewer>
                </DockPanel>
            </DockPanel>

        </ScrollViewer>
    </DockPanel>
</UserControl>

它应该只是重新加载我正在使用的页面，我可以在以后设置appPage，但它不想玩球。 这可以在我的主窗口中工作，而不是我的控制但是我没有设置后面的代码按钮我使用我在主窗口中首次提到的xaml。这告诉我，我错过了按钮点击的东西（我认为设置正确），标签设置正确，但我不确定名称将是x：名称像我的xaml代码。

Answer 1

虽然你的代码真的让我感到困惑，但这里有什么不起作用。您可以通过

构建完全限定的类型名称

String.Format("{0}.AppPages.{1}", type.Namespace, userControlKey)

其中type.Namespace已经包含所讨论类型的完整命名空间，因此“AppPages”部分是不必要的。相反，你应该写

String.Format("{0}.{1}", type.Namespace, userControlKey)

为什么不简单地做

assembly.CreateInstance(type.FullName);

当你只想创建一个FindStudent的新实例时（我猜你想做什么）。

UIElementCollection不能为null。从UIElement派生的对象预计？

1 个答案: