ListView、UserControl、DependencyProperty、ObservableCollection、INotifyPropertyChanged 的​​绑定错误

Question

我的绑定不起作用。我搜索了错误，但我不明白如何在我的情况下修复它。

System.Windows.Data 错误：1：无法创建默认转换器以在类型“MyApplication.MyUserControl”和“MyApplication.Person”之间执行“单向”转换。考虑使用 Binding 的 Converter 属性。绑定表达式：路径=； DataItem='MyUserControl' (Name='');目标元素是'MyUserControl'（名称=''）；目标属性是“PersonInfo”（类型“Person”）

System.Windows.Data 错误：5：BindingExpression 生成的值对目标属性无效。； Value='MyApplication.MyUserControl' BindingExpression:Path=; DataItem='MyUserControl' (Name='');目标元素是'MyUserControl'（名称=''）；目标属性是“PersonInfo”（类型“Person”）

基本上它是一个绑定到 Person 类的 ObservableCollection 的 ListView。

MainWindow.xaml.cs

public partial class MainWindow : Window
{
    public ObservableCollection<Person> PersonCollection { set; get; }

    public MainWindow()
    {
        PersonCollection = new ObservableCollection<Person>();
        InitializeComponent();
        PersonCollection.Add(new Person() { Name = "Bob", Age = 20 });
    }
}

MainWindow.xaml

<Window DataContext="{Binding RelativeSource={RelativeSource Self}}" xmlns:self="clr-namespace:MyApplication" x:Class="MyApplication.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<ListView ItemsSource="{Binding PersonCollection}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <StackPanel>
                <self:MyUserControl PersonInfo="{Binding}" />
            </StackPanel>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>
</Window>

MyUserControl.xaml.cs

public partial class MyUserControl : UserControl
{
    public static readonly DependencyProperty PersonProperty = DependencyProperty.Register("PersonInfo", typeof(Person), typeof(MyUserControl));

    public Person PersonInfo
    {
        get { return (Person)GetValue(PersonProperty); }
        set { SetValue(PersonProperty, value); }
    }

    public MyUserControl()
    {
        InitializeComponent();
    }
}

MyUserControl.xaml

<UserControl DataContext="{Binding RelativeSource={RelativeSource Self}}" x:Class="MyApplication.MyUserControl" 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">
<TextBlock Text="{Binding PersonInfo.Name}" />
</UserControl>

Person.cs

public class Person : INotifyPropertyChanged
{
    public int Age { set; get; }
    public string Name { set; get; }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(info));
    }
}

Answer 1

我不太明白你为什么要把它弄得那么复杂。您可以在没有 PersonInfo 属性且不修改其 DataContext 的情况下轻松绑定您的 UserControl。

<UserControl x:Class="MyApplication.MyUserControl" 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"> 
    <TextBlock Text="{Binding Name}" /> 
</UserControl>

然后将 UserControl 放置在 DataTemplate 中，无需显式绑定。它的 DataContext 将已经包含一个 Person 对象。

<DataTemplate>      
    <StackPanel>      
        <self:MyUserControl />      
    </StackPanel>      
</DataTemplate>      

Answer 2

虽然您解决了问题，但您的整个 Binding 代码对我来说似乎是错误的，所以我提出了这个替代方案：

拥有所有绑定源对象的基类 - ObservableObject.cs

public abstract class ObservableObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = this.PropertyChanged;
        if (handler != null)
            handler(this, e);
    }

    protected void SetValue<T>(ref T field, T value, string propertyName)
    {
        if (!EqualityComparer<T>.Default.Equals(field, value))
        {
            field = value;
            this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
        }
    }
}

为您的 MainWindow 提供一个视图模型 - MainWindowModel.cs

public class MainWindowModel : ObservableObject
{
    private readonly ObservableCollection<Person> personCollection = new ObservableCollection<Person>()
    {
        new Person() { Name = "Bob", Age = 20 }
    };

    public ObservableCollection<Person> PersonCollection
    {
        get { return this.personCollection; }
    }
}

MainWindow.xaml.cs 现在基本上是空的。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
}

MainWindow.xaml 将 DataContext 设置为新的 MainWindowModel 实例。

<Window x:Class="MyApplication.MainWindow" 
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:self="clr-namespace:MyApplication">
    <Window.DataContext>
        <self:MainWindowModel/>
    </Window.DataContext>
    <ListView ItemsSource="{Binding PersonCollection}">
        <ListView.ItemTemplate>
            <DataTemplate>
                <StackPanel>
                    <self:MyUserControl/>
                </StackPanel>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</Window>

MyUserControl.xaml.cs 也基本上是空的（仅包含自动生成的代码）。

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

MyUserControl.xaml

<UserControl x:Class="MyApplication.MyUserControl" 
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <TextBlock Text="{Binding Name}"/>
</UserControl>

Person.cs

public class Person : ObservableObject
{
    private int age;
    private string name;

    public int Age
    {
        get { return this.age; }
        set { this.SetValue(ref this.age, value, "Age"); }
    }

    public string Name
    {
        get { return this.name; }
        set { this.SetValue(ref this.name, value, "Name"); }
    }
}

Answer 3

将您的 UserControl XAML 更改为

<UserControl x:Class="MyApplication.MyUserControl"
             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">
    <TextBlock DataContext="{Binding RelativeSource={RelativeSource AncestorType=UserControl}}"
               Text="{Binding PersonInfo.Name}" />
</UserControl>

这里是 good explanation，用于解决 DataContext 的问题。