c# – 在构造函数中设置DataContext = this和在WPF中绑定到{RelativeSource Self}之间的区别？

下一代码按预期工作：

AskWindow.xaml：

<Window
    x:Class='AskWPF.AskWindow'
    xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
    xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'
    >

<DataGrid ItemsSource="{Binding SimpleItems}" />

</Window>

AskWindow.xaml.cs：

namespace AskWPF {

public class SimpleRow {
    private string firstColumn;
    private string secondColumn;

    public SimpleRow(string first, string second) {
        firstColumn = first;
        secondColumn = second;
    }

    public string FirstColumn {
        get { return firstColumn; }
        set { firstColumn = value; }
    }

    public string SecondColumn {
        get { return secondColumn; }
        set { secondColumn = value; }
    }
}

public partial class AskWindow : Window {

    private ObservableCollection<SimpleRow> simpleItems;

    public AskWindow() {
        InitializeComponent();
        DataContext = this;

        simpleItems = new ObservableCollection<SimpleRow>();
        simpleItems.Add(new SimpleRow("row 0, column 0", "row 0, column 1"));
        simpleItems.Add(new SimpleRow("row 1, column 0", "row 1, column 1"));
    }

    public ObservableCollection<SimpleRow> SimpleItems {
        get { return simpleItems; }
    }
}

}

但是如果在Window标签和注释行DataContext =中设置DataContext ='{Binding RelativeSource = {RelativeSource Self}}’,我们会得到一个空窗口.为什么？

AskWindow.xaml：

<Window .... DataContext='{Binding RelativeSource={RelativeSource Self}}'>

    <DataGrid ItemsSource="{Binding SimpleItems}" />

</Window>

AskWindow.xaml.cs：

...
public AskWindow() {
    InitializeComponent();
    // DataContext = this;

    simpleItems = new ObservableCollection<SimpleRow>();
    simpleItems.Add(new SimpleRow("row 0, column 0", "row 0, column 1"));
    simpleItems.Add(new SimpleRow("row 1, column 0", "row 1, column 1"));
}
...

解决方法:

这是我的猜测.在这两种情况下,您的Collection都是空的.确切地说,在InitializeComponent之后.此时,初始数据绑定获取数据,但没有datacontext.现在,通过设置DataContext,您的属性将被引发,并且与之相关的每个绑定都会失效并刷新.这是我的猜测部分,它的工作原理是延迟了对ItemsSource的绑定,因此它只是在下一行设置集合.

简而言之：设置Datacontext将重新绑定绑定.但是在您的RelativeSource示例中,您的绑定从一开始就起作用,但该集合为null,您从未告诉wpf重新绑定绑定.
如果你直接初始化你的收藏它应该工作正常.

标签：c,wpf,xaml,datacontext,relativesource
来源： https://codeday.me/bug/20190703/1368094.html