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DataTemplate的绑定为目标提供了不正确的/unset/null值

datatemplate wpf c#

wondra · 技术社区 · 6 年前

我想传播 DataContext 从动态创建的 DataTemplate 在一个 ContentControl 比如下面一个:

var myFactory = new FrameworkElementFactory(controlTypeToDisplay);//= typeof(MyControl)
var dctxBinding = new Binding
{
    Path = new PropertyPath("DataContext.Dctx"),
    Mode = BindingMode.OneWayToSource,
    RelativeSource = new RelativeSource(RelativeSourceMode.FindAncestor, typeof(ContentControl), 1)
};
myFactory.SetBinding(FrameworkElement.DataContextProperty, dctxBinding);

return new DataTemplate() { VisualTree = myFactory };

然而,这种约束的结果是 null 即使DataContext是在 MyControl 的构造函数。MyControl的DataContext肯定不会再设置为null,构造函数是在 Dctx .我怎样才能把装订好 我的控制 的DataContext和 Dctx 属性总是同步的吗?

问题的完整示例(如果工作正常,应显示两个“FooBar”文本块):

//MyControl.xaml
<Grid>
    <TextBlock Text="{Binding}"/>
</Grid>
//MyControl.xaml.cs
public MyControl()
{
    InitializeComponent();
    DataContext = "FooBar";
    this.DataContextChanged += MyControl_DataContextChanged;
}

private void MyControl_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    MessageBox.Show("An unexpected change");
}

//MainWindow.xaml
<StackPanel>
    <ContentControl ContentTemplate="{Binding DataTemplate}"/>
    <TextBlock Text="{Binding Dctx, TargetNullValue='&lt;null&gt;'}" />
</StackPanel>

//MainWindow.xaml.cs
public partial class MainWindow : Window, INotifyPropertyChanged
{
    private Type controlTypeToDisplay = typeof(MyControl);
    public DataTemplate DataTemplate
    { get {/*see first listing*/ } }

    private object _dctx;
    public object Dctx
    {
        get { return _dctx; }
        set { _dctx = value; RaisePropertyChanged(); }
    }

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged([CallerMemberName]string caller = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(caller));
    }
}

1 回复 | 直到 6 年前

mm8 6 年前

这个 DataContext 中的根元素的 ContentTemplate 一个 ContentControl 是吗 内容控制 是的 Content .绑好绳子 所容纳之物 财产归你所有 数据上下文 :

<ContentControl Content="{Binding Dctx}" ContentTemplate="{Binding DataTemplate}"/>

您还必须设置 数据上下文 关于 内容控制 自身(或父窗口)的某个位置,并向 DataTemplate :

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public DataTemplate DataTemplate
    {
        get {
            var myFactory = new FrameworkElementFactory(typeof(TextBlock));
            myFactory.SetBinding(TextBlock.TextProperty, new Binding(".")); //bind to the DataContext
            return new DataTemplate() { VisualTree = myFactory };
        }
    }

    private object _dctx = new object(); //set the Dxtc property somewhere
    public object Dctx
    {
        get { return _dctx; }
        set { _dctx = value; RaisePropertyChanged(); }
    }

    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged([CallerMemberName]string caller = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(caller));
    }

}