XAML:更改DataContext时的更新绑定

Question

我有一个简单的XAML文件，它包含一个标签，其前台属性包含绑定：

<Grid xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" Width="200" Height="100" >
    <Label Content="Sampletext" Foreground="{Binding Path=Color}" />
</Grid>

当我加载模板并应用DataContext时，前台仍然具有默认值。在不使用渲染网格的情况下，可以获得绑定的前景值吗？

// Load template
string templatePath = "/WpfApplication1;component/Template.xaml";
Grid grid = Application.LoadComponent(new Uri(templatePath, UriKind.Relative)) as Grid;

// Set dataContext
grid.DataContext = new { Color = Brushes.Green };

// Foregound still has default value
var foreground = ((Label)grid.Children[0]).Foreground;

项目可在以下位置下载：http://dl.dropbox.com/u/21096596/WpfApplication1.zip

Answer 1

试一试

lblName.GetBindingExpression(Label.ForegroundProperty).UpdateTarget();

在此之前

var foreground = ((Label)grid.Children[0]).Foreground;

Answer 2

有自动的DataContext更改通知，如果满足必要的条件，绑定将更新。其中之一是加载了控件(IsLoaded == true)，这在代码中不是这样的。只有在将控件添加到UI的某个位置时，该控件才会加载。

示例测试代码：

private void Button_Click(object sender, RoutedEventArgs e)
{
    Grid grid = null;
    Action action = () =>
        {
            var foreground = ((Label)grid.Children[0]).Foreground;
            MessageBox.Show(foreground.ToString());

            grid.DataContext = new { Color = Brushes.Green };

            foreground = ((Label)grid.Children[0]).Foreground;
            MessageBox.Show(foreground.ToString());
        };
    grid = Application.LoadComponent(new Uri("Stuff/GridOne.xaml", UriKind.Relative)) as Grid;
    if (grid.IsLoaded)
    {
        action();
    }
    else
    {
        grid.Loaded += (s, _) => action();
    }
    // This adds the grid to some StackPanel, if you do not do something like this
    // nothing will happen since the control will not be loaded and thus the event
    // will not fire, etc. 
    ControlStack.Children.Add(grid);
}

Answer 3

为什么你需要一次绑定？把它移开，它就能工作了。