UWP：替换数据绑定

Question

我有一个非常奇怪的问题。如果我设置了绑定并将绑定更改为另一个属性，它将不起作用。

看这个简单的例子

lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("Subtotal"), Source = Order, Mode = BindingMode.OneWay });
lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("FinalTotal"), Source = Order, Mode = BindingMode.OneWay });

当FinalTotal改变时， lblTotal 文本不会改变。

现在，注释掉第一行。

//lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("Subtotal"), Source = Order, Mode = BindingMode.OneWay });
lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("FinalTotal"), Source = Order, Mode = BindingMode.OneWay });

现在它起作用了！！！！更改FinalTotal将更改 lblTotal 文本！知道为什么吗？

此外，BindingOperations.ClearBinding()在 UWP 中不可用。所以我试图用空绑定替换它，但它仍然不起作用。

lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("Subtotal"), Source = Order, Mode = BindingMode.OneWay });

//remove binding - not sure if this is correct way to remove binding because
//BindingOperations.ClearBinding() isn't available in UWP!
BindingOperations.SetBinding(lblTotal, TextBlock.TextProperty, new Binding());

lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("FinalTotal"), Source = Order, Mode = BindingMode.OneWay });

我的问题是： 1. 如何更换UWP中的绑定？2. 如何移除 UWP 中现有的绑定（即等效于BindingOperations.ClearBinding() 的功能）？

谢谢你的帮助...

Answer 1

正如它在FrameworkElement.SetBinding 方法中声明的那样：

注意 调用SetBinding方法并传入新的Binding对象不一定会删除现有绑定。相反，您应该首先调用DependencyObject.ClearValue方法，然后调用SetBinding。

所以你可以改变你的代码，如下所示：

lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("Subtotal"), Source = Order, Mode = BindingMode.OneWay });
lblTotal.ClearValue(TextBlock.TextProperty);
lblTotal.SetBinding(TextBlock.TextProperty, new Binding() { Path = new PropertyPath("FinalTotal"), Source = Order, Mode = BindingMode.OneWay });

在此之后，您的代码应该能够工作。欲了解更多信息，请参见备注的FrameworkElement.SetBinding也BindingOperations.SetBinding。