wpf "{Binding Path=.}" 和 "{Binding}" 真的相等吗
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Are "{Binding Path=.}" and "{Binding}" really equal
提问by Fueled
In my WPF project, I have a ListBox that displays items from a List<string>collection. I wanted to make the text of these items editable, so I wrapped each of them in an ItemTemplate with a TextBox (might not be the best way, but I'm new to WPF). I was having trouble simply binding the TextBoxes' Text property to the value of each item. I finally stumbled upon an example using a single dot or period for its Path property ({Binding Path=.}):
在我的 WPF 项目中，我有一个 ListBox，用于显示List<string>集合中的项目。我想让这些项目的文本可编辑，所以我将它们每个都包裹在一个带有 TextBox 的 ItemTemplate 中（可能不是最好的方法，但我是 WPF 的新手）。我在简单地将 TextBoxes 的 Text 属性绑定到每个项目的值时遇到了麻烦。我终于偶然发现了一个使用单个点或句点作为其 Path 属性 ( {Binding Path=.})的示例：
<ListBox ItemsSource="{Binding ElementName=recipesListbox,Path=SelectedItem.Steps}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Path=.}"/>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
However I don't understand why simply using {Binding}didn't work.
但是我不明白为什么简单地使用{Binding}不起作用。
It raised a "Two-way binding requires Path or XPath" exception, as according to Microsoft:
根据 Microsoft 的说法，它引发了“双向绑定需要 Path 或 XPath”异常：
[...] a period (.) path can be used to bind to the current source. For example, Text="{Binding}" is equivalent to Text="{Binding Path=.}"
[...] 句点 (.) 路径可用于绑定到当前源。例如，Text="{Binding}" 等价于 Text="{Binding Path=.}"
Could someone shed light on this ambiguous behavior?
有人可以解释这种模棱两可的行为吗？
EDIT:Moreover, it seems {Binding Path=.}does not necessarily give two-way binding, as modifying the text and moving the focus does not update the underlying source (the same source has also properties displayed and successfully modified on a DataGrid control). I'm definitely missing something here.
编辑：此外，似乎{Binding Path=.}不一定要提供双向绑定，因为修改文本和移动焦点不会更新底层源（同一源也有在 DataGrid 控件上显示和成功修改的属性）。我肯定在这里遗漏了一些东西。
回答by H.B.
The point of the exception presumably is that you cannot two-way bind a binding-source itself, so it tries to prevent you from creating a binding which does not behave the way you would want it to. By using {Binding Path=.}you just trick the error handling.
例外的一点大概是你不能双向绑定绑定源本身，所以它试图阻止你创建一个行为不符合你希望的绑定。通过使用{Binding Path=.}你只是欺骗错误处理。
(Also it's not unheard of that documentation is erroneous or inaccurate, though i do like the MSDN documentation a lot in general as it usually does contain the crucial points one is interested in)
（此外，该文档是错误或不准确的并不是闻所未闻，尽管我确实非常喜欢 MSDN 文档，因为它通常包含人们感兴趣的关键点）
回答by ceyko
The documentation states that {Binding}is equivalent to {Binding Path=.}. However it is notequivalent to {Binding Path}as you have typed. If you include the Pathproperty, you must assign it to something, be it Path=.or Path=OtherProperty.
文档说明这{Binding}等效于{Binding Path=.}. 但是，它不等同于{Binding Path}您键入的内容。如果您包含该Path属性，则必须将其分配给某物，无论是 itPath=.还是Path=OtherProperty。
回答by ceyko
These are not the same. If you bind this where ConsoleMessages is an ObservableCollection string with just {Binding} you get a "Two-way binding requires Path or XPath." exception where as {Binding Path=.} works. This is with WPF 4.0...
这些是不一样的。如果在 ConsoleMessages 是一个 ObservableCollection 字符串的地方绑定它，只有 {Binding} 你会得到一个“双向绑定需要 Path 或 XPath”。{Binding Path=.} 工作的异常。这是 WPF 4.0 ...
<ItemsControl x:Name="ConsoleOutput" ItemsSource="{Binding ConsoleMessages, Mode=OneWay}" MaxHeight="400">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Path=.}" BorderThickness="0" Margin="0" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
My 2p worth...
我的 2p 值...
回答by Vwake
In short, the difference between the two is analogous with the difference between the traditional pass by value and pass by reference. (FYR - What's the difference between passing by reference vs. passing by value?)
简而言之，两者的区别类似于传统的传值和传引用的区别。（FYR -按引用传递与按值传递有什么区别？）
However I don't understand why simply using {Binding} didn't work (it raised a "Two-way binding requires Path or XPath" exception)
但是我不明白为什么简单地使用 {Binding} 不起作用（它引发了“双向绑定需要 Path 或 XPath”异常）
Lets assume here for now that {Binding}can be used for two way binding. In general {Binding}creates a value based link with datacontext which does not allow updating the datacontext.
现在让我们假设它{Binding}可用于双向绑定。通常{Binding}，使用不允许更新数据上下文的数据上下文创建基于值的链接。
Whereas {Binding Path=.}creates reference based link with the memory area referenced by the 'Path' which allows updating the value through reference.(in this case 'dot' the current datacontext).
而{Binding Path=.}使用“路径”引用的内存区域创建基于引用的链接，这允许通过引用更新值。（在这种情况下，“点”当前数据上下文）。
Hope this helps!
希望这可以帮助！
