In WPF, what are the differences between the x:Name and Name attributes?
.NetWpfXamlName Attribute.Net Problem Overview
Sometimes it seems that the Name
and x:Name
attributes are interchangeable.
So, what are the definitive differences between them, and when is it preferable to use one over the other?
Are there any performance or memory implications to using them the wrong way?
.Net Solutions
Solution 1 - .Net
There really is only one name in XAML, the x:Name
. A framework, such as WPF, can optionally map one of its properties to XAML's x:Name
by using the RuntimeNamePropertyAttribute
on the class that designates one of the classes properties as mapping to the x:Name attribute of XAML.
The reason this was done was to allow for frameworks that already have a concept of "Name" at runtime, such as WPF. In WPF, for example, FrameworkElement
introduces a Name property.
In general, a class does not need to store the name for x:Name
to be useable. All x:Name
means to XAML is generate a field to store the value in the code behind class. What the runtime does with that mapping is framework dependent.
So, why are there two ways to do the same thing? The simple answer is because there are two concepts mapped onto one property. WPF wants the name of an element preserved at runtime (which is usable through Bind, among other things) and XAML needs to know what elements you want to be accessible by fields in the code behind class. WPF ties these two together by marking the Name property as an alias of x:Name.
In the future, XAML will have more uses for x:Name, such as allowing you to set properties by referring to other objects by name, but in 3.5 and prior, it is only used to create fields.
Whether you should use one or the other is really a style question, not a technical one. I will leave that to others for a recommendation.
See also AutomationProperties.Name VS x:Name, AutomationProperties.Name is used by accessibility tools and some testing tools.
Solution 2 - .Net
They are not the same thing.
x:Name
is a xaml concept, used mainly to reference elements. When you give an element the x:Name xaml attribute, "the specified x:Name
becomes the name of a field that is created in the underlying code when xaml is processed, and that field holds a reference to the object." (MSDN) So, it's a designer-generated field, which has internal access by default.
Name
is the existing string property of a FrameworkElement
, listed as any other wpf element property in the form of a xaml attribute.
As a consequence, this also means x:Name
can be used on a wider range of objects. This is a technique to enable anything in xaml to be referenced by a given name.
Solution 3 - .Net
x:Name and Name are referencing different namespaces.
x:name is a reference to the x namespace defined by default at the top of the Xaml file.
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Just saying Name uses the default below namespace.
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
x:Name is saying use the namespace that has the x alias. x is the default and most people leave it but you can change it to whatever you like
xmlns:foo="http://schemas.microsoft.com/winfx/2006/xaml"
so your reference would be foo:name
Define and Use Namespaces in WPF
OK lets look at this a different way. Say you drag and drop an button onto your Xaml page. You can reference this 2 ways x:name and name. All xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"; and xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"; are is references to multiple namespaces. Since xaml holds the Control namespace(not 100% on that) and presentation holds the FrameworkElement AND the Button class has a inheritance pattern of:
Button : ButtonBase
ButtonBase : ContentControl, ICommandSource
ContentControl : Control, IAddChild
Control : FrameworkElement
FrameworkElement : UIElement, IFrameworkInputElement,
IInputElement, ISupportInitialize, IHaveResources
So as one would expect anything that inherits from FrameworkElement would have access to all its public attributes. so in the case of Button it is getting its Name attribute from FrameworkElement, at the very top of the hierarchy tree. So you can say x:Name or Name and they will both be accessing the getter/setter from the FrameworkElement.
WPF defines a CLR attribute that is consumed by XAML processors in order to map multiple CLR namespaces to a single XML namespace. The XmlnsDefinitionAttribute attribute is placed at the assembly level in the source code that produces the assembly. The WPF assembly source code uses this attribute to map the various common namespaces, such as System.Windows and System.Windows.Controls, to the http://schemas.microsoft.com/winfx/2006/xaml/presentation namespace.
So the assembly attributes will look something like:
PresentationFramework.dll - XmlnsDefinitionAttribute:
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows")]
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows.Data")]
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows.Navigation")]
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows.Shapes")]
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows.Documents")]
[assembly: XmlnsDefinition("http://schemas.microsoft.com/winfx/2006/xaml/presentation", "System.Windows.Controls")]
Solution 4 - .Net
They're both the same thing, a lot of framework elements expose a name property themselves, but for those that don't you can use x:name - I usually just stick with x:name because it works for everything.
Controls can expose name themselves as a Dependency Property if they want to (because they need to use that Dependency Property internally), or they can choose not to.
More details in msdn here and here:
> Some WPF framework-level applications > might be able to avoid any use of the > x:Name attribute, because the Name > dependency property as specified > within the WPF namespace for several > of the important base classes such as > FrameworkElement/FrameworkContentElement > satisfies this same purpose. There are > still some common XAML and framework > scenarios where code access to an > element with no Name property is > necessary, most notably in certain > animation and storyboard support > classes. For instance, you should > specify x:Name on timelines and > transforms created in XAML, if you > intend to reference them from code. > > If Name is available as a property on > the class, Name and x:Name can be used > interchangeably as attributes, but an > error will result if both are > specified on the same element.
Solution 5 - .Net
X:Name can cause memory issues if you have custom controls. It will keep a memory location for the NameScope entry.
I say never use x:Name unless you have to.
Solution 6 - .Net
Name:
- can be used only for descendants of FrameworkElement and FrameworkContentElement;
- can be set from code-behind via SetValue() and property-like.
x:Name:
- can be used for almost all XAML elements;
- can NOT be set from code-behind via SetValue(); it can only be set using attribute syntax on objects because it is a directive.
Using both directives in XAML for one FrameworkElement or FrameworkContentElement will cause an exception: if the XAML is markup compiled, the exception will occur on the markup compile, otherwise it occurs on load.
Solution 7 - .Net
The only difference is that if you are using user Controls into a control from Same Assembly then Name will not identify your control and you will get an error " Use x:Name for controls in the same Assembly". So x:Name is the WPF versioning of naming controls in WPF. Name is just used as a Winform Legacy. They wanted to differentiate the naming of controls in WPF and winforms as they use attributes in Xaml to identify controls from other assemblies they used x: for Names of control.
Just keep in mind dont put a name for a control just for the sake of keeping it as it resides in memory as a blank and it will give you a warning that Name has been applied for a control buts its never used.
Solution 8 - .Net
x:Name
means: create a field in the code behind to hold a reference to this object.
Name
means: set the name property of this object.
Solution 9 - .Net
I always use the x:Name variant. I have no idea if this affects any performance, I just find it easier for the following reason. If you have your own usercontrols that reside in another assembly just the "Name" property won't always suffice. This makes it easier to just stick too the x:Name property.
Solution 10 - .Net
It's not a WPF item but a standard XML one and BtBh has correctly answered it, x refers to the default namespace. In XML when you do not prefix an element/attribute with a namespace it assumes you want the default namespace.
So typing just Name
is nothing more than a short hand for x:Name
. More details on XML namespaces can be found at link text
Solution 11 - .Net
The specified x:Name becomes the name of a field that is created in the underlying code when XAML is processed, and that field holds a reference to the object. In Silverlight, using the managed API, the process of creating this field is performed by the MSBuild target steps, which also are responsible for joining the partial classes for a XAML file and its code-behind. This behavior is not necessarily XAML-language specified; it is the particular implementation that Silverlight applies to use x:Name in its programming and application models.
Solution 12 - .Net
When you declare a Button element in XAML you are referring to a class defined in windows run time called Button.
Button has many attribute such as background, text, margin, ..... and an attribute called Name.
Now when you declare a Button in XAML is like creating an anonymous object that happened to have an attribute called Name.
In general you can not refer to an anonymous object, but in WPF framework XAML processor enables you to refer to that object by whatever value you have given to Name attribute.
So far so good.
Another way to create an object is create a named object instead of anonymous object. In this case XAML namespace has an attribute for an object called Name (and since it is in XAML name space thus have X:) that you may set so you can identify your object and refer to it.
Conclusion:
Name is an attribute of a specific object, but X:Name is one attribute of that object (there is a class that defines a general object).
Solution 13 - .Net
One of the answers is that x:name is to be used inside different program languages such as c# and name is to be used for the framework. Honestly that is what it sounds like to me.
Solution 14 - .Net
Name
can also be set using property element syntax with inner text, but that is uncommon. In contrast, x:Name
cannot be set in XAML
property element syntax, or in code using SetValue
; it can only be set using attribute syntax on objects because it is a directive.
If Name
is available as a property on the class, Name
and x:Name
can be used interchangeably as attributes, but a parse exception will result if both are specified on the same element. If the XAML is markup compiled, the exception will occur on the markup compile, otherwise it occurs on load.
Solution 15 - .Net
My research is x:Name
as global variable. However, Name
as local variable. Does that mean x:Name you can call it anywhere in your XAML file but Name is not.
Example:
<StackPanel>
<TextBlock Text="{Binding Path=Content, ElementName=btn}" />
<Button Content="Example" Name="btn" />
</StackPanel>
<TextBlock Text="{Binding Path=Content, ElementName=btn}" />
You can't Binding
property Content
of Button
with Name is "btn" because it outside StackPanel