In WPF, what are the differences between the x:Name and Name attributes?

Question

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?

Girardo

Responses suggest that using x:Name all the time works fine. I've just had to change it to Name otherwise I couldn't reference the control in my .xaml.cs code so I'm going to assume that it is no longer the case that it works fine all the time. – Apps

Answer 1

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.

Incandesce

In Visual Studio 2010 the Name property is set (not x:Name) when you edit the XAML via the designer. It appears as if MS encourages the use of Name over x:Name so I guess that is the defacto standard. – Spastic

I don't think the two are interchangeable in general. Naming user controls require x:Name because Name would not create a field to be recognized in code-behind. I still don't know why this happens, though. – Bison

They are not nor did I mean to imply they did. In WPF, if an element has a Name property it they mean the same thing. If the element doesn't have a Name property, you must use x:Name. – Incandesce

@Bison Today it absolutely makes not difference whether you use Name or x:Name for any type that derives from FrameworkElement (which includes most types you'd use in XAML including UserControl, a member will be generated correctly in any case). This is because FrameworkElement is decorated with [RuntimeNameProperty("Name")]. – Sherly

Answer 2

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.

Ranson

So why can either Name or x:Name be used with Binding.ElementName? It seems that the x:Name attribute is not only used to name a field in generated code, but that it's also available in metadata at runtime. – Girardo

It is a generated field like the field Name in the Design properties of the WinForms editor. There you place a name in the property list and it becomes the name of a field. This is the same behaviour. Of course it is available at runtime since it is an internal field compiled into the code behind. Binding.ElementName checks for either case, that is the xaml editor "magic", the x:Name is not magical in itself. – Ranson

A field will be generated no matter whether you use x:Name or Name. There is no difference between x:Name and Name for all types derived from FrameworkElement (which most types you'd you in XAML are) with one single exception: If you want to give a UserControl a name and that UserControl is declared in the same assembly where you also want to use it you'll have to use x:Name because limitation of the XAML parser. – Sherly

Answer 3

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.

MSDN Reference

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")]  

Florentinoflorenza

I don't think it's true that http://schemas.microsoft.com/winfx/2006/xaml holds Control since you can use it directly in XAML without an 'x' namespace: <Control /> – Girardo

Answer 4

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 the Microsoft documentation 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.

Jens

If there's no difference, then why would there be two ways of doing the same thing? Both ways existed in the first release of WPF. – Girardo

@Steve, I didn't downvote any of the answers on this question, even though none of them so far have been very appropriate. – Girardo

I don't see how an answer that not only gives you the answer, but also gives you links to MSDN for a more information on the topic isn't appropriate? :-) – Jens

@Steve your original answer did not address my question, hence my comment. I'm not looking for blind-faith "do it this way", but rather an insightful answer that explained why two ways exist, even if one of them does work all the time. Technically correct != Appropriate. Your update is much better. – Girardo

Much the same answer here: wpfwiki.com/WPF%20Q16.4.ashx x:Name are giving the control a name to use in code-behind. Some classes will provide a Name-property for the same purpose. For these classes, there is no difference between x:name and name. – Minier

Answer 5

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.

Wynn

Agreed. Worked on a kiosk app which had numerous memory leaks and the prior dev team's resolution was just to force a reboot. Much of the leaks were easily identified. Yet, after fixing those found via IntelliTrace and JustTrace, some refs still eluded implicit and explicit garbage collection. I read: support.scichart.com/index.php?/News/NewsItem/View/21/… Found that reducing x:Name further improved performance. – Lamppost

It it my understanding this affects both Name and x:Name as both are added to NameScope. If you need a Name on your element, there's no getting around it. You can repro in code on an element with no name via FrameworkElement.RegisterName("elementname"). However, if you call FrameworkElement.UnregisterName("elementname") it can be "dereferenced". – Bounty

Answer 6

Name:

1. can be used only for descendants of FrameworkElement and FrameworkContentElement;
2. can be set from code-behind via SetValue() and property-like.

x:Name:

1. can be used for almost all XAML elements;
2. 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.

Bushelman

Answer 7

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.

Electrophorus

Answer 8

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.

Alcatraz

This isn't quite true; they both are accessible from the codebehind, but interestingly enough only the x:Name can be updated at runtime. Nutty. – Susette

Answer 9

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.

Drusi

If there's no difference, then why would there be two ways of doing the same thing? Both ways existed in the first release of WPF. – Girardo

Answer 10

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

Bedrabble

Tempted to -1 x: refers to a different XML namespace, true, but that's not actually a useful answer to the Q which is about when do you need ot use one no the other. :/ – Mayo

Answer 11

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.

Read More on MSDN...

Teocalli

Answer 12

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).

Inductive

Answer 13

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.

Bergmans

Answer 14

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

Minster

This is incorrect, both Name and x:Name are not scoped by the XAML nesting. They are both accessible for binding anywhere in XAML. Maybe you made a typo? – Wrier

Answer 15

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.

Mcdonald