You know how you can have a property that automatically generates a backing field? Like if I go:
public String SomeProperty {get; set;}
I know that if I want to add code to that property I have to create the backing field as so:
public string someProperty = string.Empty;
public string SomeProperty
{
get { return someProperty; }
set
{
someProperty = value;
DoSomething();
}
}
Basically, what I want to know is... is there any way to do this but without having to create the backing field? For example I could use it to trigger some kind of event that occurs when a property is set. I'm looking for something like this:
public string SomeProperty
{
get;
set { this.OnSomeEvent; }
}
But I know that'll cause a compile error because get needs do declare a body if set does.
I've researched and I cant find anything, but I thought I'd check to see if anyone knew.
I guess what I'm really after is some way to trigger an event when a property is changed but without having to add all that extra clutter. Any suggestions?
Simple answer is no, you can't have it both ways. From .NET Docs:
In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors.
There are not any solutions for this built into the framework, and you cannot modify existing types via reflection (in order to add the logic at runtime). The only way to accomplish this seems to be at compile time.
There is a product http://www.postsharp.net/ that can accomplish this (intercept property/method calls), and there does appear to be a free edition.
The field keyword might be added to C#, see https://github.com/dotnet/csharplang/issues/140, which removes "when no additional logic" requirement for auto properties.
It didn't make it into C# 10 nor 11, but latest comment from compiler team says C# version 12 might have it. They release yearly, so that would be Nov 2023.
Related
I have to make many combination of field and property. I cannot use the implicit property version "{ get; set; }" since the fields need some attributes.
So, in Visual Studio Express 2013, is there a way to have a shortcut to create a property associated with a field I just ended up writing?
Let's say I write;
private MyType myData;
and I press CTRL+P (whatever the shortcut), and it adds
public MyType MyData
{
get { return myData; }
set { myData = value; }
}
just after.
Is it possible?
EDIT:
The Express version however does only have two refactoring functionalities: rename and extract method, the other functionalities like encapsulate are not present.
I guess I'm stuck.
By what you are asking 3 simple clicks will do it like this:
rigth-click in your field then Refactor-->EncapsulateField
And your done.
Check this out:
http://msdn.microsoft.com/en-us/library/z41h7fat.aspx
this might also be useful (Create your own snippets) :
http://msdn.microsoft.com/en-us/library/vstudio/ms165394.aspx
here you have all the code snippets you need including "prop", which is the one you need now!
Hope it helps
Type prop
then press tab
then enter the property name
then press ctrl+.
then click on convert to full property
You should use code snippet and assign hotkey for it.
More information about managing code snippets here: http://msdn.microsoft.com/en-us/library/ms165394.aspx
Is it possible to have an attribute placed on a property intercept an assignment call to that property?
An example of how I would use this is to make it so that a string property with this attribute on it would be set to string.Empty when the user assigns null.
I'm sure there are a lot of other possible uses for something like this, but at the moment this is what I'm looking for.
EDIT:
For example:
class A
{
[NotNullableString]
public string SomeString { get; set; }
}
And NotNullableStringAttribute would check the input value for the set and if it is null replace it with string.Empty instead.
If you want to do this using C# Attributes you will need to use IL weaving.
The most popular library is PostSharp : http://ayende.com/blog/3640/first-steps-with-post-sharp The express version is free : http://www.postsharp.net/aspects
If you insist that there be no post build step in your workflow AND you get to use attributes, then the answer is that it is currently not possible.
I am working with WPF and MVVM, and so have a lot of properties in my view models that are bound to stuff in the view. The majority of these properties look like this...
private DateTime _newRevisionDate = DateTime.Now;
public DateTime NewRevisionDate {
get {
return _newRevisionDate;
}
set {
if (_newRevisionDate != value) {
_newRevisionDate = value;
RaisePropertyChanged(ViewModelUtils.GetPropertyName(() => NewRevisionDate));
}
}
}
I'm using MvvmLight, which is where the RaisePropertyChanged() method comes from, and have used the ViewModelUtils.GetPropertyName() method to create a string from the property name, avoiding the need for magic strings.
Now, the problem is that if I add a few such properties to a view model, I end up with a large amount of almost identical code. This just cries out for some clever refactoring, so I can just use a single line of code to define each property.
However, I haven't been able to find any way to do this yet. What would be nice is to be able to do something like the standard C# automatic properties...
public DateTime NewRevisionDate { get; set; }
...but have it call RaisePropertyChanged() whenever the property is set to a new value.
Anyone any ideas? Thanks
This just cries out for some clever refactoring, so I can just use a single line of code to define each property.
Well you can make it a single line now. It's just a very long line :)
C# 5 makes this slightly easier with caller info attributes, so you don't need the GetPropertyName part - and that's the ugliest part of your current code.
The other thing you could do would be:
set
{
_newRevisionDate = PossiblyFireEvent(RaisePropertyChanged, _newRevisionDate, value);
}
where PossiblyFireEvent would take the property name as an optional parameter using the caller info attributes, RaisePropertyChanged as a delegate to execute if the two values were unequal, and always return value. Not sure it's worth it though.
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
C# 3.0 Auto-Properties - useful or not?
My boss and I regularly argue about the benefits and disadvantages of using automatic properties.
public string Name { get; set; }
vs
private string name;
public string Name
{
get { return this.name; }
set { this.name = value; }
}
For
I am strongly in favor of using them because I have to write less code, I find it easier to understand the class when all the fields are coded that way and just saves me a lot of time in the long run (mostly because I write a bit less code each time).
Against
He argues that they break some programming principle because the fields should reflect the state of the object and by using a property instead of a field with a property to access it, I lose that information while debugging. (Boss if you read this and it's not exactly what you mean, feel free to comment ;))
What's everyone's take on this matter?
NOTE: I have looked at the duplicate and it doesn't talk about the against points which is the point of this question. It's just people saying "I love them"/"I don't care".
How do you give up that information? The property reflects the state of the object instead of the field - is it that big a difference?
The only time I want to have it backed by a field is if I need to do additional logic when setting it (ie: validation) or when I want to enforce a design pattern such as caching the value or singleton etc.
Perhaps my understanding of Auto implemented properties is flawed, but if the documentation is to be bekieved, it is still backed by a property. Auto-implemented properties are a shortcut for writing boilerplate code only. The complier expands the Auto property upon compiliation, right? If you look at the IL it should show you a backing field. I believe the backing field is the property name preceded with an underscore.
So, the field does reflect the state of the object AND you don't have to write as much code. The field is just hidden in the IDE, although you should still be able to access it using reflection, if you wanted to.
His argument is wrong (so perhaps you've mis-quoted it).
Anyway, it doesn't matter. You are exaggerating how much time you save. And with most real-world applications, you'll start off with an automatic property and eventually change it to be backed by a real field for various purposes. It's really a useless argument.
Between these two:
With Property:
class WithProperty
{
public string MyString {get; set;}
}
With Field:
class WithField
{
public string MyString;
}
Apparently I'm supposed to pick the first one. Why?
I've heard the argument that the point here is to allow interface changes, but
if I have the second one, and change it to the first one, no other code should
ever have to change. When recompiled everything's just going to point to the
property instead.
Am I missing something important here?
The most important difference is the fact, that if you use a field, and later need to change it to a property (say, to enforce some validation), then all libraries calling your code will need to be recompiled. It's true that you can compile the exact same code if the name stays the same - but the consumers of your code will still need to be recompiled. This is because the IL generated to get the value is different between a field and a property. If it already is a property, you can make a change without forcing consumers of your code to change.
This may or may not be an issue for you. But the property is almost the same amount of code, and is considered best practice. I would always go for the property.
The property can be changed later if you need to add validation or other logic without breaking other assemblies.
Also, the property can be used with databinding.
The important part you are missing is the gravity of this statement:
When recompiled
When your code point to a field and you change it to point to a property of the same name, the C# itself doesn't change, but the resulting IL does - it generates a method call to the getter or setter as appropriate.
Not every app has all of it's pieces contained in a single distributed unit. Many apps rely on interfaces for pluggability/expandability. If you have an app with an interface to a field and you want to change it to a property to take advantage of the power of properties, the app has to be recompiled and redistributed. You might as well just make it a property in the first place.
With a property, you can easily extend it to include new logic.
For example, if you need to add validation logic to the set.
This article goes into several additional reasons why you should prefer properties:
http://csharpindepth.com/Articles/Chapter8/PropertiesMatter.aspx