I am creating a class which contains options/configuration values for my application. I would like to bind some sort of get and set event to all the options in my options class. My class looks something like this:
public class Options
{
public int Option1 { get; set; }
public bool Option2 { get; set; }
public string Option3 { get; set; }
// etc.
}
I do not want to implement getters and setters for all these properties which will all look identical. Ideally what I want is for these properties to all behave as if they were defined something like this:
private int _option1;
public int Option1
{
get => option1;
set
{
_option1 = value;
OnOptionChanged("Option1", value);
}
}
I know the above is possible and will work but it's not very convenient. Some thoughts I've had are for my Options class to extend DynamicObject and override TrySetMember, but this is only called when a member does not exist in the class. I need my option properties to be defined as I need to add XML documentation to each of them.
So, finally, is there any way to implement the above without adding an event call to each of my properties' setters?
Alternatively, is there a way to document (automatically, and then export to the usual XML documentation file) properties which are not strictly present in a class?
You can't do that without an IL-weaving tool like PostSharp, however: you can get closer; consider:
private void OnOptionChanged<T>(ref T field, T value,
[CallerMemberName] string name= null)
{
field = value;
OnOptionChanged(name, value);
}
...
public int Option1 {
get => _option1;
set => OnOptionChanged(ref option1, value);
}
which is at least slightly less to repeat.
Related
Below, when I attempt to use the _currentTemp variable, that was supposed to be auto-generated via the auto properties functionality, I get a variable not found message:
The name _currentTemp does not exist in the current context.
Using { get; set; } should automatically create this private variable (_currentTemp), right?
public class DogTemperature
{
public double CurrentTemp { get; set; }
public DogTemperature(double dCurrentTemp)
{
_currentTemp = dCurrentTemp; //***this line***
}
}
Backing fields created by auto-properties are not available for you to interact with in your source code, as it is generated by the compiler.
If you want to interact with the backing field, you'll need to create your properties the verbose way.
In my opinion defining a property like this is complely pointless if all you want to do is store a value.
double _currentTemp;
public double CurrentTemp
{
get { return _currentTemp; }
set { _currentTemp = value; }
}
All you're doing here is giving the private context two ways to set the same value. You can set the _currentTemp field directly or you can set the CurrentTemp property which sets the _currentTemp field. If you are not doing anything with the property then just use the default get/set like this:
public double CurrentTemp { get; set; }
If you need to do more complex work in the property then go ahead and define a field like this. More complex work such as conditions, calculations or raising events:
double _currentTempFarenheit;
double _currentTempCelcius;
public double CurrentTemp
{
get
{
if(UseFarenheit)
return _currentTempFarenheit;
else
return _currentTempCelcius;
}
set
{
if(UseFarenheit)
_currentTempFarenheit = value;
else
currentTempCelcius = value;
}
}
Furthermore if you only want the value of your property to be set by the constructor of your DogTemperature class then you should make the setter private. This will only allow the property to be publically read.
public double CurrentTemp { get; private set; }
Based on #Alex Gravely's answer...
If I'm understanding your necessity for a full property: you can create full properties and backing fields like this:
private double _currentTemp;
public double CurrentTemp
{
get { return _currentTemp; }
set { _currentTemp = value; }
}
Then in your constructor for DogTemperature, you just need to set the CurrentTemp to the double you passed in:
public void DogTemperature(double temp)
{
DogTemperature = temp;
}
Depending on what usage you want to get out of the CurrentTemp property - i.e. to display in a View and updating it; you may want to read into implementing INotifyPropertyChanged. Here's a link: https://msdn.microsoft.com/en-us/library/ms229614(v=vs.100).aspx
If it is just a plain old property, and not used for anything special (such as in a model, for example); then the
public double DogTemperature { get; set; }
property will suffice; setting it in the constructor as above.
Hope this helps!
Usually I would build my field like this:
private string name;
public void setName(string name){
this.name = name;
}
public string getName(){
return name
}
that works perfectly when doing this: string myString = object.getName() or object.setName("Alex").
However, I thought I might give the inbuilt C# functions a try.
So I did this:
private string name { get; set; }
however, that won't work at all. When I try to access the field with object.name, I can't even access it due to private restriction.
Did I misunderstand something about these predefined get/sets?
If I had to mark every field as public, why should I even use getters or setters? I could access the field like in the snippet above without get and set?
You're mixing up way too many things - you might want to read a book on C#, really. It usually takes some time to get rid of some of the preconceptions from your old programming language - but you really do want to do that; even Java and C# are incredibly different when you go beyond the surface appearance.
First, nothing is forcing you to use auto-properties. If you want to use properties while keeping your manual backing fields, you can simply use this:
private string name;
public string Name { get { return name; } set { name = value; } }
If you do want to use auto-properties, you have to understand that the backing field is hidden - you're only declaring the property; and you want that property to be public (though you can also use accessibility modifiers on the individual get/set "methods", e.g. private set). But the field is never accessible - it's "always" behind the property.
To mirror your original code, this is what you want:
public string Name { get; set; }
Only if you ever need to move away from using auto-properties (that is, you need to add some logic to either the getter or the setter), you will have to reintroduce the manual backing field, and stop using auto-properties - see the first code sample in my answer.
Did I misunderstand something about these predefined get/sets?
Yes, you did. The property itself has to be public. If you're using auto-properties, then you can't do any validation since the backing field is compiler generated. If you want to actually do something with the value before, you can use a property with a backing field:
private string name;
public string Name
{
get { return name; }
set
{
if (string.IsNullOrEmpty(name))
throw new ArgumentException("name cannot be null");
name = value
}
}
Because this:
public string Name { get; set; }
Generated a backing field like this:
[DebuggerBrowsable(DebuggerBrowsableState.Never), CompilerGenerated]
private string <Name>k__BackingField;
public string Name
{
[CompilerGenerated]
get
{
return this.<Name>k__BackingField;
}
[CompilerGenerated]
set
{
this.<Name>k__BackingField = value;
}
}
Just do
public string Name { get; set; }
That compiles down to a private field with an unspeakable name, and a public property. That public property has a public get method and a public set method.
Seems to be exactly what you want.
Alternatively, use
public string Name { get; private set; }
Your get method will be public as before, but the set method will be private then.
As of C# 6 (Visual Studio 2015), you can even do
public string Name { get; }
In that case, there is no set method, not even a private one, but you can assign to the underlying field through the property in the constructor.
Did I misunderstand something about these predefined get/sets?
Yes, a bit.
If I had to mark every field as public, why should I even use getters or setters? I could access the field like in the snippet above without get and set?
This is the part that you're missing. The syntax you are talking about it called an auto-implemented property. That is, when you write:
public string Name { get; set; }
the C# compiler generates a private field, getter, and setter behind the scenes for you. You can see them if you look at the metadata for your class, and get access to them via reflection. They have the exact same names as the getter or setter you would write yourself (typically get_Name and set_Name). The only difference is, you didn't have to write them.
The reason to do this is because most getter/setter pairs only exist to add a layer of abstraction over a private field, and consist of a single return name or name = value line of code. If that's all you want, you may as well let the compiler write it for you.
However, if you ever needed something more complex, you can manually implement the getter and setter yourself, and callers won't know the difference. In other words, if you change:
public string Name { get; set; }
to
private string name;
public string Name
{
get
{
return name;
}
set
{
name = value;
RecalculateSomeStuff();
}
}
then the metadata for your class is identical. Anyone using your class does not have to even be recompiled to pick up the new setter, because as far as the callers are concerned, they're still called set_Name directly.
What the others want to tell you is that you should deferentiate between fields (privates) and properties (public) (is not a rule but a convention)
private string name;
public string Name{ get; set;}
// you can acces to the property:
var objectName = YourObject.Name
// and set the value of your property:
YourObject.Name = "whatever"
First of all the equivalent of your code is
private string _name;
public string Name
{
get {return _name;}
set { _name = value; }
}
OR simply
public string Name { get; set; }
To define the accessibility level of the "Name" field, you put the access modifiers (public, protected, etc.) before get or set
Example
//Read only properties
public string Name
{
get {return _name;}
private set { _name = value; }
}
To have more details and see difference between public fieal and public property see Difference between Auto - Implemented Properties and normal public member
PS :
To write this in Visual studio you can use snippet, type prop keyword then tab key or propfull and press tab key. press tab key our shift+tab to navigate between highlighted fields
I've just gotten started learning c#, and I'm struggling a bit with the getter and setter shorthand.
As I understand it, the two methods below are equivalent. Is this correct?
//Method 1
public string name { get; set; }
//Method 2
private string name
public string getName() { return name;}
public string setName(string newName) { this.name = newName; }
Secondly, how does this work if we wanted different access modifiers on the getter/setter and the instance variable. The following code errors, telling me that the accessor must be more restrictive than the property and that I can't specify modifiers for bother accessors. Can somebody please clarify?
private int maxTime { public get; public set; }
EDIT: To clarify, I have no specific goal, only to understand. I don't understand what this shorthand notation does. In other languages I've had private instance variables and used public getters and setters to manage these instance variables. It allows this if I write out the methods on my own, but not with this shorthand notation. Why is this?
EDIT2: One last question to check my understanding. Both of the code snippets below use properties to manage the maxTime variable. The only difference between the two is style. Is this correct?
private int maxTime;
public int MaxTime{ get; set; }
vs
private int maxTime;
public int MaxTime
{
get { return maxTime; }
set { maxTime= value; }
}
Instead of the wrong private int maxTime { public get; public set; },
you can write a property that will populate a private field:
private int maxTime;
public int MaxTime
{
get { return maxTime; }
set { maxTime = value; }
}
This is useful when you want to apply logic when getting or setting the value of maxTime. if not, a simple shorthand property will do:
public int MaxTime { get; set; }
You can create a property that have a public getter but a private setter, like this:
public int MaxTime { get; private set; }
This is useful for readonly properties, and usually the property is populated in the constructor of the class.
You can even create a property where the setter is public but the getter is private, though I can't imagine any scenario this would be useful. Moreover, code standards claim that such a thing should be a method, not a property.
(read this)
public int MaxTime { private get; set; }
The answer your question in edit 2 is no.
the first code never change the private int maxTime, while the second one does. However, if inside your class you only use the property MaxTime, then they are functionally equivalent.
Update:
Since c# 6 you can write shorthand properties without a setter:
public int MaxTime {get;}
These properties can only be initialized in the constructor, or hard coded like this: (also a new feature of c# 6)
public int MaxTime {get;} = DateTime.Now;
This is useful for immutable properties (unlike readonly properties, the value of such a property can not change even inside the hosting class once initialized.
//Method 1
public string name { get; set; }
//Method 2
public string name
public string getName() { return name;}
public string setName(string newName) { this.name = newName; }
The above 2 methods are not equivalent.
It would be more accurate to compare them like this:
//Method 1
public string name { get; set; }
//Method 2
private string name; // this is private, not public.
public string Name // this is a property, not a method.
{
get
{
return this.name;
}
set
{
this.name = value;
}
}
And if you want to play with access modifiers, like make the get public, and the set private, then you would do it like this:
public int maxTime { get; private set; }
More info on Auto-Implemented Properties and the compiler magic that goes on behind the scenes.
public string name { get; set; }
What you have is Auto-Implemented property, which would internally have a backing private field (and compile time methods for get/set).
In C# code this would be equivalent to:
private string _name;
public string name
{
get { return _name; }
set { _name = value; }
}
At compile time, get/set are converted into method calls, somewhat similar to what you have.
For:
private int maxTime { public get; public set; }
The error is pretty clear, you can't have less restrictive access specifiers than the property itself. For example, if you want your public property to have a public get, but if you only want to allow setting the property from inside the class you can do:
public int maxTime { get; private set; }
You should also see: .Net Naming conventions, It would be better if you follow that, so you could have your property name starting with an upper case letter.
The first method is simply C# syntactic sugar for an automatically implemented property. It provides an implementation of the appropriate accessors when you come to compile it.
The second example is different. Here, you have a public-scope field (normally a no-no because of the principle of encapsulation) and two methods which access the variable. There's a subtle difference in semantic usage; typically properties are used to expose state, whereas a method normally indicates that the method has some computation behind it and isn't just going to return or change current state (again, this is a convention, not a hard-and-fast rule) Methods are normally styled with VerbAction naming (public Thing GetAThing() { }).
Auto-generated properties can have different access modifiers, but must only make the get or set less accessible than the overall modifier.
public int X { get; private set; } // OK
public int X { private get; set; } // OK
private int X { public get; public set; } // NOT OK
When you use a property like in Method 1 (public string name { get; set; }), the compiler automatically generates a private backing string variable and public getter and setter methods.
The general idea is to make fields private and allow access only through public getter/setter methods. So if you use Method 2 declare the variable private.
I'd recommend to use ILDASM to peruse the generated IL, it helps to see what's going on under the hood.
The second error is simply what the compiler says. The visibility of the constructs must be consistent
New to C#, and I understand that encapsulation is just a way of "protecting data". But I am still unclear. I thought that the point of get and set accessors were to add tests within those methods to check to see if parameters meet certain criteria, before allowing an external function to get and set anything, like this:
private string myName;
public string MyName;// this is a property, speical to c#, which sets the backing field.
private string myName = "mary";// the backing field.
public string MyName // this is a property, which sets/gets the backing field.
{
get
{
return myName;
}
set
{
if (value != "Silly Woman"){
myName = value;
}
}
}
But I've been seeing code in c# which just looks like this:
public string MyName { get; set; }
Why would you just have a get and set with nothing in there, - isn't that the same as just declaring your private backing field public? If you can just get and set it from outside, why wouldn't you just do it directly?
Indeed, creating an auto-property as follows:
public string Name { get; set; }
is identical to building a property backed by a field:
private string _name;
public string Name {
get { return _name; }
set { _name = value; }
}
The point of these properties is not to hide data. As you observed, they don't do this. Instead, these properties can do other stuff instead of just working with a field:
public string Name {
get { return _name; }
set { if (value == null) throw new Exception("GTFO!"); _name = value; }
}
Another thing is, you can make properties virtual:
public virtual string Name { get; set; }
which, if overridden, can provide different results and behaviours in a derived class.
By using public string MyName { get; set; }, you leave an ability to change its logic later without the need to recompile/change other code that uses your property.
For example, if you are making a library and v1 uses a field and v2 uses a property, applications that work with v1 will not work with v2 without recompilation (and, potentially, code changes if they are written in some .NET language that has different syntax for accessing fields).
Another important difference is in serialization scenarios -- a lot of them do not support fields. Also any interface that requires a property can not be implemented without using one, but depending on interface it may not be required to do any additional checks/logic in it.
It makes it easier to add logic later. If you have a class that has a public field that you want to change to a property, you have to recompile everything that uses your class. That's a key point that I didn't understand initially.
If you have a class:
public class MyClass
{
public string MyString;
}
You could access the value like this:
var myClass = new MyClass();
string s = myClass.MyString;
Now change that to a property:
public class MyClass
{
public string MyString { get; set; }
}
How is it accessed? The exact same way:
var myClass = new MyClass();
string s = myClass.MyString;
So no big deal, right? Well, actually....
Properties are actually compiled into getter and setter methods:
get_MyString() and set_MyString(string value)
So the two methods do produce different compiled code. Now if all your code that uses this class is in the same project, is not as big a deal, because it will all be compiled together. But if you have an API library that you've distributed, it can be a much bigger deal to update.
Because it is easier to change the Code if you want to add the checks/tests later on.
Especially if you have many inheritance and many classes in your code it is very hard to change the implementation from a public variable to a public Property.
Moreover you can add to the get and set within the property different attributes, e.g. if you are using reflection. The get and set of the property are internally different methods. If you have just a public variable /field it is not possible to added different properties to the different access ways.
Yeah, but you can easily change it to:
public string MyName { get; private set; }
Plus, properties are used in other scenarios, like DataContracts and Serialization... so, this is a nice feature... (Mostly, syntactic sugar. I think) EDIT: I take that back.. you can apply virtual to it, so it's not the same
In C# do properties need to reference private member variables, or can I just declare the properties and use them directly in the class code?
If the former is the best practice, then does that rule out using C# property short-hand? I.e.
public string FirstName { get; set; }
Properties, when implemented like this:
public string FirstName { get; set; }
Automatically create a private member variable (the compiler does this for you), so you don't have to worry about it. This will behave exactly the same as if you do:
private string firstName;
public string FirstName {
get { return firstName; }
set { firstName = value; }
}
There is no reason not to use the automatic properties ( { get; set; } ). The provide the same advantages as making your own private member variable.
In addition, if you later decide you need to do extra processing (for example, if you decide to implement INotifyPropertyChanged in your property setter), you can add this without changing your public API, but putting a backing field in manually.
You don't need properties to access private fields but in general it is considered best practice.
And you can use auto-properties (short hand) untill you need to add more functionality to a property, like validation. Changing it to a 'real' property is always a non-breaking change.
Properties created like this
public String Caption{ get; set; }
this will be compiled as
[CompilerGenerated]
private string <Caption>k__BackingField;
public string Caption
{
[CompilerGenerated]
get
{
return this.<Caption>k__BackingField;
}
[CompilerGenerated]
set
{
this.<Caption>k__BackingField = value;
}
}
The above code is extracted after compilation using reflector tool.
They do not need to reference private member variables. You can use them directly in the class.
Properties do not need to reference private member variables. It is best practice, though, to have them do so. You can think of properties as methods if it makes it easier to understand. You can run code inside of them. You can return whatever you want. You can call methods and use private member variables. You can even simply return a constant.
I use private member variables in almost all cases. It allows me to create a readonly property, or to provide some rules to those outside my class of getting or setting properties that my class doesn't have to follow.
To add on to Reed's answer, inside of your code (within the class itself) the member functions should adhere to this and actually use the Property rather then the actual private member. For instance if you had this:
public string FirstName { get; set; }
And you had a strange method called public char GetFirstLetter() that returned the first letter in a person's first name you'd want to do it like this:
public char GetFirstLetter()
{
return FirstName[0];
}
Instead of actually using your private variable. When you set a property a programmer may have written code to set it in a particular manner. So it only makes sense to simply use that property within your class methods.
C# can reference private variables as in:
public class A
{
private string _b;
public string B
{
get { return _b; }
set { _b = value; }
}
}
The get;set; designation is automatic properties which when compiled will generate the private variable for you, as a way to make it easy to setup your code.
Using properties is the best way to provide a method of control and security to the attributes in a class, always keep the attributes private if possible.
if you use like
public string FirstName { get; set; }
compiler will automatically adds getters and setters for this property automatically.it not a bad practice.
Here is the proof
if you declare
private string firstName;
public string FirstName
{
get { return firstName; }
set { firstName = value; }
}
like this also compiler will takes it as
so its not ruled out... :)