Is there any way to fast override the "value" name for a new variable that is placed in the set block in C#?
class Foo {
string name = "guy";
public string Name {
get {
return name;
}
set {
if (value != "foo") {
name = value;
} else {
Console.WriteLine("sorry I already took that one!");
}
}
}
For example in swift I could write it this way:
var Name: String {
get {
return name;
}
set (newName) {
if (newName == "Foo") {
print("sorry I already took that one!")
} else {
name = newName;
}
}
}
I know I can easily solve it by assignment at the beginning of the block but the approach with naming the value in parenthesis just after the keyword is very clear to me so just wanted to ask is there another solution.
Basically, no. It is a language feature that value is the contextual keyword that always represents the incoming value in a set accessor (and in custom event accessors).
You can fake it:
var newName = value;
but... you get better syntax highlighting with value than newName, and any C# reader automatically knows what value represents in that context.
Related
I want to store and retrieve my configs from database. I have written two methods setConfig(“configName”, value) and getConfig(“configName”) and I use them in my properties:
public long MyConfig1
{
get
{
return getConfig("MyConfig1");
}
set
{
setConfig("MyConfig1", value);
}
}
But I have to write the string of the name for all of properties.
Is it possible to get name or any reference to the current property in set and get in C#?
Something like this:
public long MyConfig1
{
get
{
return getConfig(getName(this));
}
set
{
setConfig(getName(this), value);
}
}
If you have access to the getConfig and setConfig methods, modify those methods as shown below. This is the most clean solution.
// using System.Runtime.CompilerServices;
public long MyConfig1
{
get
{
return getConfig();
}
}
private long getConfig([CallerMemberName] string propertyName = null)
{
}
However if you do not have access to modify those methods, use nameof in each setter and getter.
public long MyConfig1
{
get { return getConfig(nameof(MyConfig1)); }
}
You can write a method to use the caller-information attributes:
// Put this anywhere
public static string GetCallerName([CallerMemberName] name = null)
=> name;
Importantly, when you call this, don't supply an argument: let the compiler do it instead:
public long MyConfig1
{
get => GetConfig(Helpers.GetCallerName());
set => SetConfig(Helpers.GetCallerName(), value);
}
Or you could use the same attribute in the GetConfig and SetConfig methods, of course, and then just not supply an argument when you call them.
I'm attempting to re-write a VB.NET WebForms application in C# MVC. I'm having an issue with one of the properties when using Entity Framework to instantiate a class.
I have a column in my database "VATInclusive", which is of type 'int'. The original application implicitly converted a "1" or "0" to "true" or "false", but when trying to do this in my application, I get the following error:
The 'VATInclusive' property on 'Shop' could not be set to a
'System.Int32' value. You must set this property to a non-null value
of type 'System.Boolean'.
I can't simply change the type in the database as other applications make use of the table. I've tried using the following code to convert the value, but it seems to only return false, regardless of whether the database has a "0" or a "1"... Can anybody suggest a solution to this?
[Column("VATInclusive")]
private int _VATInclusive { get; set; }
[NotMapped]
public bool VATInclusive
{
get
{
if (_VATInclusive == 0)
{
return false;
}
else
{
return true;
}
}
set
{
if(_VATInclusive == 0)
{
this.VATInclusive = false;
}
else
{
this.VATInclusive = true;
}
}
}
Following some advice from the answers provided, I have rectified the issue. The issue lay with the setter accessor and also with the _VATIncusive property. By changing the code to the following I have managed to get the system to work as I expected.
However, I feel that this isn't the best approach, but it appears to be working correctly...
EDIT : EDIT : I've reduced the get accessor as per advice from Ryan and hvd..
EDIT : I'm not sure of the implications of having both properties set to public. But I don't think this is going to be an issue.
[Column("VATInclusive")]
public int _VATInclusive { get; set; }
[NotMapped]
public bool VATInclusive
{
get
{
return _VATInclusive != 0;
}
set
{
_VATInclusive = value ? 1 : 0;
}
}
If you store the column as a bit, Entity Framework automatically queries it as a Boolean for you.
You can't have a setter accessor assign to itself - this will always result in a StackOverflowException. In the below code:
set
{
if(_VATInclusive == 0)
{
this.VATInclusive = false;
}
else
{
this.VATInclusive = true;
}
}
every time this.VATInclusive is assigned to, the control flow returns to the beginning of the set accessor. This obviously can never complete.
You have some typos on your setter. I think you mean for it to be:
set
{
if(value == false)
{
_VATInclusive = 0;
}
else
{
_VATInclusive = 1;
}
}
Basically, "value" represents the bool value passed in to your setter (to be converted in to an integer). _VATInclusive is the actual object that you want to be modifying under-the-hood.
In your set, you need to compare against value:
if (value == 0)
I have a class that looks the following way:
public class StackOverflowQuestion {
private string _question;
public string Question {
get { return _question; }
set { _question = value; }
}
public StackOverflowQuestion(string question) {
_question = question;
}
public override string ToString() {
return _question;
}
}
Now, the value "question" isn't allowed to be null or empty and the user should be notified via a ArgumentNullException - but where should it been thrown? According to the 'fail-fast' principle -> Everywhere.
public class StackOverflowQuestion {
private string _question;
public string Question {
get { return _question; }
set {
if(!String.IsNullOrEmpty(value))
_question = value
else throw new ArgumentNullException("value");
}
}
public StackOverflowQuestion(string question) {
if(!String.IsNullOrEmpty(question))
_question = question;
else throw new ArgumentNullException("question");
}
public override string ToString() {
if(!String.IsNullOrEmpty(_question)) return _question;
else throw new ArgumentNullException("_question");
}
}
Now this is obviously ridiculous and extremely repetitive. But it seems right: If the value is set through .ctor, it fails directly after a short check. When its set through the property, it fails directly after a short check.. but who expects exceptions on a setter? And when I output the string, I expect a string, not an exception for something that should have happend long ago, but again: If it's wrong, it should fail ASAP, even if 'soon' is quite late.
So, where should the only exception handling been done? Am I asking for a 'best-practice', or is this a taste thing?
Since _question is private, there's no need to check whether it is null in ToString() (unless you're just sanity checking your own code).
You can avoid the check in the constructor by having the constructor use the property setter. Thus, I'd recommend:
public class StackOverflowQuestion {
private string _question;
public string Question {
get { return _question; }
set {
if(string.IsNullOrEmpty(value))
// to make this more transparent when thrown through the constructor, it might
// be preferable to throw a real error message like "Question: cannot be null or empty"
throw new ArgumentException("value");
this._question = value;
}
}
public StackOverflowQuestion(string question) {
this.Question = question;
}
public override string ToString() {
return this.Question;
}
}
A few things to note:
1. You should throw ArgumentException rather than ArgumentNullException for empty strings (if you want you can do 2 checks and still throw ArgumentNullException for nulls).
2. While the approach uses less code, the one disadvantage is that the error message users get is slightly worse than when they pass null to the constructor, since the failure happens 2 levels deep instead of one.
You only need to test it once - in the single place where you set the variable, having changed the constructor to use the property:
public class StackOverflowQuestion
{
private string _question;
public string Question
{
get { return _question; }
set
{
if (String.IsNullOrEmpty(value))
{
throw new ArgumentException("Question cannot be null or empty",
"value");
}
_question = value;
}
}
public StackOverflowQuestion(string question)
{
Question = question;
}
public override string ToString()
{
return Question;
}
}
The one downside here is that the "bad parameter" name will be value rather than question when it's null in the constructor, but I think that's a price worth paying. An alternative is just to use the message, and not specify the parameter name.
You may want to separate out null from empty, so that you can throw an ArgumentNullException when it's null - but you shouldn't be throwing ArgumentNullException when it's just empty.
You don't need to perform any checks when fetching the value, as you know it will never be null or empty, because you're preventing it from ever being set that way.
You should also consider whether you could make the class immutable, at which point you'd only need to test in the constructor as there wouldn't be a setter...
I would rather make it immutable:
public class StackOverflowQuestion
{
public string Question
{
get; private set;
}
public StackOverflowQuestion(string question)
{
if (String.IsNullOrEmpty(question))
throw new ArgumentNullException("question");
Question = question;
}
public override string ToString()
{
return Question;
}
}
I want to assign some default value to a property or want to replace some character like given below. Is it a correct syntax or should i do this by creating a variable.
public string Login_Name
{
get
{ return this.Login_Name; }
set { this.Login_Name = value.Replace("'", "''"); }
}
By accessing Login_Name the get will return Login_Name again leaving you with an infinite loop (StackOverflowException).
You should use properties to get and set private members:
public string Login_Name
{
get
{
return _login_Name;
}
set
{
_login_Name = value;
if (!string.IsNullOrEmpty(_login_Name))
{
_login_Name = _login_Name.Replace("'", "''");
}
}
}
private string _login_Name;
If you meant to use an auto-implemented property, it would look like this:
public string Login_Name {get;set;}
But auto-implemented properties cannot have any additional logic applied to their gets or sets.
That won't work; you'd effectively be creating an infinite loop.
Use a separate private field instead:
private string m_loginName;
public string Login_Name
{
get
{
return m_loginName;
}
set
{
m_loginName = !string.IsNullOrEmpty(value) ? value.Replace("'", "''") : value;
}
}
What you have written is not an auto-implemented property. An auto-implemented property would look like this:
public string Login_Name { get; set; }
Here is a quote from MSDN, emphasis mine:
In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors.
When you have extra logic like in your example you cannot use an auto-implemented property. You can use an ordinary property and declare the backing field yourself.
private string loginName;
public string LoginName
{
get
{
return loginName;
}
set
{
loginName = (value == null) ? null : value.Replace("'", "''");
}
}
I do it like this.
private string _Login_Name = "Some Default";
public string Login_Name
{
get { return _Login_Name; }
set
{
_Login_Name = value.Replace("'", "''"); //might want to check for null first
}
}
You'll have to set a variable, otherwise you'll end up with infinite recursion and a Stack Overflow. With what you have, your setter is calling itself with:
this.Login_Name = ...
This is in the same way that your getter is calling itself with:
return this.Login_Name;
It's correct. The only problem in the snippet that you provided is the recursive call of setter method of the property.
set { this.Login_Name = value.Replace("'", "''"); }
you should set value to some private field rather than recursively to the property itself, for example:
set { loginName = value.Replace("'", "''"); }
This question already has answers here:
What is the { get; set; } syntax in C#?
(20 answers)
Closed 8 years ago.
I see this quiet often in C# documentation. But what does it do?
public class Car
{
public Name { get; set; }
}
It is shorthand for:
private string _name;
public string Name
{
get { return _name; }
set { _name = value; }
}
The compiler generates the member variable. This is called an automatic property.
In simple terms they are referred as property accessors. Their implementation can be explained as below
1.get{ return name}
The code block in the get accessor is executed when the property is Read.
2.set{name = value}
The code block in the set accessor is executed when the property is Assigned a new value.
Eg.(Assuming you are using C#)
class Person
{
private string name; // the name field
public string Name // the Name property
{
get
{
return name;
}
set
{
name = value;
}
}
}
Now when you refer to this property as below
Person p = new Person();// Instantiating the class or creating object
'p' of class 'Person'
System.Console.Write(p.Name); //The get accessor is invoked here
The get accessor is invoked to Read the value of property i.e the compiler tries to read the value of string 'name'.
2.When you Assign a value(using an argument) to the 'Name' property as below
Person p = new Person();
p.Name = "Stack" // the set accessor is invoked here
Console.Writeline(p.Name) //invokes the get accessor
Console.ReadKey(); //Holds the output until a key is pressed
The set accessor Assigns the value 'Stack" to the 'Name property i.e 'Stack' is stored in the string 'name'.
Ouput:
Stack
It's an automatic read-write property. It's a C# 3.0 addition. Something like:
public class Car {
private string name;
public string Name { get { return name; } set { name = value; } }
}
except that you can't directly access the backing field.
It's called an Auto-Implemented Property and is new to C# 3.0. It's a cleaner syntax when your access to the property doesn't need any special behavior or validation. It's similar in function to:
public class Car
{
private string _name;
public string Name
{
get { return _name; }
set {_name = value; }
}
}
So it saves a fair amount of code, but leaves you the option later to modify the accessor logic if behavior or rules need to change.
It is the equivilent of doing:
private string _Text;
public string Text
{
get { return _Text; }
set { _Text = value; }
}
Except you don't have access to the private variable while inside the class.
Auto-Implemented Properties
SUMMARY:In C# 3.0 and later, auto-implemented properties make
property-declaration more concise when
no additional logic is required in the
property accessors.