Related
I prefer this:
private string _indeks;
public string Indeks
{
get => _indeks;
set => _indeks = value;
}
Instead of:
public string Indeks { get; set; }
But I haven't found a way to enforce that code style in Resharper in "Code Cleanup"?
Does anyone know how to do that?
I'm going by this tutorial and trying to figure out how to have a DataMember without an auto property. Basically I have a field is a date time in epoch format and I want the property to be a DateTime so I'm trying to do the conversion in the property's get. I'm not sure how to format this exactly.
Since Code was requested please look at the following. :
// The date looks like this in the JSON
"someEpochDateTime": 1428785212000,
// I thought I could work around it using the following code, however
// I get a warning saying someEpochDateTime is never set.
[DataMember(Name = "someEpochDateTime")]
private long someEpochDateTime;
public DateTime test
{
get { return DateTimeConverter.FromUnixTime(someEpochDateTime); }
}
Using FromUnixTime
like this you can create datereturn property this will return date
[DataContract]
public class Mycontractclass
{
// Apply the DataMemberAttribute to the property.
[DataMember]
public DateTime datereturn
{
get
{
return this.dateCreated.HasValue
? this.dateCreated.Value
: DateTime.Now;
}
set { this.dateCreated = value; }
}
private DateTime? dateCreated = null;
}
Apparently my last edit actually works as a solution, I just get a compiler warning for some reason.
[DataMember(Name = "someEpochDateTime")]
private long someEpochDateTime;
public DateTime test
{
get { return DateTimeConverter.FromUnixTime(someEpochDateTime); }
}
I've read a bunch about auto implemented properties but I still don't quite get it. I have and entity:
public class News
{
public int NewsId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public DateTime Date { get; set; }
}
Now I don't want the user to set date himself every time a new entity of News type is created. I want the record to be saved automatically with the datetime it's created. Thinking about it I suggest that it's enough to just modify the set for my property to something like :
public DateTime Date
{
get;
set
{
Date = DateTime.Now;
}
}
But reading about the topic I saw that the standard way is to create private variable and use it instead in the implementation. That's where I get a little bit lost.
private DateTime _date = null;
public DateTime Date
{
Well I'm not sure for the getter and setter implementations. It seems reasonable to have something like : set { _date = DateTime.Now;} and I have no idea how to deal with the get part since I want this data to be fetched from the database so something like : get {return _date;} doesn't make much sense to me even though almost every example with auto implementedset` returns the private variable. But I think that if the property is an entity this is not making a lot of sense.
Some ways to return the current date:
public DateTime Date { get { return DateTime.Now; } }
or
public class News
{
public News()
{
Date = DateTime.Now;
}
public DateTime Date { get; private set; }
}
The first one will always return the current date/time, even if that instance was created some time ago. The second one will return the date/time the instance was created. Both prevent the user from setting that Date value.
You could add a constructor to your class and then initialize there your property.
public class News
{
// properties goes here
public News()
{
Date=DateTime.Now;
}
}
A far better constructor would be the following
public News(int newsId, string title, string content)
{
NewsId=newsId;
Title=title;
Content=content;
Date=DateTime.Now;
}
That way you could create an object of type News in a single line of code.
News news = new News(1,"title1","whatever");
Don't touch the getter and setter! They are auto generated from a template and will be overridden every once and a while. Instead, as you might have noticed the generated entities are declared partially, create a partial class and declare a constructor there that sets the _date or Date of you r entity to DateTime.Now on construction (just as you desired).
public partial class News
{
public News()
{
this.Date = DateTime.Now;
}
}
Does any one know how I can specify the Default value for a DateTime property using the System.ComponentModel DefaultValue Attribute?
for example I try this:
[DefaultValue(typeof(DateTime),DateTime.Now.ToString("yyyy-MM-dd"))]
public DateTime DateCreated { get; set; }
And it expects the value to be a constant expression.
This is in the context of using with ASP.NET Dynamic Data. I do not want to scaffold the DateCreated column but simply supply the DateTime.Now if it is not present. I am using the Entity Framework as my Data Layer
Cheers.
You cannot do this with an attribute because they are just meta information generated at compile time. Just add code to the constructor to initialize the date if required, create a trigger and handle missing values in the database, or implement the getter in a way that it returns DateTime.Now if the backing field is not initialized.
public DateTime DateCreated
{
get
{
return this.dateCreated.HasValue
? this.dateCreated.Value
: DateTime.Now;
}
set { this.dateCreated = value; }
}
private DateTime? dateCreated = null;
Add below to the DateTime property
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
I have tested this on EF core 2.1
Here you cannot use either Conventions or Data Annotations. You must use the Fluent API.
class MyContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Blog>()
.Property(b => b.Created)
.HasDefaultValueSql("getdate()");
}
}
Official doc
There's no reason I can come up with that it shouldn't be possible to do through an attribute. It might be in Microsoft's backlog. Who knows.
The best solution I have found is to use the defaultValueSql parameter in the code first migration.
CreateTable(
"dbo.SomeTable",
c => new
{
TheDateField = c.DateTime(defaultValueSql: "GETDATE()")
});
I don't like the often reference solution of setting it in the entity class constructor because if anything other than Entity Framework sticks a record in that table, the date field won't get a default value. And the idea of using a trigger to handle that case just seems wrong to me.
It is possible and quite simple:
for DateTime.MinValue
[System.ComponentModel.DefaultValue(typeof(DateTime), "")]
for any other value as last argument of DefaultValueAttribute specify string that represent desired DateTime value.
This value must be constant expression and is required to create object (DateTime) using TypeConverter.
Just found this looking for something different, but in the new C# version, you can use an even shorter version for that:
public DateTime DateCreated { get; set; } = DateTime.Now;
A simple solution if you are using the Entity Framework is the add a partical class and define a constructor for the entity as the framework does not define one. For example if you have an entity named Example you would put the following code in a seperate file.
namespace EntityExample
{
public partial class Example : EntityObject
{
public Example()
{
// Initialize certain default values here.
this._DateCreated = DateTime.Now;
}
}
}
I think the easiest solution is to set
Created DATETIME2 NOT NULL DEFAULT GETDATE()
in column declaration and in VS2010 EntityModel designer set corresponding column property StoreGeneratedPattern = Computed.
Creating a new attribute class is a good suggestion. In my case, I wanted to specify 'default(DateTime)' or 'DateTime.MinValue' so that the Newtonsoft.Json serializer would ignore DateTime members without real values.
[JsonProperty( DefaultValueHandling = DefaultValueHandling.Ignore )]
[DefaultDateTime]
public DateTime EndTime;
public class DefaultDateTimeAttribute : DefaultValueAttribute
{
public DefaultDateTimeAttribute()
: base( default( DateTime ) ) { }
public DefaultDateTimeAttribute( string dateTime )
: base( DateTime.Parse( dateTime ) ) { }
}
Without the DefaultValue attribute, the JSON serializer would output "1/1/0001 12:00:00 AM" even though the DefaultValueHandling.Ignore option was set.
Simply consider setting its value in the constructor of your entity class
public class Foo
{
public DateTime DateCreated { get; set; }
public Foo()
{
DateCreated = DateTime.Now;
}
}
using System.ComponentModel.DataAnnotations.Schema;
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public DateTime CreatedOn { get; private set; }
I needed a UTC Timestamp as a default value and so modified Daniel's solution like this:
[Column(TypeName = "datetime2")]
[XmlAttribute]
[DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:yyyy-MM-dd}")]
[Display(Name = "Date Modified")]
[DateRange(Min = "1900-01-01", Max = "2999-12-31")]
public DateTime DateModified {
get { return dateModified; }
set { dateModified = value; }
}
private DateTime dateModified = DateTime.Now.ToUniversalTime();
For DateRangeAttribute tutorial, see this awesome blog post
There is a way. Add these classes:
DefaultDateTimeValueAttribute.cs
using System;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using Custom.Extensions;
namespace Custom.DefaultValueAttributes
{
/// <summary>
/// This class's DefaultValue attribute allows the programmer to use DateTime.Now as a default value for a property.
/// Inspired from https://code.msdn.microsoft.com/A-flexible-Default-Value-11c2db19.
/// </summary>
[AttributeUsage(AttributeTargets.Property)]
public sealed class DefaultDateTimeValueAttribute : DefaultValueAttribute
{
public string DefaultValue { get; set; }
private object _value;
public override object Value
{
get
{
if (_value == null)
return _value = GetDefaultValue();
return _value;
}
}
/// <summary>
/// Initialized a new instance of this class using the desired DateTime value. A string is expected, because the value must be generated at runtime.
/// Example of value to pass: Now. This will return the current date and time as a default value.
/// Programmer tip: Even if the parameter is passed to the base class, it is not used at all. The property Value is overridden.
/// </summary>
/// <param name="defaultValue">Default value to render from an instance of <see cref="DateTime"/></param>
public DefaultDateTimeValueAttribute(string defaultValue) : base(defaultValue)
{
DefaultValue = defaultValue;
}
public static DateTime GetDefaultValue(Type objectType, string propertyName)
{
var property = objectType.GetProperty(propertyName);
var attribute = property.GetCustomAttributes(typeof(DefaultDateTimeValueAttribute), false)
?.Cast<DefaultDateTimeValueAttribute>()
?.FirstOrDefault();
return attribute.GetDefaultValue();
}
private DateTime GetDefaultValue()
{
// Resolve a named property of DateTime, like "Now"
if (this.IsProperty)
{
return GetPropertyValue();
}
// Resolve a named extension method of DateTime, like "LastOfMonth"
if (this.IsExtensionMethod)
{
return GetExtensionMethodValue();
}
// Parse a relative date
if (this.IsRelativeValue)
{
return GetRelativeValue();
}
// Parse an absolute date
return GetAbsoluteValue();
}
private bool IsProperty
=> typeof(DateTime).GetProperties()
.Select(p => p.Name).Contains(this.DefaultValue);
private bool IsExtensionMethod
=> typeof(DefaultDateTimeValueAttribute).Assembly
.GetType(typeof(DefaultDateTimeExtensions).FullName)
.GetMethods()
.Where(m => m.IsDefined(typeof(ExtensionAttribute), false))
.Select(p => p.Name).Contains(this.DefaultValue);
private bool IsRelativeValue
=> this.DefaultValue.Contains(":");
private DateTime GetPropertyValue()
{
var instance = Activator.CreateInstance<DateTime>();
var value = (DateTime)instance.GetType()
.GetProperty(this.DefaultValue)
.GetValue(instance);
return value;
}
private DateTime GetExtensionMethodValue()
{
var instance = Activator.CreateInstance<DateTime>();
var value = (DateTime)typeof(DefaultDateTimeValueAttribute).Assembly
.GetType(typeof(DefaultDateTimeExtensions).FullName)
.GetMethod(this.DefaultValue)
.Invoke(instance, new object[] { DateTime.Now });
return value;
}
private DateTime GetRelativeValue()
{
TimeSpan timeSpan;
if (!TimeSpan.TryParse(this.DefaultValue, out timeSpan))
{
return default(DateTime);
}
return DateTime.Now.Add(timeSpan);
}
private DateTime GetAbsoluteValue()
{
DateTime value;
if (!DateTime.TryParse(this.DefaultValue, out value))
{
return default(DateTime);
}
return value;
}
}
}
DefaultDateTimeExtensions.cs
using System;
namespace Custom.Extensions
{
/// <summary>
/// Inspired from https://code.msdn.microsoft.com/A-flexible-Default-Value-11c2db19. See usage for more information.
/// </summary>
public static class DefaultDateTimeExtensions
{
public static DateTime FirstOfYear(this DateTime dateTime)
=> new DateTime(dateTime.Year, 1, 1, dateTime.Hour, dateTime.Minute, dateTime.Second, dateTime.Millisecond);
public static DateTime LastOfYear(this DateTime dateTime)
=> new DateTime(dateTime.Year, 12, 31, dateTime.Hour, dateTime.Minute, dateTime.Second, dateTime.Millisecond);
public static DateTime FirstOfMonth(this DateTime dateTime)
=> new DateTime(dateTime.Year, dateTime.Month, 1, dateTime.Hour, dateTime.Minute, dateTime.Second, dateTime.Millisecond);
public static DateTime LastOfMonth(this DateTime dateTime)
=> new DateTime(dateTime.Year, dateTime.Month, DateTime.DaysInMonth(dateTime.Year, dateTime.Month), dateTime.Hour, dateTime.Minute, dateTime.Second, dateTime.Millisecond);
}
}
And use DefaultDateTimeValue as an attribute to your properties. Value to input to your validation attribute are things like "Now", which will be rendered at run time from a DateTime instance created with an Activator. The source code is inspired from this thread: https://code.msdn.microsoft.com/A-flexible-Default-Value-11c2db19. I changed it to make my class inherit with DefaultValueAttribute instead of a ValidationAttribute.
I faced the same issue, but the one which works for me best is below:
public DateTime CreatedOn { get; set; } = DateTime.Now;
In C# Version 6 it's possible to provide a default value
public DateTime fieldname { get; set; } = DateTime.Now;
Using EntityTypeConfiguration, I get it like this:
public class UserMap : IEntityTypeConfiguration<User>
{
public void Configure(EntityTypeBuilder<User> builder)
{
//throw new NotImplementedException();
builder.Property(u => u.Id).ValueGeneratedOnAdd();
builder.Property(u => u.Name).IsRequired().HasMaxLength(100);
builder.HasIndex(u => u.Email).IsUnique();
builder.Property(u => u.Status).IsRequired();
builder.Property(u => u.Password).IsRequired();
builder.Property(u => u.Registration).HasDefaultValueSql("getdate()");
builder.HasMany(u => u.DrawUser).WithOne(u => u.User);
builder.ToTable("User");
}
}
Using the Fluent API, in OnModelCreating function in your Context class add following.
builder.Property(u => u.CreatedAt).ValueGeneratedOnAdd();
builder.Property(u => u.UpdatedAt).ValueGeneratedOnAddOrUpdate();
Note I'm using a separate type configuration class. If you did right in the function would be like:
builder.Enitity<User>().Property(u => u.CreatedAt).ValueGeneratedOnAdd();
public DateTime DateCreated
{
get
{
return (this.dateCreated == default(DateTime))
? this.dateCreated = DateTime.Now
: this.dateCreated;
}
set { this.dateCreated = value; }
}
private DateTime dateCreated = default(DateTime);
How you deal with this at the moment depends on what model you are using Linq to SQL or EntityFramework?
In L2S you can add
public partial class NWDataContext
{
partial void InsertCategory(Category instance)
{
if(Instance.Date == null)
Instance.Data = DateTime.Now;
ExecuteDynamicInsert(instance);
}
}
EF is a little more complicated see http://msdn.microsoft.com/en-us/library/cc716714.aspx for more info on EF buisiness logic.
I know this post is a little old, but a have a suggestion that may help some.
I used an Enum to determine what to set in the attribute constructor.
Property declaration :
[DbProperty(initialValue: EInitialValue.DateTime_Now)]
public DateTime CreationDate { get; set; }
Property constructor :
Public Class DbProperty Inherits System.Attribute
Public Property InitialValue As Object
Public Sub New(ByVal initialValue As EInitialValue)
Select Case initialValue
Case EInitialValue.DateTime_Now
Me.InitialValue = System.DateTime.Now
Case EInitialValue.DateTime_Min
Me.InitialValue = System.DateTime.MinValue
Case EInitialValue.DateTime_Max
Me.InitialValue = System.DateTime.MaxValue
End Select
End Sub
End Class
Enum :
Public Enum EInitialValue
DateTime_Now
DateTime_Min
DateTime_Max
End Enum
I think you can do this using StoreGeneratedPattern = Identity (set in the model designer properties window).
I wouldn't have guessed that would be how to do it, but while trying to figure it out I noticed that some of my date columns were already defaulting to CURRENT_TIMESTAMP() and some weren't. Checking the model, I see that the only difference between the two columns besides the name is that the one getting the default value has StoreGeneratedPattern set to Identity.
I wouldn't have expected that to be the way, but reading the description, it sort of makes sense:
Determines if the corresponding column in the database will be auto-generated during insert and update operations.
Also, while this does make the database column have a default value of "now", I guess it does not actually set the property to be DateTime.Now in the POCO. This hasn't been an issue for me as I have a customized .tt file that already sets all of my date columns to DateTime.Now automatically (it's actually not hard to modify the .tt file yourself, especially if you have ReSharper and get a syntax highlighting plugin. (Newer versions of VS may already syntax highlight .tt files, not sure.))
The issue for me was: how do I get the database column to have a default so that existing queries that omit that column will still work? And the above setting worked for that.
I haven't tested it yet but it's also possible that setting this will interfere with setting your own explicit value. (I only stumbled upon this in the first place because EF6 Database First wrote the model for me this way.)
below works in .NET 5.0
private DateTime _DateCreated= DateTime.Now;
public DateTime DateCreated
{
get
{
return this._DateCreated;
}
set { this._DateCreated = value; }
}
You can also consider using the DatabaseGenerated attribute, example
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public DateTime DateCreated { get; set; }
https://learn.microsoft.com/en-us/ef/core/modeling/generated-properties?tabs=data-annotations
I also wanted this and came up with this solution (I'm only using the date part - a default time makes no sense as a PropertyGrid default):
public class DefaultDateAttribute : DefaultValueAttribute {
public DefaultDateAttribute(short yearoffset)
: base(DateTime.Now.AddYears(yearoffset).Date) {
}
}
This just creates a new attribute that you can add to your DateTime property.
E.g. if it defaults to DateTime.Now.Date:
[DefaultDate(0)]
How do you give a C# auto-property an initial value?
I either use the constructor, or revert to the old syntax.
Using the Constructor:
class Person
{
public Person()
{
Name = "Initial Name";
}
public string Name { get; set; }
}
Using normal property syntax (with an initial value)
private string name = "Initial Name";
public string Name
{
get
{
return name;
}
set
{
name = value;
}
}
Is there a better way?
In C# 5 and earlier, to give auto implemented properties an initial value, you have to do it in a constructor.
Since C# 6.0, you can specify initial value in-line. The syntax is:
public int X { get; set; } = x; // C# 6 or higher
DefaultValueAttribute is intended to be used by the VS designer (or any other consumer) to specify a default value, not an initial value. (Even if in designed object, initial value is the default value).
At compile time DefaultValueAttribute will not impact the generated IL and it will not be read to initialize the property to that value (see DefaultValue attribute is not working with my Auto Property).
Example of attributes that impact the IL are ThreadStaticAttribute, CallerMemberNameAttribute, ...
Edited on 1/2/15
C# 6 :
With C# 6 you can initialize auto-properties directly (finally!), there are now other answers that describe that.
C# 5 and below:
Though the intended use of the attribute is not to actually set the values of the properties, you can use reflection to always set them anyway...
public class DefaultValuesTest
{
public DefaultValuesTest()
{
foreach (PropertyDescriptor property in TypeDescriptor.GetProperties(this))
{
DefaultValueAttribute myAttribute = (DefaultValueAttribute)property.Attributes[typeof(DefaultValueAttribute)];
if (myAttribute != null)
{
property.SetValue(this, myAttribute.Value);
}
}
}
public void DoTest()
{
var db = DefaultValueBool;
var ds = DefaultValueString;
var di = DefaultValueInt;
}
[System.ComponentModel.DefaultValue(true)]
public bool DefaultValueBool { get; set; }
[System.ComponentModel.DefaultValue("Good")]
public string DefaultValueString { get; set; }
[System.ComponentModel.DefaultValue(27)]
public int DefaultValueInt { get; set; }
}
When you inline an initial value for a variable it will be done implicitly in the constructor anyway.
I would argue that this syntax was best practice in C# up to 5:
class Person
{
public Person()
{
//do anything before variable assignment
//assign initial values
Name = "Default Name";
//do anything after variable assignment
}
public string Name { get; set; }
}
As this gives you clear control of the order values are assigned.
As of C#6 there is a new way:
public string Name { get; set; } = "Default Name";
Sometimes I use this, if I don't want it to be actually set and persisted in my db:
class Person
{
private string _name;
public string Name
{
get
{
return string.IsNullOrEmpty(_name) ? "Default Name" : _name;
}
set { _name = value; }
}
}
Obviously if it's not a string then I might make the object nullable ( double?, int? ) and check if it's null, return a default, or return the value it's set to.
Then I can make a check in my repository to see if it's my default and not persist, or make a backdoor check in to see the true status of the backing value, before saving.
In C# 6.0 this is a breeze!
You can do it in the Class declaration itself, in the property declaration statements.
public class Coordinate
{
public int X { get; set; } = 34; // get or set auto-property with initializer
public int Y { get; } = 89; // read-only auto-property with initializer
public int Z { get; } // read-only auto-property with no initializer
// so it has to be initialized from constructor
public Coordinate() // .ctor()
{
Z = 42;
}
}
Starting with C# 6.0, We can assign default value to auto-implemented properties.
public string Name { get; set; } = "Some Name";
We can also create read-only auto implemented property like:
public string Name { get; } = "Some Name";
See: C# 6: First reactions , Initializers for automatically implemented properties - By Jon Skeet
In Version of C# (6.0) & greater, you can do :
For Readonly properties
public int ReadOnlyProp => 2;
For both Writable & Readable properties
public string PropTest { get; set; } = "test";
In current Version of C# (7.0), you can do : (The snippet rather displays how you can use expression bodied get/set accessors to make is more compact when using with backing fields)
private string label = "Default Value";
// Expression-bodied get / set accessors.
public string Label
{
get => label;
set => this.label = value;
}
In C# 9.0 was added support of init keyword - very useful and extremly sophisticated way for declaration read-only auto-properties:
Declare:
class Person
{
public string Name { get; init; } = "Anonymous user";
}
~Enjoy~ Use:
// 1. Person with default name
var anonymous = new Person();
Console.WriteLine($"Hello, {anonymous.Name}!");
// > Hello, Anonymous user!
// 2. Person with assigned value
var me = new Person { Name = "#codez0mb1e"};
Console.WriteLine($"Hello, {me.Name}!");
// > Hello, #codez0mb1e!
// 3. Attempt to re-assignment Name
me.Name = "My fake";
// > Compilation error: Init-only property can only be assigned in an object initializer
In addition to the answer already accepted, for the scenario when you want to define a default property as a function of other properties you can use expression body notation on C#6.0 (and higher) for even more elegant and concise constructs like:
public class Person{
public string FullName => $"{First} {Last}"; // expression body notation
public string First { get; set; } = "First";
public string Last { get; set; } = "Last";
}
You can use the above in the following fashion
var p = new Person();
p.FullName; // First Last
p.First = "Jon";
p.Last = "Snow";
p.FullName; // Jon Snow
In order to be able to use the above "=>" notation, the property must be read only, and you do not use the get accessor keyword.
Details on MSDN
In C# 6 and above you can simply use the syntax:
public object Foo { get; set; } = bar;
Note that to have a readonly property simply omit the set, as so:
public object Foo { get; } = bar;
You can also assign readonly auto-properties from the constructor.
Prior to this I responded as below.
I'd avoid adding a default to the constructor; leave that for dynamic assignments and avoid having two points at which the variable is assigned (i.e. the type default and in the constructor). Typically I'd simply write a normal property in such cases.
One other option is to do what ASP.Net does and define defaults via an attribute:
http://msdn.microsoft.com/en-us/library/system.componentmodel.defaultvalueattribute.aspx
My solution is to use a custom attribute that provides default value property initialization by constant or using property type initializer.
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
public class InstanceAttribute : Attribute
{
public bool IsConstructorCall { get; private set; }
public object[] Values { get; private set; }
public InstanceAttribute() : this(true) { }
public InstanceAttribute(object value) : this(false, value) { }
public InstanceAttribute(bool isConstructorCall, params object[] values)
{
IsConstructorCall = isConstructorCall;
Values = values ?? new object[0];
}
}
To use this attribute it's necessary to inherit a class from special base class-initializer or use a static helper method:
public abstract class DefaultValueInitializer
{
protected DefaultValueInitializer()
{
InitializeDefaultValues(this);
}
public static void InitializeDefaultValues(object obj)
{
var props = from prop in obj.GetType().GetProperties()
let attrs = prop.GetCustomAttributes(typeof(InstanceAttribute), false)
where attrs.Any()
select new { Property = prop, Attr = ((InstanceAttribute)attrs.First()) };
foreach (var pair in props)
{
object value = !pair.Attr.IsConstructorCall && pair.Attr.Values.Length > 0
? pair.Attr.Values[0]
: Activator.CreateInstance(pair.Property.PropertyType, pair.Attr.Values);
pair.Property.SetValue(obj, value, null);
}
}
}
Usage example:
public class Simple : DefaultValueInitializer
{
[Instance("StringValue")]
public string StringValue { get; set; }
[Instance]
public List<string> Items { get; set; }
[Instance(true, 3,4)]
public Point Point { get; set; }
}
public static void Main(string[] args)
{
var obj = new Simple
{
Items = {"Item1"}
};
Console.WriteLine(obj.Items[0]);
Console.WriteLine(obj.Point);
Console.WriteLine(obj.StringValue);
}
Output:
Item1
(X=3,Y=4)
StringValue
little complete sample:
using System.ComponentModel;
private bool bShowGroup ;
[Description("Show the group table"), Category("Sea"),DefaultValue(true)]
public bool ShowGroup
{
get { return bShowGroup; }
set { bShowGroup = value; }
}
You can simple put like this
public sealed class Employee
{
public int Id { get; set; } = 101;
}
In the constructor. The constructor's purpose is to initialized it's data members.
private string name;
public string Name
{
get
{
if(name == null)
{
name = "Default Name";
}
return name;
}
set
{
name = value;
}
}
Have you tried using the DefaultValueAttribute or ShouldSerialize and Reset methods in conjunction with the constructor? I feel like one of these two methods is necessary if you're making a class that might show up on the designer surface or in a property grid.
Use the constructor because "When the constructor is finished, Construction should be finished". properties are like states your classes hold, if you had to initialize a default state, you would do that in your constructor.
To clarify, yes, you need to set default values in the constructor for class derived objects. You will need to ensure the constructor exists with the proper access modifier for construction where used. If the object is not instantiated, e.g. it has no constructor (e.g. static methods) then the default value can be set by the field. The reasoning here is that the object itself will be created only once and you do not instantiate it.
#Darren Kopp - good answer, clean, and correct. And to reiterate, you CAN write constructors for Abstract methods. You just need to access them from the base class when writing the constructor:
Constructor at Base Class:
public BaseClassAbstract()
{
this.PropertyName = "Default Name";
}
Constructor at Derived / Concrete / Sub-Class:
public SubClass() : base() { }
The point here is that the instance variable drawn from the base class may bury your base field name. Setting the current instantiated object value using "this." will allow you to correctly form your object with respect to the current instance and required permission levels (access modifiers) where you are instantiating it.
public Class ClassName{
public int PropName{get;set;}
public ClassName{
PropName=0; //Default Value
}
}
This is old now, and my position has changed. I'm leaving the original answer for posterity only.
Personally, I don't see the point of making it a property at all if you're not going to do anything at all beyond the auto-property. Just leave it as a field. The encapsulation benefit for these item are just red herrings, because there's nothing behind them to encapsulate. If you ever need to change the underlying implementation you're still free to refactor them as properties without breaking any dependent code.
Hmm... maybe this will be the subject of it's own question later
class Person
{
/// Gets/sets a value indicating whether auto
/// save of review layer is enabled or not
[System.ComponentModel.DefaultValue(true)]
public bool AutoSaveReviewLayer { get; set; }
}
I know this is an old question, but it came up when I was looking for how to have a default value that gets inherited with the option to override, I came up with
//base class
public class Car
{
public virtual string FuelUnits
{
get { return "gasoline in gallons"; }
protected set { }
}
}
//derived
public class Tesla : Car
{
public override string FuelUnits => "ampere hour";
}
I think this would do it for ya givng SomeFlag a default of false.
private bool _SomeFlagSet = false;
public bool SomeFlag
{
get
{
if (!_SomeFlagSet)
SomeFlag = false;
return SomeFlag;
}
set
{
if (!_SomeFlagSet)
_SomeFlagSet = true;
SomeFlag = value;
}
}