When do we need to use [Browsable(true)]?
EDIT (by SLaks): He's asking (I assume) why one would need to pass true as the parameter, given that it's already true by default.
As far as I know, never.
EDIT
I was wrong.
It's necessary if you want to make a property which has [Browsable(false)] in your base class (such as UserControl.Text) browsable.
MSDN says it all:
Specifies whether a property or event should be displayed in a Properties window.
For example, if you're creating a User Control, you might want to decorate non-UI-related properties with [Browsable(false)] so that they will not be available through a "Properties" window.
Additionally, it controls which properties of an object can be seen in a PropertyGrid.
As for why we can pass true explicitly, I believe this is due to BrowsableAttributes property of a PropertyGrid. You can set it to contain BrowsableAttribute.No, so that the property grid will display all non-browsable members.
Probably when you want to make damn sure no one changes it :P
// I want to see this, dont change it to false or I'll hunt you down...
[Browsable(true)]
public int MyProperty {
get {
// Insert code here.
return 0;
}
set {
// Insert code here.
}
}
The problem is that things are browsable by default. The only scenario I can think where this would matter is overriding a member and changing the browsability... here F is visible only because of the [Browsable(true)] in the derived class - without it, it isn't visible.
using System.ComponentModel;
using System;
using System.Windows.Forms;
static class Program
{
[STAThread]
static void Main() {
Application.EnableVisualStyles();
Application.Run(new Form { Controls = {new PropertyGrid {
Dock = DockStyle.Fill, SelectedObject = new Bar()
}}});
}
}
public class Foo
{
public virtual string A { get; set; }
public virtual string B { get; set; }
public virtual string C { get; set; }
[Browsable(false)] public virtual string D { get; set; }
[Browsable(false)] public virtual string E { get; set; }
[Browsable(false)] public virtual string F { get; set; }
[Browsable(true)] public virtual string G { get; set; }
[Browsable(true)] public virtual string H { get; set; }
[Browsable(true)] public virtual string I { get; set; }
}
public class Bar : Foo
{
public override string A { get { return base.A; } set { base.A = value; } }
[Browsable(false)] public override string B { get { return base.B; } set { base.B = value; } }
[Browsable(true)] public override string C { get { return base.C; } set { base.C = value; } }
public override string D { get { return base.D; } set { base.D = value; } }
[Browsable(false)] public override string E { get { return base.E; } set { base.E = value; } }
[Browsable(true)] public override string F { get { return base.F; } set { base.F = value; } }
public override string G { get { return base.G; } set { base.G = value; } }
[Browsable(false)] public override string H { get { return base.H; } set { base.H = value; } }
[Browsable(true)] public override string I { get { return base.I; } set { base.I = value; } }
}
BrowsableAttribute Class (System.ComponentModel)
The documentation states:
A visual designer typically displays
in the Properties window those members
that either have no browsable
attribute or are marked with the
BrowsableAttribute constructor's
browsable parameter set to true.
[Browsable] also defaults to true.
...so technically, you never need [Browsable(true)] unless you want to be very explicit.
One occassion when this attribute becomes important is during WebPart development for Sharepoint. In this scenario you are providing meta information for Sharepoint to determine whether your webpart should be viewable for selection etc. There are other similiar attributes such as Category and FriendlyName etc which are also taken into account.
See the following for examples:
Creating a web part with custom properties
And another with decent images of the sharepoint webpart editor which reflects your attributes:
Making Sharepoint WebParts interact
The types and attributes in ComponentModel are not specifically tied to any particular designer. Although I don't know of any specific scenario that you would need to "opt in" to being designer-browsable, I suppose it's conceivable that you could have some component designer that would assume browsable(false).
I suppose you could also override a virtual property that specified browsable(false) and apply browsable(true) in the overridden member.
A visual designer typically displays in the Properties window those members that either have no browsable attribute or are marked with the BrowsableAttribute constructor's browsable parameter set to true. These members can be modified at design time. Members marked with the BrowsableAttribute constructor's browsable parameter set to false are not appropriate for design-time editing and therefore are not displayed in a visual designer. The default is true.
so, the answer is you never have to, as it is done by default.
According to the documentation you want it to be true when it should be displayed in the property window in VS. Basically it applies to classes that are used in the designer.
Related
I am learning C# and i have encounter the following piece of code
public class Album
{
public virtual int AlbumId { get; set; }
public virtual int GenreId { get; set; }
public virtual int ArtistId { get; set; }
public virtual string Title { get; set; }
public virtual decimal Price { get; set; }
public virtual string AlbumArtUrl { get; set; }
public virtual Genre Genre { get; set; }
public virtual Artist Artist { get; set; }
}
just wondering what's the different with the following? i mean without the get and set you can access those public property as well. what's make it important to have those get and set?
public class Album
{
public virtual int AlbumId;
public virtual int GenreId;
public virtual int ArtistId;
public virtual string Title;
public virtual decimal Price;
public virtual string AlbumArtUrl;
public virtual Genre Genre;
public virtual Artist Artist;
}
To have control over your object private fields values. for example if you don't wanna allow nulls or negative values for integers.
bool started;
public bool Started
{
get { return started; }
set
{
started = value;
if (started)
OnStarted(EventArgs.Empty);
}
}
another example
int positiveNumber;
public int PositiveNumber
{
get { return positiveNumber; }
set {
if (value < 0)
positiveNumber = 0;
else positiveNumber = value;
}
}
and also another implementation of read only properties could be as follows
int positiveNumber;
public int PositiveNumber
{
get { return positiveNumber; }
}
You can't declare a virtual field
public class Album
{
public virtual int AlbumId; // <- Syntax error
...
}
properties are, in fact, methods: get or(and) set, so
public class Album
{
public virtual int AlbumId { get; set; } // <- Both get and set methods declared as virtual ones
...
}
And you can override these get's or(and) set's in derived class if you want:
public class GreatAlbum: Album {
private Boolean m_IsGreat;
public override int AlbumId {
get {
if (m_IsGreat)
return base.AlbumId
else
return 0;
}
set {
m_IsGreat = (value != 0);
base.AlbumId = value;
}
}
...
}
With providing get(accessor) and set(mutator) methods, you can control accessing and mutating.
For example:
You have a property that you don't want to be set any value more than 15. So u make required restrictions in your set method. Unless that set method, you can't control.
But in your example, your get and set methods are default, means controlling nothing.
The main reason behind properties is to protecting and presenting private data in a controlled way.
In fact, properties show their abilties in the usage like this:
public virtual int AlbumId
{
get { // ... some magical operations ... }
set { // ... some magical operations ... }
}
And about your main question - what's the difference in this example - the main point to attention is the virtual keyword.
This keyword causes the property to be overrideable, So any other code could override the default get; method. It meens that you have the default behavior for yourself, and other codes (Extremely used in Entity Framework) implement their own logic!
Those second ones in your example aren't properties, so they don't express this magical ability...!
In the first case you are dealing with properties, in the second with fields.
Using fields has several drawbacks when compared to using properties. These drawbacks include:
You can set a breakpoint in a get or set of a property, but you can not set a breakpoint on access to the field.
Making fields public violates the information hiding principle.
The binary MSIL code for accessing fields and properties is different, so if you change a public field to a public property in the future, although the source code stays compatible, any dependant binary code breaks.
The code required to use reflection is different, hence when you move from a field to a property, your reflection code will break.
To cut a long story short: Always use public properties, NEVER use public fields.
There are a number of differences:
Properties are turned into methods by the compiler. As such, you can declare them virtual and override them in a derived class.
Using properties, you can put logic in the getter or setter (filtering, validation etc).
When you use automatically implemented properties ({ get;set;}), it may seem that you might as well just use public fields. However, using properties means you can change your getter or setter implementation at a later time, without changing the interface your class is exposing. If you had used a field and wanted to implement filtering whenever that field was read, you would have to introduce a new method, make the field private and break all existing consumers of the type.
Personally, I think the automatically implemented properties promote bad style, because they do not encourage encapsulation. Tools like ReSharper also like to generate properties with {get;set} accessors. Novice developers thus typically end up with classes with lots of {get;set;} properties exposing the type's state to the world. You should at least use {get; private set;} by default.
Say I have a class
class Object
{
Vector2 positon;
}
This position is editable in the propert grid, how would I be able to set this as not browasable / read only in a class that inherits from object. I know the [Browsable(false)] and [ReadOnly(true)] tags but this will set the it for all Objects, which I do not desire.
Declare position property as virtual and override it on derived types.
public class Class1
{
public virtual string Lol { get; set; }
}
class Class1Impl1 : Class1
{
[Browsable(false)]
[ReadOnly(false)]
public override string Lol
{
get
{
return base.Lol;
}
set
{
base.Lol = value;
}
}
}
class Class1Impl2 : Class1
{
[Browsable(true)]
[ReadOnly(true)]
public override string Lol
{
get
{
return base.Lol;
}
set
{
base.Lol = value;
}
}
}
Doing it at runtime is a different question, IsBrowsable and IsReadOnly are readonly properties. You should google to know if there is posible to change the instances of this attributes at runtime, which I think is not.
I don't think it's possible to change the browseable attribute at runtime (and I don't understand the point of doing that), but you can have a method check your conditions and allow/disallow writing of the property. If that's good enough, I'll be glad to mock something up if you want.
EDIT:
class SomeClass
{
private Object _foo;
private Object _bar;
public Object Foo
{
get
{
return _foo;
}
set
{
if (_bar != _foo) // replace with your test
{
_foo = value;
}
}
}
}
I'm trying to add a nested property to my custom control using a TypeConverter, here is my test code:
public class TestNestedOptionConverter : TypeConverter
{
public override PropertyDescriptorCollection GetProperties(ITypeDescriptorContext context,
object value, Attribute[] filter)
{
return TypeDescriptor.GetProperties(typeof(TestNestedOption));
}
public override bool GetPropertiesSupported(ITypeDescriptorContext context)
{
return true;
}
}
[TypeConverter(typeof(TestNestedOptionConverter))]
public class TestNestedOption
{
bool test1 = false;
[Description("TestParam1")]
public bool Test1
{
get { return test1; }
set { test1 = value; }
}
[Description("TestParam2")]
public int Test2 { get; set; }
}
public partial class UserControl1 : UserControl
{
public TestNestedOption TestOption { get; set; }
public UserControl1()
{
InitializeComponent();
}
}
When I add the control to a form, I see the TestOption property in the designer property grid, but the sub-properties do not show up at all (there isn't even an expansion box next to TestOption).
My understanding of this is that it is supposed to sort of recursively call the GetProperties() method on each property, so as a test hack I put a MessageBox.Show() in the TestNestedOptionConverter.GetProperties() method, and I don't see the message when the designer loads the control. This makes me think that the overridden GetProperties() is never being called by the designer for some reason.
Any ideas about what I am doing wrong?
I'm using Visual Studio 2008.
It can't display properties for the object because the object is null. Try simply creating a new object in the UserControl1 constructor:
public partial class UserControl1 : UserControl
{
public TestNestedOption TestOption { get; set; }
public UserControl1()
{
InitializeComponent();
TestOption = new TestNestedOption();
}
}
Also, rather than writing a custom TypeConverter for this, you can just use ExpandableObjectConverter, which does exactly what you've written. If you need to override other methods, you still may want to inherit from it.
I have a class, SerializableColor, to allow me to XML serialize Colors.
public class SerializableColor
{
// omitted constructors, etc. ...
[XmlIgnore]
public Color Color
{
get { return Color.FromArgb(this.Alpha, this.Red, this.Green, this.Blue); }
set
{
this.Alpha = value.A;
this.Red = value.R;
this.Green = value.G;
this.Blue = value.B;
}
}
public int Alpha { get; set; }
public int Red { get; set; }
public int Green { get; set; }
public int Blue { get; set; }
}
Now, for example, consider a class Foo:
public class Foo
{
public SerializableColor SColor { get; set; }
}
I want to databind some WinForm Control properties to this class.
When I first add the databinding, everything works fine, but any changes are not correctly propogated.
For example, if I bind a Control's BackColor to SColor, the BackColor will be correctly updated, etc. However, if I then go and change the BackColor, the change will not be propogated to the Foo object's SColor. And if I change the Foo object's SColor, the change will not be seen on the Control's BackColor.
Databinding to a plain Color property works as desired. Just not to a SerializableColor.
Where am I going wrong?
You need to make your SerializableColor class implement INotifyPropertyChanged.
You should also make Foo implement it if SColor is changed to a new color instance entirely.
Also, you should really implement a TypeConverter if you want Windows Forms to be able to bi-directionally convert to/from your SerializedColor type.
I would like to add attributes to Linq 2 Sql classes properties. Such as this Column is browsable in the UI or ReadOnly in the UI and so far.
I've thought about using templates, anybody knows how to use it? or something different?
Generally speaking, would do you do to address this issue with classes being code-generated?
You can take advantage of the new Metadata functionality in the System.ComponentModel.DataAnnotations which will allow us to separate the MetaData from the existing domain model.
For example:
[MetadataType (typeof (BookingMetadata))]
public partial class Booking
{
// This is your custom partial class
}
public class BookingMetadata
{
[Required] [StringLength(15)]
public object ClientName { get; set; }
[Range(1, 20)]
public object NumberOfGuests { get; set; }
[Required] [DataType(DataType.Date)]
public object ArrivalDate { get; set; }
}
As requested, here's an approach using a CustomTypeDescriptor to edit the attributes at run-time; the example here is win-forms, but it should be pretty simple to swap it into WPF to see if it works...
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
// example POCO
class Foo {
static Foo()
{ // initializes the custom provider (the attribute-based approach doesn't allow
// access to the original provider)
TypeDescriptionProvider basic = TypeDescriptor.GetProvider(typeof(Foo));
FooTypeDescriptionProvider custom = new FooTypeDescriptionProvider(basic);
TypeDescriptor.AddProvider(custom, typeof(Foo));
}
public string Name { get; set; }
public DateTime DateOfBirth { get; set; }
}
// example form
static class Program {
[STAThread]
static void Main() {
Application.EnableVisualStyles();
Application.Run( new Form {
Controls = {
new DataGridView {
Dock = DockStyle.Fill,
DataSource = new BindingList<Foo> {
new Foo { Name = "Fred", DateOfBirth = DateTime.Today.AddYears(-20) }
}
}
}
});
}
}
class FooTypeDescriptionProvider : TypeDescriptionProvider
{
ICustomTypeDescriptor descriptor;
public FooTypeDescriptionProvider(TypeDescriptionProvider parent) : base(parent) { }
public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance)
{ // swap regular descriptor for bespoke (Foo) descriptor
if (descriptor == null)
{
ICustomTypeDescriptor desc = base.GetTypeDescriptor(typeof(Foo), null);
descriptor = new FooTypeDescriptor(desc);
}
return descriptor;
}
}
class FooTypeDescriptor : CustomTypeDescriptor
{
internal FooTypeDescriptor(ICustomTypeDescriptor parent) : base(parent) { }
public override PropertyDescriptorCollection GetProperties()
{ // wrap the properties
return Wrap(base.GetProperties());
}
public override PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{ // wrap the properties
return Wrap(base.GetProperties(attributes));
}
static PropertyDescriptorCollection Wrap(PropertyDescriptorCollection properties)
{
// here's where we have an opportunity to swap/add/remove properties
// at runtime; we'll swap them for pass-thru properties with
// edited atttibutes
List<PropertyDescriptor> list = new List<PropertyDescriptor>(properties.Count);
foreach (PropertyDescriptor prop in properties)
{
// add custom attributes here...
string displayName = prop.DisplayName;
if (string.IsNullOrEmpty(displayName)) displayName = prop.Name;
list.Add(new ChainedPropertyDescriptor(prop, new DisplayNameAttribute("Foo:" + displayName)));
}
return new PropertyDescriptorCollection(list.ToArray(), true);
}
}
class ChainedPropertyDescriptor : PropertyDescriptor
{
// this passes all requests through to the underlying (parent)
// descriptor, but has custom attributes etc;
// we could also override properties here...
private readonly PropertyDescriptor parent;
public ChainedPropertyDescriptor(PropertyDescriptor parent, params Attribute[] attributes)
: base(parent, attributes)
{
this.parent = parent;
}
public override bool ShouldSerializeValue(object component) { return parent.ShouldSerializeValue(component); }
public override void SetValue(object component, object value) { parent.SetValue(component, value); }
public override object GetValue(object component) { return parent.GetValue(component); }
public override void ResetValue(object component) { parent.ResetValue(component); }
public override Type PropertyType {get { return parent.PropertyType; } }
public override bool IsReadOnly { get { return parent.IsReadOnly; } }
public override bool CanResetValue(object component) {return parent.CanResetValue(component);}
public override Type ComponentType { get { return parent.ComponentType; } }
public override void AddValueChanged(object component, EventHandler handler) {parent.AddValueChanged(component, handler); }
public override void RemoveValueChanged(object component, EventHandler handler) { parent.RemoveValueChanged(component, handler); }
public override bool SupportsChangeEvents { get { return parent.SupportsChangeEvents; } }
}
You may want to consider using Damien Guard's T4 templates for Linq To Sql. Modifying his templates would most likely give you the results you seek.
Hope this helps!
This is a common problem with code-generation; while you can add members and class level attributes via an additional partial class, you can't add attributes to the generated members. To compensate, some attribute-based mechanisms allow you to specify the attributes at the class (naming the member), but not any of the ones you cite.
One hardcore option would be to write a TypeDescriptionProvider that supplies custom PropertyDescriptor definitions for the properties. This would allow you to fully control the metadata used by UI binding tools like PropertyGrid, DataGridView, etc.
However, this is possibly too much work simply to set a few UI propertiex if you can also set them by hand! But if you are interested in pursuing that option, let me know - it is a familiar area to me, but too much code to write an example if you don't want it.
Note: if you are using PropertyGrid, then you can't set the properties by hand, but you can write a TypeConverter, which is a bit less work than a full TypeDescriptionProvider; just inherit from ExpandableObjectConverter and override GetProperties(). You'll still need a shim PropertyDescriptor, so still not trivial...
You can use a partial class to make your entity implement a interface that declares the same properties of your entity and then put the attributes on the interface.
This way you can use the interface type to get the attributes from the properties.
I don't know if you will be able to use the attributes this way, but you can try something like that.
Example:
public interface IConcept {
long Code { get; set; }
[Unique]
string Name { get; set; }
bool IsDefault { get; set; }
}
public partial class Concept : IConcept { }
[Table(Name="dbo.Concepts")]
public partial class Concept
{
//...
}
You can also write/use another code generator in place of the default MSLinqToSQLGenerator.
One option to start from is this one.
I built my own, according to my needs. I don't know if there is a way to indicate which attributes must be placed in each property using the DBML Designer, or xml file, but maybe you can find a way to use this alternative to help you with your problem.