C# allows the creation of a property as below:
public string SomeRandomText
{
get; set;
}
The framework handles the creation of the backing variable for this property. How can I have such a property and still have change notification?
Is this allowed in a class that implements INotifyPropertyChanged?
public string SomeRandomTextBeingNotified
{
get;
set
{
NotifyPropertyChanged("SomeRandomTextBeingNotified");
}
}
You can't use automatic properties when trying to use this. You'll need to creating a backing store:
private string _someRandomText;
public string SomeRandomText {
get { return _someRandomText; }
set
{
_someRandomText = value;
NotifyPropertyChanged("SomeRandomText");
}
}
To make code look cleaner, you can use attributes for INotifyPropertyChanged.
Easy usage of INotifyPropertyChanged with Property-Attribute
Have a look at this Use of Attributes... INotifyPropertyChanged
Actually you can, but you basically need to change the bytecode post C# compiler.
This may sound like a lot of work, but this is one of the easier postprocessing steps that for example PostSharp includes.
http://www.sharpcrafters.com/solutions/notifypropertychanged
http://www.sharpcrafters.com/blog/post/Recording-Automate-INotifyPropertyChanged-with-Karol-Waledzik-from-Internetium.aspx
A lot more functionality is available ;)
Otherwise note that
enter code hereenter code here`NotifyPropertyChanged("SomeRandomTextBeingNotified");
is bad code. I do all that in one field update method:
set
{
OnUpateField (ref _someRandomText, value);
}
The update method does all - check for equality (you do NOT want to trigger when new value = old value), then trigger updates as needed. It gets the property name through the calling method third parameter that is automatically set by the compiler. Alternatives are using a LINQ statement ( ref someRandomText, value, this->SomeRandomText). I never would love a string there that does not get renamed on refactoring ;)
If you don't have a base class, something like this is cake and very flexible:
public class NotificationObject : INotifyPropertChanged
{
private readonly Dictionary<string, object> Properties = new Dictionary<string, object>();
public event PropertyChangedEventHandler PropertyChanged;
protected TType Get<TType>(string propertyName)
{
object value;
return Properties.TryGetValue(propertyName, out value) ? (TType)value : default(TType);
}
protected void Set<TType>(TType value, string propertyName, params string[] dependantPropertyNames)
{
Properties[propertyName] = value;
OnPropertyChanged(propertyName);
if (dependantPropertyNames != null)
{
foreach (string dependantPropertyName in dependantPropertyNames)
{
OnPropertyChanged(dependantPropertyName);
}
}
}
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArts(propertyName));
}
}
}
This can be used like this:
public SomeObjectThatNeedsToNotifySomething : NotificationObject
{
public int SomeValue
{
get { return Get<int>("SomeValue"); }
set { Set<int>(value, "SomeValue", "SomeAggregateValue"); }
}
public int SomeOtherValue
{
get { return Get<int>("SomeOtherValue"); }
set { Set<int>(value, "SomeOtherValue", "SomeAggregateValue"); }
}
public int SomeAggregateValue
{
get { return SomeValue + SomeOtherValue; }
}
}
If you already have a base class and need to just implement the INotifyPropertyChanged interface, #Rob is correct, provide a backing field and fire the event.
There is no such thing as semi-automatic properties. Nevertheless, there are quite a few ways to implement INotifyPropertyChanged that don't require the burdensome imperative code.
1) Mentioned before: PostSharp, an aspect oriented and commercial project.
2) Creating a Castle DynamicProxy solution. A sample can be found here, actually there's plenty of others out there.
It's worthwhile investing some time in a generic solution, the boilerplate code can get vexing after a while and is prone to errors.
Related
This question already has answers here:
Implementing INotifyPropertyChanged - does a better way exist?
(35 answers)
Closed 1 year ago.
I've got a MVVM-ish application which ended up with a model with way too many property change notifications. Specifically, I'm sometimes missing some notifications because there's too many of them.
For example I end up with properties like this:
public string CustomEmail {
get => customEmail;
set
{
customEmail = value;
OnChanged("CustomEmail");
OnChanged("IsSendAllowed");
OnChanged("IsNotFaxEmail");
}
}
Is there a better way to organise it? For example is there a way to mark a property [DependsOn("CustomEmail")] bool IsNotFaxEmail { ... }?
Or if most of the properties are used for bindings, should I be going all in on converters instead? I'd rather not end up with a silly number of converters like {Binding CustomEmail, Converter=EmailIsFaxToElementVisibilityConverter}.
Am I missing some simpler solution?
I don't often find so many dependencies but I can outline a solution I've seen.
Create an attribute. Call it AlsoRaise attribute which takes a string parameter.
You can probably think of a better name. But I think dependson isn't quite right because it's the other way round.
[AlsoRaise(nameof(IsSendAllowed))]
[AlsoRaise(nameof(IsNotFaxEmail))]
public string CustomEmail
You then have something can drive your list of other properties you're going to raise change notification for as well as CustomEmail.
In a static constructor you fill a dictionary<string, string[]> using those attributes. You iterate public properties, grab those attributes.
In OnChanged you look up your property name in that dictionary and raise property changed for the property name plus any strings you find. Or none of course.
I may have forgotten some part, while since I saw this implementation.
You may write a NotifyPropertyChanged method that accepts multiple property names. It does not really reduce the amount of code, but at least allows to make only one method call.
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(params string[] propertyNames)
{
var propertyChanged = PropertyChanged;
if (propertyChanged != null)
{
foreach (var propertyName in propertyNames)
{
propertyChanged.Invoke(this,
new PropertyChangedEventArgs(propertyName));
}
}
}
}
public class ViewModel : ViewModelBase
{
private string customEmail;
public string CustomEmail
{
get => customEmail;
set
{
customEmail = value;
NotifyPropertyChanged(
nameof(CustomEmail),
nameof(IsSendAllowed),
nameof(IsNotFaxEmail));
}
}
}
I think PropertyChanged.Fody is exactly what you are looking for. It is a specialized library for Fody, which is a code weaving tool. It enables manipulating the IL code of an assembly on build e.g. for adding boilerplate code to classes like implementing property changed notifications.
PropertyChanged.Fody is very powerful in that it can automatically implement INotifyPropertyChanged. Below is an example from the official repository. It is all you have to write, Fody will add (weave in) the rest.
public class Person : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public string GivenNames { get; set; }
public string FamilyName { get; set; }
public string FullName => $"{GivenNames} {FamilyName}";
}
Furthermore, dependent properties like GivenNames and FamilyName in this example are detected and will notify a property change for FullName if they are changed, too. There are lots of options to configure property changed notifications manually through attributes like:
AlsoNotifyFor
DoNotNotify
DependsOn
...
These attributes are the most useful for your scenario. Your sample would be reduced to:
[AlsoNotifyFor("IsSendAllowed")]
[AlsoNotifyFor("IsNotFaxEmail")]
public string CustomEmail { get; set; }
Or the other way around with DependsOn:
[DependsOn("CustomEmail")]
public string IsSendAllowed { get; set; }
[DependsOn("CustomEmail")]
public string IsNotFaxEmail { get; set; }
For more examples and an overview of all attributes and other powerful mechanisms of Fody, have a look at the GitHub Wiki.
This question already has answers here:
Better way to trigger OnPropertyChanged
(6 answers)
Closed 6 years ago.
I want to simplify the property declarations in my classes. The problem is the getter and setter definition. I am doing exactly the same for hundreds of properties. All properties are created like this, where the method "LogPropertyChanged" also RaisePropertyChange.
public class PCS_MA_V1_ALARMSTAT : ViewModelBase
{
private Boolean _ActionAlarmHighHigh;
public Boolean ActionAlarmHighHigh
{
get
{
return _ActionAlarmHighHigh;
}
set
{
if(value!= _ActionAlarmHighHigh)
{
_ActionAlarmHighHigh = value;
LogpropertyChanged("ActionAlarmHighHigh", oldVal, newVal);
}
}
}
private Boolean _ActionAlarmLowLow;
public Boolean ActionAlarmLowLow
{
get
{
return _ActionAlarmLowLow;
}
set
{
if(value!= _ActionAlarmLowLow)
{
_ActionAlarmLowLow = value;
LogpropertyChanged("ActionAlarmLowLow", oldVal, newVal);
}
}
}
}
Now i think this syntax is much to complex, and a huge hasle to work with. Is there a way where i could create the class like this:
public class PCS_MA_V1_ALARMSTAT: ViewModelBase
{
public Boolean ActionAlarmHighHigh { get; set; }
public Boolean ActionAlarmLowLow { get; set; }
}
And then monitor the instance. If a property has changed i run LogPropertyChanged on that particular property. Is this possible?
You can't override the default behavior of get and set, unfortunately.
What you can do is write a ViewModelBase like this. It's a common idiom. My code below is mostly stolen from this answer, and Prism's BindableBase has a similar SetProperty<T> method, but I didn't go looking for their implementation. There can't be all that much to it.
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace HollowEarth.MVVM
{
public class ViewModelBase : INotifyPropertyChanged
{
#region SetProperty
protected virtual bool SetProperty<T>(ref T backingField,
T newValue,
[CallerMemberName] String propName = null)
{
if (EqualityComparer<T>.Default.Equals(backingField, newValue))
{
#if DEBUG
System.Diagnostics.Trace.WriteLine(
$"No change in {propName} == {backingField}");
#endif
return false;
}
#if DEBUG
System.Diagnostics.Trace.WriteLine(
$"Changing {propName} from {backingField} to {newValue}");
#endif
backingField = newValue;
OnPropertyChanged(propName);
return true;
}
#endregion SetProperty
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(
[CallerMemberName] String propName = null)
{
PropertyChanged?.Invoke(this,
new PropertyChangedEventArgs(propName));
}
#endregion INotifyPropertyChanged
}
}
And use it like so:
public class MyViewModel : ViewModelBase
{
#region Whenever Property
private DateTime? _whenever = default(DateTime?);
public DateTime? Whenever
{
get { return _whenever; }
set { SetProperty(ref _whenever, value); }
}
#endregion Whenever Property
}
I write Visual Studio snippets to generate properties. You said that you're generating all this stuff programmatically so snippets aren't an immediate requirement, but it's something to keep in mind.
Another possibility, if maintainability of generated code is a concern, to use partial classes. Put the generated code in separate files that are never edited by hand (much like Form1.Designer.cs/Form1.resx in winforms), and maintain the input files that are used to generate those files. Set up your generator as a build action for whatever your input files are.
For a meta-level witticism on the subject of maintainability, write the partial class generator in Perl.
Im sorry if it's a duplicate but I couldn't find the question similiar to this one.
From the stackoverflow other questions (this site is superb) I discovered how to bind XAML items to static class with event updates. It works that way:
XAML:
<Label x:Name="label_cc_CPUPOWER" Content="{Binding Path=(database:Database.CPU_CPUPOWER)}"...
Code:
public static class Database
{
#region Event firing
public static event EventHandler<PropertyChangedEventArgs> StaticPropertyChanged;
private static void NotifyStaticPropertyChanged(string propertyName)
{
if (StaticPropertyChanged != null)
StaticPropertyChanged(null, new PropertyChangedEventArgs(propertyName));
}
#endregion
//CPU
private static string _CPU_CPUCLOCK;
public static string CPU_CPUCLOCK
{
get { return _CPU_CPUCLOCK; }
set
{
if (value != _CPU_CPUCLOCK)
{
_CPU_CPUCLOCK = value;
NotifyStaticPropertyChanged("CPU_CPUCLOCK");
}
}
}
private static string _CPU_CPUPOWER;
public static string CPU_CPUPOWER
{
get { return _CPU_CPUPOWER; }
set
{
if (value != _CPU_CPUPOWER)
{
_CPU_CPUPOWER = value;
NotifyStaticPropertyChanged("CPU_CPUPOWER");
}
}
}
It works and Im really grateful to You that I don't have to figure this out all by myself BUT I have about 25-50 values to store like that. I Wonder if there's a way automate this instead of copy/paste with changing names in brackets?
I also thought about making an List for each object like CPU,RAM and just send EventChanged to the whole object but Im trying to minimize cpu usage and IMHO raising PropertyChanged to all objects while I just want to update two of five isn't good way to do that as whole object values would be refreshed.
Regards
Yes there are, check this out: PropertyChanged.Fody
Then all you have to do is to add :
using PropertyChanged;
...
[ImplementPropertyChanged]
public class MyClass
{
public object Object {get;set;}
// INotifyPropertyChanged implemented automatically # compile-time
}
I've recently started experimenting with DataBinding and implementing DependencyProperties for my custom classes. It all works fine and the possibilities are exciting, however, I came across a problem that may be only solvable by slightly modifying the overall class design. And I want to make sure this is the only option and I'm not missing anything.
So, my class stores information about video files the user imports into the application. Among other properties, it contains:
public class VideoFile {
public string FilePath { get; protected set; }
public uint ID { get; protected set; ]
public string Extension { get { return Path.GetExtension(FilePath); } }
public string FileName { get { return Path.GetFilename(FilePath); } }
}
So, I've successfully replaced FilePath with an DependencyProperty. However, in the UI, I mostly want to display just the filename, which uses some logic to provide its value. As far as I know, here are my options:
I could simply create DependencyProperties for FileName and Extension, and set their value in the constructor, but that's redundant; I already have that information in the FilePath, so I want to avoid this option.
Create ValueConverters, one for displaying Filename and one for displaying Extension, and use them in my bindings.
I've only met ValueConverters briefly, so I'm not sure about it. Can I use them for this purpose? Or, have I just encountered one of the main reasons they exist? :)
And last but not least, can anyone think of a situation similar to this, when a ValueConverter is not the right way to go? I want to avoid jumping straight into them, only to realize it will not work because "that one" property just can't be expressed in this way.
You don't need DependencyProperties for this. You only need a DependencyProperty when you're going to set into a property using a MarkupExtension, and I doubt you're doing that with a model class (because you won't be declaring this class in Xaml!).
A much more lightweight way would be to use INotifyPropertyChanged. Here's a .NET 3.5-style implementation:
public class VideoFile : INotifyPropertyChanged
{
private string _filePath;
public string FilePath
{
get
{
return _filePath;
}
protected set
{
_filePath = value;
OnPropertyChanged("FilePath");
OnPropertyChanged("Extension");
OnPropertyChanged("FileName");
}
}
public uint ID { get; protected set; }
public string Extension { get { return Path.GetExtension(FilePath); } }
public string FileName { get { return Path.GetFileName(FilePath); } }
protected void OnPropertyChanged(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
(In .NET 4.5 this can be simplified somewhat thanks to the new [CallerMemberName] attribute.)
The only downside is that you require backing fields for your properties. However, there's a VS extension called NotifyPropertyWeaver that can automate part of this work and remove the need for explicit backing properties, too.
Don't duplicate data.
Prefer Binding and an IValueConverter, because that way, whenever FilePath changes, Extension and FileName will be updated in the UI as well.
You could also, of course, raise PropertyChanged for them in FilePath's setter but that's bad practice since FilePath should not have to care about who/what uses it.
The class then looks like:
public class VideoFile : INotifyPropertyChanged {
string m_FilePath;
public string FilePath
{
get { return m_FilePath; }
protected set
{
if(value != m_FilePath)
{
m_FilePath = value;
RaisePropertyChanged(() => this.FilePath);
}
}
}
public uint ID { get; protected set; }
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChanged<T>(Expression<Func<T>> _PropertyExpression)
{
RaisePropertyChanged(PropertySupport.ExtractPropertyName(_PropertyExpression));
}
protected void RaisePropertyChanged(String _Prop)
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(_Prop));
}
}
#endregion
}
Please note that PropertySupport is part of Prism, but you can do without it by calling RaisePropertyChanged("FilePath"), it's just neat to have type safety because if you change the property's name you will have a compile-time error.
As far as I understand you would like to just display File Name on UI. Then you may consider updating FileName property whenever FilePath dependency property is changed (OnChangedFilePath method). You can also check if FilePath is OK in ValidateFilePath method. Please note that FileName must be also a dependency property or supporting IPropertyChanged, otherwise UI will not be updated when you change it. You do not need to use a converter for this purpose.
public string FilePath
{
get { return (string)GetValue(FilePathProperty); }
set { SetValue(FilePathProperty, value); }
}
private static object CoerceFilePath(DependencyObject d, object value)
{
return value;
}
private static bool ValidateFilePath(object Value)
{
return true;
}
private static void OnChangedFilePath(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
}
public static readonly DependencyProperty FilePathProperty =
DependencyProperty.Register("FilePath", typeof(string), typeof(ClassName),
new PropertyMetadata(#"C:\File.avi", OnChangedFilePath, CoerceFilePath),
new ValidateValueCallback(ClassName.ValidateFilePath));
I have a class Application that I need to override with INotifyPropertyChanged events. I have written the logic to override the original class and ended up creating SuperApplication
I am pulling the data from a library though, and cannot change the loading logic. I just need a way to get the data from the original class into my superClass. I've tried things like superClass = (SuperApplication)standardClass; but it hasn't worked.
How would I go about doing this?
If it helps, this is the code I'm using to override the original class:
public class SuperCreditApplication : CreditApplication
{
public SuperCreditApplicant Applicant { get; set; }
public SuperCreditApplicant CoApplicant { get; set; }
}
public class SuperCreditApplicant : CreditApplicant
{
public SuperProspect Prospect { get; set; }
}
public class SuperProspect : Prospect, INotifyPropertyChanged
{
public State DriverLicenseState
{
get
{
return DriverLicenseState;
}
set
{
DriverLicenseState = value;
OnPropertyChanged("DriverLicenseState");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
It sounds like you should use a copy constructor, passing in "the data from the original class" as a parameter to a newly-constructed superClass (Incidentally, I think the name Super- is probably a mistake, as that will make people think that it's above the original in the hierarchy).
By copy-constructor, I mean something like:
class IWishIWasntCalledSuperApplication : Application
{
IWishIWasntCalledSuperApplication(Application original)
{
this.someData = original.someData;
this.someOtherData = original.someOtherData;
...etc...
}
}
I assume that you can't just implement INotifyPropertyChanged directly on Prospect. If you cannot directly change Prospect (like make all your properties virtual), you can make your SuperProspect class a wrapper for Prospect
public class SuperProspect : INotifyPropertyChanged
{
private readonly Prospect _prospect;
public SuperProspect(Prospect prospect)
{
_prospect = prospect;
}
public State DriverLicenseState
{
get { return _prospect.DriverLicenseState; }
set
{
_prospect.DriverLicenseState = value;
OnPropertyChanged("DriverLicenseState");
}
}
public void SomeMethod()
{
_prospect.SomeMethod();
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
You can then use SuperProspect like this
var superProspect = new SuperProspect(myProspect);
If you create an interface for your Prospect members, then you can make both your SuperProspect and your Prospect implement the same interface. If you then program to the interface rather than the concrete Prospect implementation, your code will work with both SuperProspect and/or Prospect.
You didn't say whether the load was during the construction of the object or a later method call. Depending on which, it would look like one of these two code samples.
//This constructor signature should match your base class's
public SuperCreditApplication(object a, object b, object c) : base(a,b,c)
{
//Do whatever you need to do here. The base object's constructor will be called for you
}
public Load()
{
this.BaseObjectLoadMethod();
}
Then you make a new SuperCreditApplication and work with that.
Given your comment and edit I need to give a new answer lol - i misunderstood
you need to use interception to add the event handlers to the properties over which you have no control maybe. Personally I ahve seen this done with IoC containers such as prism. I may be completley wrong here btw but i think MEF may also help
Another way would be to look into code generation using T4 templates to reflect over the existing class to generate your superclass and the properties that map onto 4existing that would contain the code to fire the events.
this looks like it
http://lostechies.com/derekgreer/2009/03/01/implementing-inotifyproperychanged-with/
To explain the MEF thing: I am pretty sure i have seen INotifyPropertyChanged hooked up using MEF in various silverlight examples. I wasn't interested in that aspect when i was reading though so didn't read up on it.
Extracting an interface and using an ioc container to do all the heavy lifting would be the shortest route i imagine.