How to implement INotifyPropertyChanged

Question

I need help implementing INotifyPropertyChanged in my own data structure class. This is for a class assignment, but implementing INotifyPropertyChanged is an addition that I am doing above and beyond what the rubric requires.

I have a class named 'BusinessRules' that uses a SortedDictionary to store objects of 'Employee' type. I have a DataGridView showing all of my employees, and I want to use my BusinessRules class object as the DataSource for my DataGridView. The BusinessRules container is required for the assignment. I have tried to implement INotifyPropertyChanged in this class, with no success.

The DataSource that I have working is a BindingList. Presently, I am using that BindingList as a 'sidecar' container and setting that as my DataSource. Every change that I make to my BusinessRules class object is mirrored to my BindingList class object. But this is obviously sloppy programming, and I want to do better.

I have tried to implement INotifyPropertyChanged in BusinessRules, but when I set my instantiated BusinessRules object as the DataSource, the DataGridView shows nothing. What I suspect the problem to be is with the NotifyPropertyChanged() method. I do not know what to pass to this, nor what to do with what is passed in. Most examples deal with changing a name, but I am more concerned when a new object is added to the SortedDictionary.

 private void NotifyPropertyChanged( Employee emp ) { PropertyChanged?.Invoke( this, new PropertyChangedEventArgs( emp.FirstName ) ); }

What do I need to change in order to get this working? Will you explain why my attempt is not working?

I am notoriously bad about forming my questions on StackOverflow. This is not intentional. Please, let me know what other information you require, and I will provide it as quickly as I can.

Here is a link to my BusinessRules source code.

jegtugado · Accepted Answer · 2016-10-12 06:06:22Z

It will be very helpful if you read tutorials on how to implement MVVM.

You'd wanna have a base class that implements INotifyPropertyChanged interface. So all your view models should inherit from this base class.

public class ViewModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; protected void RaisePropertyChangedEvent(string propertyName) { var handler = PropertyChanged; if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName)); } } // This sample class DelegateCommand is used if you wanna bind an event action with your view model public class DelegateCommand : ICommand { private readonly Action _action; public DelegateCommand(Action action) { _action = action; } public void Execute(object parameter) { _action(); } public bool CanExecute(object parameter) { return true; } #pragma warning disable 67 public event EventHandler CanExecuteChanged; #pragma warning restore 67 }

Your view model should look like this.

public sealed class BusinessRules : ViewModelBase

Here's an example on how to utilize the RaisePropertyChangedEvent.

public sealed class Foo : ViewModelBase { private Employee employee = new Employee(); private string Name { get { return employee.Name; } set { employee.Name = value; RaisePropertyChangedEvent("Name"); // This will let the View know that the Name property has updated } } // Add more properties // Bind the button Command event to NewName public ICommand NewName { get { return new DelegateCommand(ChangeName)} } private void ChangeName() { // do something this.Name = "NEW NAME"; // The view will automatically update since the Name setter raises the property changed event } }

I don't really know what you want to do so I'll leave my example like this. Better read different tutorials, the learning curve is a bit steep.

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