C# WPF INotifyPropertyChanged 未更新表单

Question

I am trying to implement a form with some calculations based on user inputs. Using the MVVM pattern, in particular INotifyPropertyChanged.

All works well when the user enters a value in a textbox, the calculation routine fires, and the form updates with the result.

However when the input is changed from codebehind, the Inotify routines fire, the calculation completes, but the bound controls don't update.

I have two problems:

1. Using pages within frames, I want to trigger a refresh when the page is changed
2. Import previously saved data that is in an Xml file. Again, the routine fires, but no update to the form's bound controls.

I have attached a condensed version of the code, but this isn't really the problem I don't think. Note I am using a singleton class.

Thanks

===============

//INotify code
using s = Calc.Models.GlobalStrings;

namespace Calc.ViewModels.INotify
{
    public class UcIOChanged : INotifyPropertyChanged
    {
        private static UcIOChanged instance;
        public UcIOChanged() { }

        //Make the class is a singleton
        public static UcIOChanged Instance
        {
            get
            {
                if (instance == null)
                {
                    instance = new UcIOChanged();
                }
                return instance;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        public string Pressure 
        { 
            get 
            { 
                return s.Pressure; 
            } 
            set 
            { 
                s.Pressure = value; OnPropertyChanged(); 
            } 
        }

        public void OnPropertyChanged()
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Pressure)));

        }
    }
}

Answer 1

Note I am using a singleton class.

There are no errors in this code. But you may be using it incorrectly. To avoid accidental usage errors, I advise you to change the implementation:

public class UcIOChanged
{
    // Hide the constructor to avoid
    // accidentally creating other instances.
    private UcIOChanged() {}

    //Make the class is a singleton
    public static UcIOChanged Instance { get; } = new UcIOChanged();

    public string Pressure
    {
        get
        {
            return s.Pressure;
        }
        set
        {
            if (!Equals(s.Pressure, value))
            {
                s.Pressure = value;
                PressureChanged?.Invoke(this, EventArgs.Empty);
            }

        }
    }

    // The event of the same name.
    // It's easier for one or two properties
    // than the INotifyPropertyChanged implementation.
    public event EventHandler PressureChanged;
}

Using:

    <TextBox Text="{Binding Pressure, Source={x:Static local:UcIOChanged.Instance}}"/>

PS Correct operation may be affected if you change s.Pressure somewhere in your code other than through an instance of UcIOChanged.Instance.
Therefore, you must ensure that this variable (property or field?) is only accessed with notification of its change.