INotifyPropertyChanged-更改PropertyName不会产生任何效果

我正在尝试将Winforms UI绑定到ViewModel。我能够在UI更改时成功更新ViewModel，反之亦然。然而，我似乎不明白PropertyChangedEventHandler中使用的"PropertyName"有什么用，因为无论我放在那里什么，它都会一直起作用。我不知道我是否已经把事情搞混了，因为我读了很多关于体系结构模式（MVP、MVC、MVVM和MVP-VM（这就是我现在试图做的））的文章。

以下是相关代码的一部分：

ViewModel

public class AdditionViewModel:INotifyPropertyChanged
{
    private string augend;
    public string Augend
    {
        get { return augend; }
        set { 
                if(augend != value)
                {
                    augend = value;
                    OnPropertyChanged(new PropertyChangedEventArgs("ugend"));
                }
            }
    }
    private string addend;
    public string Addend
    {
        get { return addend; }
        set {
                if (addend != value)
                {
                    addend = value;
                    OnPropertyChanged(new PropertyChangedEventArgs("ddend"));
                }
            }
    }
    private string answer;
    public string Answer
    {
        get { return answer; }
        set {
                if(answer != value)
                {
                    answer = value;
                    OnPropertyChanged(new PropertyChangedEventArgs("nswer"));
                }
            }
    }
    public AdditionClass additionClass;
    public AdditionViewModel(AdditionClass _additionClass)
    {
        additionClass = _additionClass;
    }
    public void Add()
    {
        //Some verifications first before inserting the value to the model class
        this.Augend = "1";//Testing for from code to UI binding
        additionClass.Augend = Double.Parse(Augend);
        additionClass.Addend = Double.Parse(Addend);
        //Somewhere here should implement the compute but since addition is a very simple task, no methods were called;
        Answer = additionClass.Answer.ToString();
    }
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            MessageBox.Show(e.PropertyName);
            handler(this, new PropertyChangedEventArgs(e.PropertyName));
        }
    }
}

形式：

private void Form1_Load(object sender, EventArgs e)
{
    additionPresenter = new Presenter.AdditionPresenter(new ViewModel.AdditionViewModel(new Model.AdditionClass()));
    additionViewModelBindingSource.DataSource = additionPresenter.additionViewModel;
}
private void button1_Click(object sender, EventArgs e)
{
    additionPresenter.AddButtonClick();
}

演示者：

public AdditionPresenter(AdditionViewModel _additionViewModel)
{
    additionViewModel = _additionViewModel;
}
public void AddButtonClick()
{
    additionViewModel.Add();
}

设计器自动生成的代码之一（绑定在UI上）：

// 
// textBox1
// 
this.textBox1.DataBindings.Add(new System.Windows.Forms.Binding("Text", this.additionViewModelBindingSource, "Addend", true));
this.textBox1.Location = new System.Drawing.Point(24, 41);
this.textBox1.Name = "textBox1";
this.textBox1.Size = new System.Drawing.Size(100, 20);
this.textBox1.TabIndex = 0;

正如在ViewModel上可以看到的那样，我省略了setters中每个PropertyName开头的所有"A"，但应用程序仍在工作。很抱歉粘贴了太长的代码。我似乎找不到比向您展示实现