使用INotifyPropertyChanged [英] using of INotifyPropertyChanged

问题描述

有人可以解释一下为什么在wpf中使用绑定时为什么需要使用INotifyPropertyChanged的实现吗?我可以在不实现此接口的情况下绑定属性吗?例如我有代码

Can someone explain me why need to use implementation of INotifyPropertyChanged when using binding in wpf? I can bind properties without implementation of this interface? For example i have code

public class StudentData : INotifyPropertyChanged
{
    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;
    #endregion

    void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    string _firstName = null;
    public string StudentFirstName
    {
        get
        {
            return _firstName;
        }
        set
        {
            _firstName = value;

            OnPropertyChanged("StudentFirstName");
        }
    }
}

并绑定到.xaml

<TextBox Text="{Binding Path=StudentFirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
   Grid.Row="1"
   Grid.Column="2"
   VerticalAlignment="Center" />

.xaml.cs中的这段代码

this code from .xaml.cs

StudentData _studentData = new StudentData { StudentFirstName = "John", StudentGradePointAverage = 3.5};

public MainWindow()
{
    InitializeComponent();

    this.DataContext = _studentData;
}

为什么在这种情况下需要使用INotifyPropertyChanged?这不是我的代码.

why we need to use INotifyPropertyChanged in this case? It is not my code.

推荐答案

如果希望通过代码更改属性时自动更新wpf表单，则需要 INotifyPropertyChanged .例如，有些控制器可能还想知道是否已进行了编辑以启用/禁用保存按钮.您可能还会在不同的视图上显示相同的属性.在这种情况下， INotifyPropertyChanged 可帮助您在编辑属性时立即更新另一个视图.

You need INotifyPropertyChanged if you want a wpf form to be automatically updated when a property changes through code. Also some controllers might want to know if edits have been made in order to enable/disable a save-button, for instance. You also might be displaying the same property on different views; in this case INotifyPropertyChanged helps to immediately update the other view when you edit a property.

如果您认为您的表单在没有 INotifyPropertyChanged 的情况下表现良好，则可以将其删除.

If you think that your form behaves well without INotifyPropertyChanged, then you can drop it.

请注意，即使没有 INotifyPropertyChanged ，绑定也可以工作.请参阅:为什么绑定更新没有实现INotifyPropertyChanged?

Note that binding works even without INotifyPropertyChanged. See: Why does the binding update without implementing INotifyPropertyChanged?

我将实现这样的属性.在极少数情况下，它可以帮助避免无休止的循环更新.顺便说一句，它更有效.

I would implement the properties like this. In some rare cases it can help to avoid endless circular updates. And it is more efficient by the way.

 private string _firstName;
 public string StudentFirstName
 {
     get { return _firstName; }
     set
     {
         if (value != _firstName) {
             _firstName = value;
             OnPropertyChanged("StudentFirstName");
         }
     }
 }

---

从C#6.0(VS 2015)开始，您可以像这样实现 OnPropertyChanged :

private void OnPropertyChanged(string propertyName)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

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