对象属性的 xamarin.form 双向绑定不起作用

Question

myview
<Image Grid.Column="0" Grid.Row="0" Source="contactIcon.png" />
<Entry Grid.Column="1" Grid.Row="0"  Text="{Binding 
SelectedContact.FNAME,Mode=TwoWay}" Placeholder="First Name" />
<Entry Grid.Column="1" Grid.Row="1"  Text="{Binding 
SelectedContact.LNAME,Mode=TwoWay}" Placeholder="Last Name"/>
<Image Grid.Column="0" Grid.Row="2" Source="calIcon.png" />
<Entry Grid.Column="1" Grid.Row="2" Text="{Binding 
SelectedContact.PHONE,Mode=TwoWay}" Placeholder="Mobile" 
Keyboard="Telephone"/>
<Image Grid.Column="0" Grid.Row="3" Source="emailIcon.png" />
<Entry Grid.Column="1" Grid.Row="3" Text="{Binding 
SelectedContact.EMAIL,Mode=TwoWay}" Placeholder="Email" Keyboard="Email"/>
<Entry Grid.Column="1" Grid.Row="4" Text="{Binding 
SelectedContact.BALANCE,Mode=TwoWay}" Placeholder="Email" 
Keyboard="Email"/>

Contact model
    public int ID { get; set; }
    public string FNAME { get; set; }
    public string LNAME { get; set; }
    public string PHONE { get; set; }
    public string EMAIL { get; set; }
    public Double BALANCE { get; set; }

ContactViewModel
private Contact _selectedContact;
public Contact SelectedContact{get { return _selectedContact; }set{ 
_selectedContact = value; OnPropertyChanged(); } }

单向绑定正在工作，但我想要双向绑定。如果我更改文本或修改名字条目中的文本，那么它应该更改 SelectedContact 的 FNAME 属性

Answer 1

    protected void RaisePropertyChanged(String property)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }

    protected void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpression)
    {
        MemberExpression expression = propertyExpression.Body as MemberExpression;
        RaisePropertyChanged(expression.Member.Name);
    }


    public event PropertyChangedEventHandler PropertyChanged;

在您的视图中尝试此操作以更改属性

RaisePropertyChanged(()=>YourPropertyName);

Answer 2

您必须实现 INotifyPropertyChanged，它是双向绑定的主接口。在您的视图模型类中，您必须以这种方式实现

 public class ContactViewModel: INotifyPropertyChanged 
 { 
   private Contact _selectedContact;
   public Contact SelectedContact
   { 
      get 
       { return _selectedContact; }
      set
       { _selectedContact = value;
        OnPropertyChanged(); 
       } 
    }
  public event PropertyChangedEventHandler PropertyChanged;  
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) {  
        PropertyChanged ? .Invoke(this, new PropertyChangedEventArgs(propertyName));  
    }
} 

在你的 MainPage()

public MainPage() {  
        InitializeComponent();  
        vm = new ContactViewModel();  
        BindingContext = vm;  
    }