How to bind one texblock value to other textblock one way and get value in MVVM

问题

Let me explain my question by an Image

I have MVVM structure in My project. I have two textblocks, Textblock 1 and textblock 2. Now I want textblock2's Text same as Textblock1's Text, whenever Textblock1's Text changed. but I should be able to set Textblock2's Text different from Textblock1's. So I am setting Oneway binding of Textblock1's Text Property.

How Can I get the Text property of Textblock2's In MVVM. If I create a property for Textblock2's Text property, I wont be able to bind Textblock1's text to textblock2.

Let me know if I want to clear my question further.

Thanks in anticipation.

回答1:

Use two properties in VM, and implement the equal/override logic there. That's exactly the kind of stuff VMs are good in.

VM 
  Prop1 <-- Binding- TextBlock1
  Prop2 <-- Binding- TextBlock2

The Prop1 setter is implemented such that it also updates Prop2 (don't forget INotifyPropertyChanged), if you set Prop2 make it to switch to and keep the different value.

回答2:

Here is the code to go along with flq's answer:

public class MyViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string _text1;
    private string _text2;

    public string Text1
    {
        get { return _text1; }
        set
        {
            if (_text1 != value)
            {
                _text1 = value;                    

                RaisePropertyChanged("Text1");

                Text2 = _text1;
            }
        }
    }        

    public string Text2
    {
        get { return _text2; }
        set
        {
            if (_text2 != value)
            {
                _text2 = value;

                RaisePropertyChanged("Text2");
            }
        }
    }

    public MyViewModel()
    {

    }

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

Be sure to change your bindings to two-way.

EDIT:

Here is the XAML:

<TextBox Text="{Binding Text1, UpdateSourceTrigger=PropertyChanged}" />
<TextBox Text="{Binding Text2}" />

Setting UpdateSourceTrigger=PropertyChanged allows the property to be updated as you type, so TextBox2 will update as you type. (FYI - The default bindings for TextBoxes is Two-Way)

来源：https://stackoverflow.com/questions/14766798/how-to-bind-one-texblock-value-to-other-textblock-one-way-and-get-value-in-mvvm