Editing a textbox using multi binding

Question

I have a textbox using multi binding. The fields used for this multi binding are properties coming from my data view model

<TextBox>
    <TextBox.Text>
        <MultiBinding StringFormat="{}{0} {1}">
            <Binding Path="FirstProperty" />
            <Binding Path="SecondProperty" />
        </MultiBinding>
    </TextBox.Text>
</TextBox>

I would like to keep this behavior while allowing the user to update the content; I would then retrieve the content of the textbox in my data view model.

Is it possible?

Answer 1

While the link that pangabiMC points to uses a converter I personally wouldn't myself, it's easier to both debug and unit test if you put this behaviour in the view model. Just create a separate property for your textbox (CombinedProperty) and keep it synced to the original properties:

public class YourViewModel : ViewModelBase
{
    private string _FirstProperty = "";
    public string FirstProperty
    {
        get { return this._FirstProperty; }
        set
        {
            this._FirstProperty = value;
            RaisePropertyChanged(() => this.FirstProperty);
            UpdateCombinedProperty();
        }
    }

    private string _SecondProperty = "";
    public string SecondProperty
    {
        get { return this._SecondProperty; }
        set
        {
            this._SecondProperty = value;
            RaisePropertyChanged(() => this.SecondProperty);
            UpdateCombinedProperty();
        }
    }

    private string _CombinedProperty = "";
    public string CombinedProperty
    {
        get { return this._CombinedProperty; }
        set
        {
            this._CombinedProperty = value;
            RaisePropertyChanged(() => this.CombinedProperty);
            UpdateSourceProperties();
        }
    }

    private void UpdateCombinedProperty()
    {
        this.CombinedProperty = this.FirstProperty + " " + this.SecondProperty;
    }

    private void UpdateSourceProperties()
    {
        var fields = this.CombinedProperty.Split(' ');
        if (fields.Length != 2)
            return; // should handle validation properly
        this.FirstProperty = fields[0];
        this.SecondProperty = fields[1];
    }

}