Question

I have a couple of textboxes binded with a Dictionary

<TextBox Text="{Binding Path=MyField[NotDefinedIndex], Mode=TwoWay}"></TextBox>

and it throws a “cannot connect to index” exception if I try to use a index not defined in the data context.
Is there a way to catch this error, define the index (MyFileld[“NotDefinedIndex”] = string.Empty) and then complete the binding?

Is there any way to bind on indexed properties in .NET Framework?

Answer 1

Hiding a binding error when you’re binding to an undefined index is probably not a very good idea; however, it’s possible to define a property that will access the dictionary and return string.Empty if the value doesn’t exist, so you won’t get a binding error. For example, in your view model:

public Dictionary<string, string> MyField { get; set; }

public string this[string key]
{
    get
    {
        string result;
        if (MyField.TryGetValue(key, out result))
        {
            return result;
        }

        return string.Empty;
    }
}

Then in XAML:

<TextBox Text="{Binding Path=[NotDefinedIndex], Mode=TwoWay}"></TextBox>