Get source property type from BindingExpression

问题:

I am trying to find out the source property type of a binding expression. I want to do this because I want to use the UpdateSourceExceptionFilter to provide a more useful error message than just the generic “couldn’t convert”.

In .NET 4.5 I use ResolvedSource and ResolvedSourcePropertyName with reflection to get the source property type like this:

PropertyInfo sourceProperty = expr.ResolvedSource.GetType().GetProperty(expr.ResolvedSourcePropertyName);
Type propertyType = sourceProperty.PropertyType;

This works just fine. However both those BindingExpression properties were just introduced with .NET 4.5, and I’m still on 4.0 (can’t really update because of Windows XP).

So is there a nice way to do this in .NET 4.0? I thought about getting the internal SourceItem and SourcePropertyName properties using reflection or just the private Worker to get those values but I would rather avoid to access internal/private properties or fields (and I think this would also require me to do something about trust? What implications are there?).

回答1:

Not too pretty, but without access to private methods:

string[] splits = expr.ParentBinding.Path.Path.Split('.');
Type type = expr.DataItem.GetType();
foreach (string split in splits) {
    type = type.GetProperty(split).PropertyType;
}

Thus, we are able to resolve the source property.

回答2:

Here is one solution that is independent from internal/private .NET objects.

Property expr.ResolvedSource is null when DataContext is used from parent control, so it will not be useful.

What is the reason to finding source type?

Why do not use simple String.Format("Binding has exception in path {0}", expr.ParentBinding.Path.Path?? String.Empty)?

回答3:

i use this in my code to find source property Type

        BindingExpression bindingExpression = BindingOperations.GetBindingExpression(this, SelectedItemProperty);
        object s = bindingExpression?.ResolvedSource;
        string pn = bindingExpression?.ResolvedSourcePropertyName;

        var type = s?.GetType().GetProperty(pn)?.PropertyType;