Question

I have a control with a property public MyClass MyProperty{...} which value is shown on the screen as a graph. I want this property to be bindable to any other MyClass in the program by using the Binding class (MyProperty would be the propertyName parameter in this Binding constructor, and the other MyClass would be the dataMember parameter) .

MyClass implements INotifyPropertyChanged so on that side everything is all right. But it happens that if I don’t implement a get accessor in MyProperty and try to bind something to it, I get a “Cannot bind to the property ‘MyProperty’ on the target control.
Parameter name: PropertyName” error.

Does this mean I have to implement a get accessor even if I know I will never need to read it’s value and I want a OneWay (source to target) binding, and even if I just return null in the get accessor?

I’m guessing the Binding class uses this to compare the new value to the old one or to do some other internal stuff. I’m not sure, then, if it’s a good idea to just return null, or it would be better to keep always a copy of whatever last object was assigned with the set accessor and return it in the get accessor. Maybe I really don’t even need to write a get accessor and I’m doing something else wrong. It just happens that I get the error only when I comment out the get accessor and stop getting it when I put it back.

Edit: In case there is any confusion: When I say MyProperty‘s value is shown on the screen as a graph I don’t mean it has a value that some other code reads and show in the screen. No one reads any value from MyProperty. MyProperty‘s set accessor is the one that draws stuff on the screen and that’s the end of the cycle.

Answer 1

I’m not 100% sure I understand what you mean, but I think the exception you’re encountering stems from the Binding class’s CheckBinding function (reflectored):

if (descriptor.IsReadOnly && (this.controlUpdateMode != ControlUpdateMode.Never))
{
    throw new ArgumentException(SR.GetString("ListBindingBindPropertyReadOnly", new object[] { this.propertyName }), "PropertyName");
}

Therefore, changing the Binding’s ControlUpdateMode to ControlUpdateMode.Never may be what you’re looking for