Cannot tab out of databound Winforms dropdown list

Question

This is a bit of a strange one, but I've been struggling for a few hours now and I can't understand what is happening.

I was wondering if anyone else has experienced this problem, and can perhaps explain it. I'm building a simple Winforms app and trying to use many of the built in controls.

Basically, I've got a form with a user control and some data capture fields. 3 of the fields are dropdown lists and on the user control I have a bindingSource control that binds directly to a Product class.

At run time I provide an instance of the Product class to the BindingSource and the class contains a property of ProductType. For simplicity I also added a List<ProductType> ProductTypes to the Product Class which loads itself when queried, which means I can just use the same bindingSource and choose the ProductTypes Data Member as the Datasource for the dropdownlist.

Upon running the form, the list binds perfectly and I can see all the product types listed, and I can select one and tab or click to the next field. But obviously the selected value won't bind because I've not chosen any bindings-SelectedValue for the dropdown, only a datasource. As soon as I make sure that the drop down modifies the instance of the Product by binding to the Bindings-SelectedValue, and then run the form, the list still gets populated perfectly and I can tab through the controls as long as I don't make a selection from the dropdown. If I make a selection from the dropdown then the dropdown holds focus. I cannot tab out for love or money and can't even click cancel button on the form, the close button top right is the only button I can click which works and I can't click any other field or dropdown. This affects all three dropdowns as soon as a selection is made.

Anyone have any ideas what I'm missing?

I have tried changing a few things and had some success by feeding the dropdown values a string[] instead of a member of an object. That seems to work, but defeats the object of using databinding doesn't it?

Any help appreciated!

Answer 1

Just guessing here, because I don't have time to set up a test and confirm right now, but are you doing any validating? I seem to remember that data-bound controls won't let you leave if the contents don't validate. Even if you aren't explicitly, try setting CausesValidation to False to see if there's any sort of validation going on behind the scenes, that might at least give you a hint.

Answer 2

Thanks for the input on this, helped me wrap my head around this.

In my case, it turns out that an exception was being thrown in one of the EventHadlers for my ComboBox.Validating event. It was hard to track down, because the IDE didn't show me that exception. I was able to modify the Exception behavior (in the debug menu) and have it show me any InvalidOperationException that was being thrown, and then I was able to track it down.

As Tom suggested, turning off CuasesValidation was the ticket to figuring it out.