Introducción En algunas situaciones se requiere agregar un ítem especial a los controles, como ser en controles del tipo combo, para que el usuario tenga la posibilidad de indicar que no hay un ítem escogido de la lista.

Esto se usa especialmente en circunstancias en donde el campo que representa el combo es opcional, o se quiere inicializar en un ítem que obligue al usuario a elegir un valor de la lista.

vb net validating combobox-19

So, your next step is to add a Setting, of the type of your custom class, to your application: Right-click your Project name at the top of Solution Explorer, then select Properties from the pop-up menu. I’m going to assume a situation like mine, where you want to bind a settings object to an options dialog window.

This opens the Properties editor; click “Settings” on the left side. There is, however, a workaround…or I wouldn’t have bothered writing this article! I came across many blog articles and forum posts discussing the best approach. OK, now it’s time for a little databinding, then a little code. Go to the Data Sources tab, which should be in the same window as the Solution Explorer, and click on “Add New Data Source…”.

Según cual sea el origen de datos cambia la solución que debe aplicarse para agregar este ítem extra opcional de la lista, ya que será el origen de datos donde se agrega la opción especial.

Agregar opción usando clases creadas por uno En el ejemplo se ha definido una clase de nombre “Producto”, es muy simple, solo cumple la función de definir la información que necesitas el control.

A design surface and hundreds of controls and components let you rapidly build sophisticated, powerful UI-driven sites with data access.

Visual Studio Express provides a free development tool that makes ASP.

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Unless you are using a grid control or something similar that will contain all the properties in one control, you will want to change the top-most item, representing your entire class, from “None” (the well-known circle with a slash icon) to “Details”.

Then, when you have everything the way you want, simply drag that top-most item and drop it right on your form; the controls you chose will then be added to the form, all ready to be data-bound, and a Binding Source control will appear at the bottom of your dialog form, generally named after your object: Settings Class Binding Source.

And there is no clean, easy way to validate the data.