A User Interface Component by Net Solutions srl

Web Combobox is an ASP.NET web custom control to be used in substitution of the less advanced standard DropDownList. It includes a wide range of features, among which load on demand, multiple columns, predefined layouts, that make it irreplaceable with traditional native controls.

The possibility to load on demand the list of the displayed items makes it particularly useful in every case where the dimension of the data sources is equal to hundreds or thousands records, when the download in a unique solution would cause unacceptable waiting times, especially in presence of slow links.

The use of the mousewheel, the winning design and the high performances make it a highly professional product able to guarantee a user's experience of remarkable impact.

Features:

Load on demand
The control is able to retrieve the data from the server only when demanded for the display, carrying out the download with a modality that does not cause postback, in a transparent way to the user. Such functionality, even if based on a simple paging activity, produces a significant increasing of the perceived performances and virtualizes the presence on the client of the data not yet really downloaded.

Extensible predefined layouts
The control has a set of predefined layouts that make extremely simple to set up the look & feel in execution phase. Such set can be easily extended modifying the layout definition file, formed of a css style sheet containing one or more classes for every graphic element. The layout list so defined is displayable and immediately usable at design time for assignation of the BaseCssLayout property.

Multiple columns
Unlike the standard DropDownList, our control permits the display of the contents on one or more columns.
For every column it is possible to define the header title, the css styles to be applied and the data source for the binding, being able to choose the content type between only text, only image or text plus image.
In the event handler BindRowEvent it is furthmore possible specify programmatically the content to be displayed in every column.

Data binding
Extreme granularity in the style settings
The control is formed of ten distinct graphic elements (three of them permit a double definition of the style characteristics - onmouseover and onmouseout) and the style of every element is definable setting up, at design time or at runtime, the numerous properties such as BackColor, ForeColor, Font and so on. Every column has its own indipendent style.
It is provided the possibility to assign two values related to the background color, BackColor and BackColorGradient, that will be used respectively as start color and end color for a pleasent blur effect.

Full support of the postback pattern
Deactivated for default, the postback is controlled by the value of the property AutoPostBack. When this property is true, the selection of an item from the list causes an automatic call to the server side event SelectedItemChanged. The server side event ServiceButtonOnClick is instead generated, performing a postback, when one of the eventually defined service buttons is clicked.
The value persistence of all control properties is guaranteed during the postback by a complete management of the viewstate (this functionality is deactive for default and activable through the property EnableViewState).

Client side events
Support of the mousewheel and of the direction keys
To browse the list it can be used either the direction keys (Up,Down, PageUp, PageDown) or the mousewheel. The item selection occurs either with Enter key or with a click. Trying to continue with the browsing further the last displayed element, it is obtained the automatic load of the next page (the size of the page is fixed by the PageSize property).

Perfect integration in Microsoft Visual Studio.NET
Complete control of drop down behaviour
The data retrieving and the consequent display of selected items occurs spontaneously in consequence of the typing of the search key in the proper textbox element. Yet it is possible customize the behaviour of the control with the properties Latency and MinCharsToRequest, in order to avoid useless and expensive round trips. Thanks to this properties it is possible to define, respectively, either the minimum time of inactivity of the keyboard or the minimum number of characters in the textbox to be used as thresholds values to activate the request to the server.

User defined service buttons
It is possible to define an array of service buttons, perfectly integrated from the graphic point of view, usable to obtain functionalities absent in the control (contextual help, append of new items, and so on).
The click on the buttons is handled through the server side event ServiceButtonOnClick.