【正文】 10 Support for custom validation events Checking for required values in input Displaying error icons next to controls Showing message summary with links to controls Adding binding errors programmatically To use the control, you simply drop it into an page. The control acts as an extender control for any existing controls on the form, and it adds a DataBindingItem property to the extended control in the Visual Studio174。t rendered at run time. It39。s possible to bind , where this refers to the Page object (which is the base object from which any binding expression originates). Binding is performed using a BindingSource to identify a data item. The BindingSource consists of two propertiesBindingSource (which is a string property that describes the base object) and BindingSourceMember (which provides the mapping of the field or property to bind to). Programmatic access can also make use of the BindingSourceObject property to provide a reference instead of a BindingSource string. Suppose you want to bind to a DataRow object. In order for wwDataBinder to bind to the DataRow, the DataRow needs to be accessible through a Page reference. So works. In this case, you39。d bind with: BindingSource: BindingSourceMember: CompanyName You can bind to a DataTable in the same way. When a DataTable or DataSet is used as the BindingSource object, wwDataBinder assumes the first DataRow for a table or the first table and first DataRow for a DataSet. You can also bind an object more directly, like so: BindingSource: [Products].Rows[0] BindingSourceMember: CompanyName Just remember that in order for the wwDataBinder to be able to bind, whatever object you39。t need to be specified. A BindingSource is relative to a toplevel container objecttypically the Page objectbut you can supply the toplevel container as part of the DataBind and Unbind methods as a parameter. This is useful if you want to use the wwDataBinder in a user control where the toplevel container is the UserControl rather than the page. BindingSourceMembers are always simple types like ints, strings, DateTime, bool, and so on. They can also be Enum values, which are translated into strings and work for twoway binding. The job of a BindingSource is to establish a binding between a data item or property and the control property to which the value is bound. This mapping is used both for binding to a control property and from a control property back into the data item or property. Inbound binding is established by calling the method, and unbinding is done by calling . The process is deterministic in that you explicitly call these methods from your codethis provides a lot of flexibility in terms of how binding is handled. A DataBindingItem exposes additional properties that are associated with the data binding process, as shown in Figure 1. The BindingProperty determines the field of the control you are binding tothe default is Text, but if you39。re binding to a list control to SelectedValue. Data binding can be oneway, twoway, or none. Input controls like textboxes generally use twoway binding, while display controls like labels use oneway binding. None is useful if you want a control to participate in binding error management, but you don39。s BindingErrorMessage programmatically and return false to let the binder know that this DataBindingItem is in error and needs to display on the error list. The last error is a purely programmatic error that is added by using and specifying the error message and Control instance or ID in the Page code. This allows assigning an arbitrary error message to a control that is data bound and makes the control show up both with the icon and in the error listing. All of this provides for automatic and fully programmatic binding error generation so there39。s string output to the text property. The control also has easy message display methods, like ShowError and ShowMessage, which display oneline messages with an icon, providing a consistent way to display messages on a Page. You