Use the Binding class to create and maintain a simple binding between the property of a control and either the property of an object, or the property of the current object in a list of objects.
As an example of the first case, you can bind the Text property of a TextBox control to the FirstName property of a Customer object. As an example of the second case, you can bind the Text property of a TextBox control to the FirstName property of a DataTable that contains customers.
The Binding class also enables you to format values for display through the Format event and to retrieve formatted values through the Parse event.
When constructing a Binding instance with Binding constructor, you must specify three items:
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The name of the control property to bind to.
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The data source.
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The navigation path that resolves to a list or property in the data source. The navigation path is also used to create the object's BindingMemberInfo property.
First, you must specify name of the control property you want to bind the data to. For example, to display data in a TextBox control, specify the Text property.
Second, you can specify an instance of any of classes in the following table as the data source.
| Description | C# example |
| Any class that implements IBindingList or ITypedList. These include: DataSet, DataTable, DataView, or DataViewManager. | | DataSet ds = new DataSet("myDataSet"); |
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| Any class that implements IList to create an indexed collection of objects. The collection must be created and filled before creating the Binding. The objects in the list must all be of the same type; otherwise, an exception will be thrown. | | ArrayList ar1 = new ArrayList;
Customer1 cust1 = new Customer("Louis");
ar1.Add(cust1); |
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| A strongly typed IList of strongly typed objects | | Customer [] custList = new Customer[3]; |
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Third, you must specify the navigation path, which can be an empty string (""), a single property name, or a period-delimited hierarchy of names. If you set the navigation path to an empty string, the ToString method will be called on the underlying data source object.
If the data source is a DataTable, which can contain multiple DataColumn objects, the navigation path must be used to resolve to a specific column.
Note |
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| When the data source is a DataSet, DataViewManager, or DataTable, you are actually binding to a DataView. Consequently, the bound rows are actually DataRowView objects. |
A period-delimited navigation path is required when the data source is set to an object that contains multiple DataTable objects (such as a DataSet or DataViewManager). You can also use a period-delimited navigation path when you bind to an object whose properties return references to other objects (such as a class with properties that return other class objects). For example, the following navigation paths all describe valid data fields:
Each member of the path can return either a property that resolves to a single value (such as an integer), or a list of values (such as an array of strings). Although each member in the path can be a list or property, the final member must resolve to a property. Each member builds on the previous member: "Size.Height" resolves to the Height property for the current Size; "Regions.regionsToCustomers.CustomerFirstName" resolves to the first name for the current customer, where the customer is one of the customers for the current region.
A DataRelation returns a list of values by linking one DataTable to a second DataTable in a DataSet. If the DataSet contains DataRelation objects, you can specify the data member as a TableName followed by a RelationName, and then a ColumnName. For example, if the DataTable named "Suppliers" contains a DataRelation named "suppliers2products", the data member could be "Suppliers.suppliers2products.ProductName".
The data source can consist of a set of related classes. For example, imagine a set of classes that catalogs solar systems. The class named System contains a property named Stars that returns a collection of Star objects. Each Star object has Name and Mass properties, as well as a Planets property that returns a collection of Planet objects. In this system, each planet also has Mass and Name properties. Each Planet object further has a Moons property that returns a collection of Moon objects, each of which also has Name and Mass properties. If you specify a System object as the data source, you can specify any of the following as the data member:
Controls that can be simple-bound feature a collection of Binding objects in a ControlBindingsCollection, which you can access through the control's DataBindings property. You add a Binding to the collection by calling the Add method, thereby binding a property of the control to a property of an object (or to a property of the current object in a list).
You can simple-bind to any object that derives from the System.Windows.Forms.Control class, for example, the following Windows controls:
Note |
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| Only the SelectedValue property of the ComboBox, CheckedListBox, and ListBox control is simple bound. |
The BindingManagerBase class is an abstract class that manages all the Binding objects for a particular data source and data member. Classes that derive from BindingManagerBase are the CurrencyManager and the PropertyManager classes. How a Binding is managed depends on whether the Binding is a list binding or a property binding. For example, if it is a list binding, you can use the BindingManagerBase to specify a Position in the list; the Position, therefore, determines which item (out of all items in the list) is actually bound to a control. To return the appropriate BindingManagerBase, use the BindingContext.
To add a new row to a set of controls bound to the same DataSource, use the AddNew method of the BindingManagerBase class. Use the Item property of the BindingContext class to return the appropriate CurrencyManager. To escape the addition of the new row, use the CancelCurrentEdit method.