分配不同类型的对象

Question

I am new to VB.Net and I'm a little confused why this line happened to be valid in VB:

DataGridView1.DataSource = ds.Tables("Customerslist")

DataSource is of type Object while Tables("Customerslist") is of type DataTable. How will I know what types of objects can be assigned to the Datasource property?

Answer 1

DataTable derives from Object , so can be assigned to any Object variable.

From MSDN ( DataSource ):

The DataGridView class supports the standard Windows Forms data-binding model. This means the data source can be of any type that implements one of the following interfaces:

• The IList interface, including one-dimensional arrays.
• The IListSource interface, such as the DataTable and DataSet classes.
• The IBindingList interface, such as the BindingList class.
• The IBindingListView interface, such as the BindingSource class.

Answer 2

In .NET all classes are ultimately derived from object so field/property of type object can be used to store a reference to anything.

This can be useful when you need to store a reference to something that might be one of a number of potentially related types. It does mean though that when you come to use that reference you need to check what type it really is.