To display the values, we were using all available records from a table specified as a the DataMember of the DataGridView object:
Instead of displaying all values, in some cases you may want to display only some values that respond to a criterion you set. Also, we were displaying the records in the order they appeared in the table. In some cases, you may want to re-arrange the order of records, following an arrangement of your choice. To perform these and other operations, you can create a data view. A data view is a control used to get a particular view of the records of a table. In order to use a data view, you must specify a table that the view gets its values from, and then use that data view to specify how the records should be displayed.
To support data views, the .NET Framework provides a class called DataView. Because a data view is a control, there are two ways you can create it: visually or programmatically. To visually create a data view, you must import it or add it to the Toolbox. To do this, you can right-click the Data section (actually you can right-click any section but the object would be added to the section you right-clicked; since the data view is a database object, it is a better idea to put it in the Data section) of the Toolbox and click Choose Items... In the .NET Framework Component property page, scroll down and put a check mark on DataView:
Click OK. This would add a DataView object to the Toolbox. From there, you can click the DataView button and click the form. To programmatically create a data view, declare a variable of type DataView and initialize it using one of its three constructors. The default constructor allows you to create a data view without specifying any detail. Here is an example: namespace Exercise5
{
public partial class Exercise : Form
{
DataView dvwStudents;
public Exercise()
{
InitializeComponent();
}
private void Exercise_Load(object sender, EventArgs e)
{
dvwStudents = new DataView();
}
}
}
In order to play its role, a data view must know the table on which it would apply its operations. Therefore, when creating a data view, the first piece of information you should provide is the table. Of course, you must have previously created a table, such as one from a data set. If you visually create a data view, to specify its table, in the Properties window, click the arrow of the Table field, expand the data set node and select the desired table:
To programmatically specify the table of a data view, you have various (three) options. If you had declared a DataView variable using the default constructor, to specify the table, you can assign the table by its index to the DataView.Table property. Here is an example: private void Exercise_Load(object sender, EventArgs e)
{
dvwStudents = new DataView();
dvwStudents.Table = dsStudents.Tables[0];
}
You can also use to object name of the variable. Here is an example: private void Exercise_Load(object sender, EventArgs e)
{
dvwStudents = new DataView();
dvwStudents.Table = dsStudents.Tables["Student"];
}
You can also use the variable table of the table. Here is an example: private void Exercise_Load(object sender, EventArgs e)
{
dvwStudents = new DataView();
dvwStudents.Table = tblStudent;
}
When declaring the DataView variable, to specify the table, the DataView class provides the following constructor: public DataView(DataTable table); This constructor expects a DataTable object as argument. Here are examples: public partial class Exercise : Form
{
DataView dvwStudents;
public Exercise()
{
InitializeComponent();
}
private void Exercise_Load(object sender, EventArgs e)
{
// Using the table's index in the data set
dvwStudents = new DataView(dsStudents.Tables[0]);
// Using the table object name
dvwStudents = new DataView(dsStudents.Tables["Student"]);
// Using the table variable name
dvwStudents = new DataView(tblStudent);
}
}
We already saw that, to create a data view, you could declare a variable of type DataView. You do not have to formally create a data view. To provide you with an alternative, the DataTable class is equipped with a property named DefaultView. This property produces a data view: public DataView DefaultView { get; }
This property allows you to access a default directly from a table object.
By default, when you display the records of a table in a control such as a data grid view, the records appear in the order they were created. Sorting records consists of arranging them in an alphabetical, numerical, or chronological order. To support this operation, you can use the DataView class. This class is equipped with a property of type string and named Sort. The DataView.Sort property expects the name of a column. The data view would arrange the records using that column as the basis. Here is an example:
private void rdoStudentNumber_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "StudentNumber";
}
private void rdoFirstName_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName";
}
private void rdoLastName_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "LastName";
}
private void rdoDateofBirth_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "DateOfBirth";
}
private void rdoGender_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "Gender";
}
When it comes to sorting, you can arrange a list in alphabetical or reverse alphabetical order, in numerical or reverse numerical order, in incremental or decremental order, in chronological or reverse chronological order. When sorting in alphabetical, numerical, incremental, in chronological order, you can specify the name of the column as done above or follow that name with the ASC operator. Here is an example: private void rdoStudentNumber_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "StudentNumber ASC";
}
To sort a list in reverse alphabetical, reverse numerical, decremental, or reverse chronological order, you must specify the name of the column followed by the DESC operator. Here is an example: private void rdoStudentNumber_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "StudentNumber DESC";
}
These operators are not case-sensitive. This means that ASC, Asc, and asc have the same effect. Here are examples:
private void rdoStudentNumberAsc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "StudentNumber asc";
}
private void rdoFirstNameAsc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName asc";
}
private void rdoLastNameAsc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "LastName asc";
}
private void rdoDateofBirthAsc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "DateOfBirth asc";
}
private void rdoGenderAsc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "Gender asc";
}
private void rdoStudentNumberDesc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "StudentNumber desc";
}
private void rdoFirstNameDesc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName desc";
}
private void rdoLastNameDesc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "LastName desc";
}
private void rdoDateofBirthDesc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "DateOfBirth desc";
}
private void rdoGenderDesc_CheckedChanged(object sender, EventArgs e)
{
dvwStudents.Sort = "Gender desc";
}
Here is an example of running the program:
So far, we specified that the sorting apply to only one column. You can ask the compiler (actually the interpreter) to sort more than one record. To do this, you would put the list of columns in a string, and then assign that string to the DataView.Sort property. Here is an example: private void btnSort_Click(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName, LastName";
}
When asked to arrange the records, the data view would sort the records based on the first column first, then the records would be arranged based on the second column. If you provide only the list of records, they would be arranged in ascending order. To enforce this, you can add the ASC operator on the right side of the list of columns. Here is an example: private void btnSort_Click(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName, LastName, DateOfBirth ASC";
}
To arrange the records in reverse order, add the DESC operator to the list of columns. Here is an example: private void btnSort_Click(object sender, EventArgs e)
{
dvwStudents.Sort = "FirstName, LastName DESC";
}
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