Tài liệu Using a DataView to Control Edits, Deletions, or Additions in Windows Forms pdf

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Recipe 7.14 Using a DataView to Control Edits, Deletions, or Additions in Windows
Forms
Problem
You need to selectively prevent users from editing, deleting, or adding data in a Windows
Forms application.
Solution
Bind a DataView to Windows Forms controls.
The sample code contains four event handlers:
Form.Load
Sets up the sample by filling a DataTable with the Orders table from the
Northwind sample database. A DataView is created from the table and bound to
the data grid on the form.
Allow Delete Button.Click
Sets whether the DataView allows records to be deleted based on the value in a
check box.
Allow Edit Button.Click
Sets whether the DataView allows records to be edited based on the value in a
check box.
Allow Insert Button.Click
Sets whether the DataView allows records to be inserted based on the value in a
check box.
The C# code is shown in Example 7-30
.
Example 7-30. File: ControlDataEditWithDataViewForm.cs
// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Data;

using System.Data.SqlClient;

private DataView dv;

// . . .

private void ControlDataEditWithDataViewForm_Load(object sender,
System.EventArgs e)
{
// Fill the Order table.
SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Orders",
ConfigurationSettings.AppSettings["Sql_ConnectString"]);
DataTable dtOrders = new DataTable("Orders");
da.FillSchema(dtOrders, SchemaType.Source);
da.Fill(dtOrders);

// Create a view and bind it to the grid.
dv = new DataView(dtOrders);
dataGrid.DataSource = dv;
}

private void allowDeleteCheckBox_CheckedChanged(object sender,
System.EventArgs e)
{
dv.AllowDelete = allowDeleteCheckBox.Checked;
}

private void allowEditCheckBox_CheckedChanged(object sender,
System.EventArgs e)
{

dv.AllowEdit = allowEditCheckBox.Checked;
}

private void allowInsertCheckBox_CheckedChanged(object sender,
System.EventArgs e)
{
dv.AllowNew = allowInsertCheckBox.Checked;
}
Discussion
The DataGrid control does not have properties that control the adding, editing, or deleting
the data in the control. Binding a DataGrid to a DataTable binds to the default view of the
underlying DataTable.
The DataView class represents a view of the DataTable that can be data bound on both
Windows Forms and Web Forms. The DataView can be customized for editing, filtering,
searching, and sorting.
The DataView class can be used to add, edit, or delete records in the underlying
DataTable. The properties described in Table 7-14
control the data modification
permitted in a DataView.
Table 7-14. DataView properties
Property Description
AllowDelete Gets or sets a Boolean value indicating whether deletes are allowed
AllowEdit Gets or sets a Boolean value indicating whether edits are allowed
AllowNew Gets or sets a Boolean value indicating whether new rows can be added
If AllowNew is true, the record is not added until the EndEdit( ) method is called either
explicitly or implicitly. The CancelEdit( ) method of the DataRowView can be called to
discard the row before it is added.
If AllowEdit is true, the changes to the row are not committed until the EndEdit( )
method is called either explicitly or implicitly. Only one row can be edited at a time. The
CancelEdit( ) method of the DataRowView can be called to discard the row before it is

added.
If the AddNew( ) or BeginEdit( ) method of the DataRowView is called, EndEdit( ) is
called implicitly on the pending row; this applies the changes to the row in the underlying
DataTable. In data controls that allow editing multiple records, EndEdit( ) is called
implicitly when the current row is changed.

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