how-to-validate-input-with-the-windows-forms-datagrid-control.md

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Validate Input with DataGrid Control	Learn how to validate input with the Windows Forms DataGrid control, which is retained for both backward compatibility and future use.	03/30/2017	csharp vb	DataGrid control [Windows Forms], examples user input [Windows Forms], validating examples [Windows Forms], DataGrid control DataGrid control [Windows Forms], validating input validation [Windows Forms], user input	f1e9c3a0-d0a1-4893-a615-b4b0db046c63

How to: Validate Input with the Windows Forms DataGrid Control

Note

The xref:System.Windows.Forms.DataGridView control replaces and adds functionality to the xref:System.Windows.Forms.DataGrid control; however, the xref:System.Windows.Forms.DataGrid control is retained for both backward compatibility and future use, if you choose. For more information, see Differences Between the Windows Forms DataGridView and DataGrid Controls.

There are two types of input validation available for the Windows Forms xref:System.Windows.Forms.DataGrid control. If the user attempts to enter a value that is of an unacceptable data type for the cell, for example a string into an integer, the new invalid value is replaced with the old value. This kind of input validation is done automatically and cannot be customized.

The other type of input validation can be used to reject any unacceptable data, for example a 0 value in a field that must be greater than or equal to 1, or an inappropriate string. This is done in the dataset by writing an event handler for the xref:System.Data.DataTable.ColumnChanging or xref:System.Data.DataTable.RowChanging event. The example below uses the xref:System.Data.DataTable.ColumnChanging event because the unacceptable value is disallowed for the "Product" column in particular. You might use the xref:System.Data.DataTable.RowChanging event for checking that the value of an "End Date" column is later than the "Start Date" column in the same row.

To validate user input

1. Write code to handle the xref:System.Data.DataTable.ColumnChanging event for the appropriate table. When inappropriate input is detected, call the xref:System.Data.DataRow.SetColumnError%2A method of the xref:System.Data.DataRow object.

   Private Sub Customers_ColumnChanging(ByVal sender As Object, _
   ByVal e As System.Data.DataColumnChangeEventArgs)
      ' Only check for errors in the Product column
      If (e.Column.ColumnName.Equals("Product")) Then
         ' Do not allow "Automobile" as a product.
         If CType(e.ProposedValue, String) = "Automobile" Then
            Dim badValue As Object = e.ProposedValue
            e.ProposedValue = "Bad Data"
            e.Row.RowError = "The Product column contains an error"
            e.Row.SetColumnError(e.Column, "Product cannot be " & _
            CType(badValue, String))
         End If
      End If
   End Sub

   //Handle column changing events on the Customers table
   private void Customers_ColumnChanging(object sender, System.Data.DataColumnChangeEventArgs e) {
   
      //Only check for errors in the Product column
      if (e.Column.ColumnName.Equals("Product")) {
   
         //Do not allow "Automobile" as a product
         if (e.ProposedValue.Equals("Automobile")) {
            object badValue = e.ProposedValue;
            e.ProposedValue = "Bad Data";
            e.Row.RowError = "The Product column contains an error";
            e.Row.SetColumnError(e.Column, "Product cannot be " + badValue);
         }
      }
   }

2. Connect the event handler to the event.

   Place the following code within either the form's xref:System.Windows.Forms.Form.Load event or its constructor.

   ' Assumes the grid is bound to a dataset called customersDataSet1
   ' with a table called Customers.
   ' Put this code in the form's Load event or its constructor.
   AddHandler customersDataSet1.Tables("Customers").ColumnChanging, AddressOf Customers_ColumnChanging

   // Assumes the grid is bound to a dataset called customersDataSet1
   // with a table called Customers.
   // Put this code in the form's Load event or its constructor.
   customersDataSet1.Tables["Customers"].ColumnChanging += new DataColumnChangeEventHandler(this.Customers_ColumnChanging);

See also

• xref:System.Windows.Forms.DataGrid
• xref:System.Data.DataTable.ColumnChanging
• xref:System.Data.DataRow.SetColumnError%2A
• DataGrid Control