Tài liệu Using the Data Form Wizard to Create a Windows Form phần 2 doc

Figure 6.23: Creating a relationship between two tables Note Remember: You're unselecting these columns, so you uncheck the columns for the Orders table. Figure 6.24 shows the completed dialog box with the selected columns to display from each table. Figure 6.24: Selecting the columns to display from each table 8. Click the Next button to proceed. 9. Select the display style for the rows (also known as records) in the parent table that are displayed in your form. You can display the rows in a grid, or you can display each column using a separate control. You'll use a separate control for the columns, so select the Single Record in individual controls radio button. The other check boxes in the dialog box allow you pick the controls you want to add to your form. These controls affect the rows in the master table, and you can add the following controls to your form: Note In this example, the parent table is the Customers table, and the child table is the Orders table. The rows for the child table are displayed in a DataGrid control. o Cancel All The Cancel All button allows you to undo any changes you've made to the current row. o Add The Add button allows you to add a new row. o Delete The Delete button allows you to delete the current row. o Cancel The Cancel button allows you to cancel a change made to the current row. o Navigation Controls The Navigation controls consist of four buttons that allow you to move to first row, the previous row, the next row, and the last row. An indicator is also displayed to show the current row. Figure 6.25 shows the completed dialog box. Figure 6.25: Choosing the display style 10. You've now completed all the steps in the Data Form Wizard. Click the Finish button to create your form. VS .NET will now display the new form, as shown in Figure 6.26 . Figure 6.26: The completed form The managed provider objects in your form use the OLE DB classes contained in the System.Data.OleDb namespace-even though a SQL Server database is used. These objects work with any OLE DB-compliant database. The code would be more efficient if the managed provider classes in the System.Data.SqlClient namespace were used instead; these classes are specifically for use with a SQL Server database. This is the price of having the VS .NET wizard generate the code for you. In the next section , you'll learn how the text-box controls in your form access the columns in the Customers table. Data Binding Each text-box control in the upper part of your form is bound to a column in the Customers table using a process known as data binding. When a control is bound to a column in a DataSet object, the value for that column is displayed in the control through the Text property in the DataBindings group. The Text property in the DataBindings group sets the text displayed in a control. To examine or set the data binding for a control, you select the control in the form designer and expand the DataBindings properties in the Properties window. You'll see these properties in the Data area of the Properties window. Next, you'll see how the text box for the Customer ID is set. Select the text box to the right of the CustomerID label in your form; this text box is named editCustomerID. Make sure the DataBindings properties are expanded in the Properties window. Finally, click the drop-down list for the Text property to view the current column to which the text box is bound. As you can see from Figure 6.27 , editCustomerID is bound to the CustomerID column of the Customers table. This means that when you run the form and load data from the database, the CustomerID column value will be displayed in the editCustomerID text box. Figure 6.27: The editCustomerID text box is bound to the CustomerID column In the next section , you'll add a label and a text-box control to display the City column in your form. Adding Controls to the Form When you ran the Data Form Wizard earlier to create your form, you'll recall that I told you to unselect the City column of the Customers table so that it didn't appear on your form. I asked you to do this so that you can now see how to manually add a control and bind it to the City column. That way, you can see how to build your own forms that access the database. Follow these steps to add a label and a text box to your form: 1. Add a label below the Address label in your form. Set the Name property for your new label to lblCity. 2. Set the Text property for your label to City. 3. Next, add a text box below the editAddress text box. 4. Set the Name property for your new text box to editCity. 5. Remove the current text from the Text property so that no default text is shown in the control. Next, you need to bind editCity to the City column of the Customers table. To do this, you open the DataBindings properties and set the text property by selecting City from the Customers table, as shown in Figure 6.28 . Figure 6.28: Binding the City column to the editCity text box In the next section , you'll add a Main() method to the code of your form. Adding the Main() Method As you know, all programs must have a Main() method. The Main() method is executed when you run your program. In this section, you'll add a Main() method to your form. To do this, select View ➣ Code, and add the following Main() method inside your MyDataForm class (a good place to add Main() would be at the start of your MyDataForm class after the open curled bracket {): public class MyDataForm : System.Windows.Forms.Form { public static void Main() { Application.Run(new MyDataForm()); } . This code creates a new object of the MyDataForm class, causing your form to be displayed on the screen. Setting the Password Before you can run your form, you need to set the password for the database user in the ConnectionString property of the data connection object. This object was automatically created by VS .NET when you ran the Data Form Wizard, and the object has the default name oleDbConnection1. To modify the ConnectionString property for oleDbConnection1, select oleDbConnection1 from the drop-down list in the Properties window. Go ahead and add the text pwd=sa in the ConnectionString property, as shown in Figure 6.29 . Figure 6.29: Setting the ConnectionString property You're now ready to run your form. Running the Form To run your form, select Debug ➣ Start without Debugging. Figure 6.30 shows the running form. You click the Load button to display the rows from the Customers and Orders tables in your form. Figure 6.30: The running form Note You'll see a Windows console appear in the background. Don't worry about it. Notice that the top part of the form shows the details for the row from the Customers table where the CustomerID is ALFKI; the bottom part of the form contains a DataGrid control that displays the rows from the Orders table for that customer. When you move to the next row in the Customers table, the rows from the Orders table for that customer are automatically displayed in the DataGrid. Feel free to try out the other buttons on your form to add, modify, and delete rows in the Customers table. You can also use the DataGrid control to add, modify, and delete rows from the Orders table for the current customer. . of the data connection object. This object was automatically created by VS .NET when you ran the Data Form Wizard, and the object has the default name. MyDataForm class (a good place to add Main() would be at the start of your MyDataForm class after the open curled bracket {): public class MyDataForm :