Tài liệu Put the Finishing touches On A Data Bound Form pdf

1.7 Put the Finishing Touches on a Data Bound Form Besides handling the basics, you need to add some finishing touches to a data entry form, such as enabling/disabling controls based on whether you're on a record. This How-To shows you how to use the Enabled properties on controls to give the user more direction when using a Windows form (see Figure 1.12). Figure 1.12. You will create this complete form by How-To 1.7, with all the bells and whistles that users expect from a good data entry form. Although the majority of the major issues are taken care of for the form you created so far in the chapter, your users become confused about when to push some of the buttons. How do you get the buttons to reflect when the users can click them, and what other finishing touches might help the form? Technique An important part of user interfaces is letting the user know when he has access to certain features on the form. In this case, you will see how to do the following: • Toggle the enabled property of the btnSave, btnCancel, btnNew, and btnDelete at the appropriate moments, such as when a record is highlighted in the list box. • Add a command button to close the form. • Add code to the Closing event of the form that tests whether you have made changes to the current record, and if so, whether you want to save the changes. You can see an example of particular command buttons being enabled based on the current action being performed in the form in Figure 1.13. Figure 1.13. This form allows users to access command buttons only when the functionality is available. Steps Continuing on with the form that you have been using, you are going to make the changes just mentioned in the previous bulleted list. 1. Start by modifying two routines already created: RefreshIndividual and ActivateEditing subroutines. Then check whether a customer has been selected in lstCustomers. If not, then the two buttons, btnEdit and btnDelete, are disabled. If a customer hasn't been selected, the two buttons are enabled, and the dsCustomerIndividual dataset control is refreshed. Listing 1.19 frmHowTo1_7.vb: Toggling the Enabled Property of the btnEdit and btnDelete Buttons Private Sub RefreshIndividual() '- Clear individual customer dataset Me.dsCustomerIndividual.Clear() If lstCustomers.SelectedIndex = -1 Then btnEdit.Enabled = False btnDelete.Enabled = False Else btnEdit.Enabled = True btnDelete.Enabled = True Me.odaCustomerIndividual.SelectCommand.Parameters(0).Value = lstCustomers.SelectedItem(0) '- Fill the dataset Me.odaCustomerIndividual.Fill(Me.dsCustomerIndividual, "Customers") End If End Sub Similarly, you will add code to the ActivateEditing subroutine to toggle the Enable property of the various command buttons, depending on their purpose. Listing 1.20 shows the entire routine. Listing 1.20 frmHowTo1_7.vb: Toggling the Enabled Property of btnEdit and btnDelete Buttons Private Sub ActivateEditing(ByVal bEnable As Boolean) Dim oCurr As Object '- Loop through each of the controls on the form For Each oCurr In Me.Controls() '- Check to see if the control is a text box If TypeOf oCurr Is TextBox And oCurr.Name <> "txtCustLimit" Then '- If so, toggle the properties If bEnable Then oCurr.BorderStyle() = _ System.Windows.Forms.BorderStyle.Fixed3D oCurr.BackColor() = System.Drawing.Color.White Else oCurr.BorderStyle() = _ System.Windows.Forms.BorderStyle.FixedSingle oCurr.BackColor() = Me.BackColor End If oCurr.Enabled = bEnable End If Next '- Enable/Disable the appropriate buttons btnEdit.Enabled = Not bEnable btnNew.Enabled = Not bEnable btnDelete.Enabled = Not bEnable btnCancel.Enabled = bEnable btnSave.Enabled = bEnable '- Set the focus to the CustomerID text box If bEnable Then Me.txtCustomerID.Focus() End If End Sub The specific lines of code added are shown here: '- Enable/Disable the appropriate buttons btnEdit.Enabled = Not bEnable btnNew.Enabled = Not bEnable btnDelete.Enabled = Not bEnable btnCancel.Enabled = bEnable btnSave.Enabled = bEnable These buttons are handled as the other buttons are-by taking the opposite value to which bEnable is currently set, and using it to toggle the Enabled property. Finally, if the bEnable flag is True, then focus is moved to the txtCustomerID text box using the following lines of code: '- Set the focus to the CustomerID text box If bEnable Then Me.txtCustomerID.Focus() End If End Sub 2. Add a new command button, with the properties Name and Text set to btnClose and &Close, respectively. Place the code in Listing 1.21 for the Click event. Listing 1.21 frmHowTo1_7.vb: Close the Form Private Sub btnClose_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnClose.Click Me.Close() End Sub 3. Add some code to the Closing event of the form. Listing 1.22 tests whether the btnSave button is enabled. If it is, the MessageBox method is evoked, asking the user if he wants to save changes that were made. If so, then the SaveRecord is called within a Try Catch End Try block. Listing 1.22 frmHowTo1_7.vb: Checking Whether the User Wants to Save a Record Before Closing Private Sub frmHowTo1_7_Closing(ByVal sender As Object, _ ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing '- If an edit or add has been requested, enabling the Save button, ' then prompt to save the record If btnSave.Enabled Then If MessageBox.Show("Would you like to save the current record?", _ "Save Record?", MessageBoxButtons.YesNo) = _ DialogResult.Yes Then Try '- Save the information SaveRecord() Catch saveException As Exception If MessageBox.Show("The following error has occurred: " & saveException.Message & vbCrLf & vbCrLf & _ "Continue with closing the form?", "Error Saving Record", MessageBoxButtons.YesNo) = DialogResult.No Then e.Cancel = True End If End Try End If End If End Sub How It Works In the modifications made to the form in this How-To, many things happen depending on what is occurring. When the user clicks the btnEdit button, btnEdit, btnNew, and btnDelete are disabled, and btnCancel and btnSave are enabled. The opposite is true when btnCancel and btnSave are pressed. If bEnable is True, then the focus is moved to the txtCustomerID text box. When the txtClosed button is clicked, the application then checks whether the btnSave command button has been enabled, meaning data is being edited. If so, then the user is asked whether he wants to save the current record. If the user does, the system then saves the current information back to the server. Comments The tasks displayed in this How-To are just a few of the tasks you can do to make your forms look and feel more professional. They are also what users come to expect from database applications. Play with the form a bit more. You're sure to come up with a few more ideas. . 1.7 Put the Finishing Touches on a Data Bound Form Besides handling the basics, you need to add some finishing touches to a data entry form, such as enabling/disabling. expect from a good data entry form. Although the majority of the major issues are taken care of for the form you created so far in the chapter, your