第三课 设计数据库交互处理逻辑

　　本课描述如此编写增删改代码，实现与数据库的交互。

示例文件：

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上一课

21、转到MainPage.xaml中，在DataGrid控件的右侧设计数据编辑区域的若干控件；

22、将右侧的TextBox控件的Text属性和DatePicker控件的SelectedDate属性逐一绑定到DataGrid控件的SelectedItem的相关路径上。其中班级ID文本框控件的Text属性绑定到cob班级ID的SelectedValue路径上；

23、保存并生成解决方案，然后按F5测试，测试效果为选中DataGrid的记录后，右侧编辑区域将数据呈现出来。

图示08：

24、转到MainPage.xaml.vb中，编写增删改的处理逻辑，代码如下：

    Private Sub OnSubmitCompleted(ByVal so As SubmitOperation)
        '增删改时，通过SubmitChanges方法绑定该事件，以完成提交返回后的操作。
        SetDataGrid()
    End Sub

    Private Sub btn新增_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btn新增.Click
        If String.IsNullOrEmpty(txt班级ID.Text) Then Exit Sub
        Dim student As New 学生表
        student.姓名 = txt姓名.Text
        student.性别 = txt性别.Text
        If date生日.SelectedDate Is Nothing = False Then
            student.生日 = date生日.SelectedDate
        End If
        student.班级ID = CInt(txt班级ID.Text)
        myD.学生表s.Add(student)
        myD.SubmitChanges(AddressOf OnSubmitCompleted, Nothing) '提交数据并绑定OnSubmitCompleted事件
    End Sub

    Private Sub btn修改_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btn修改.Click
        If String.IsNullOrEmpty(txt学生ID.Text) Then Exit Sub
        Dim student As New 学生表
        student = myD.学生表s.Single(Function(x) x.学生ID = CInt(txt学生ID.Text))
        student.姓名 = txt姓名.Text
        student.性别 = txt性别.Text
        If date生日.SelectedDate Is Nothing = False Then
            student.生日 = date生日.SelectedDate
        End If
        myD.SubmitChanges(AddressOf OnSubmitCompleted, Nothing) '提交数据并绑定OnSubmitCompleted事件
    End Sub

    Private Sub btn删除_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btn删除.Click
        If String.IsNullOrEmpty(txt学生ID.Text) Then Exit Sub
        Dim student As New 学生表
        student = myD.学生表s.Single(Function(x) x.学生ID = CInt(txt学生ID.Text))
        myD.学生表s.Remove(student)
        myD.SubmitChanges(AddressOf OnSubmitCompleted, Nothing) '提交数据并绑定OnSubmitCompleted事件
    End Sub

    Private Sub DataGrid1_GotFocus(sender As Object, e As System.Windows.RoutedEventArgs) Handles DataGrid1.GotFocus
        ResetDatePickerBinding()
    End Sub

    Private Sub ResetDatePickerBinding()
        'DatePicker控件在选择日期后，原在xaml中设置的绑定失效，需重新设置
        Dim b As Binding = New Binding("SelectedItem.生日")
        b.ElementName = "DataGrid1"
        b.Mode = BindingMode.OneWay
        date生日.SetBinding(DatePicker.SelectedDateProperty, b)
    End Sub

25、保存、生成、测试运行。

图示09：