System.Data.DataRowView返回XML没有价值

Question

我试图从具有相同的名称，但这里不同的ID两个XML元素得到不同的价值观是我的代码：

<?xml version="1.0" encoding="utf-8"?> 
<Vehicle_data> 
    <Data ID="1"> 
    <Vehicle_name>bullet</Vehicle_name> 
    <Owner_name>qwe</Owner_name> 
    <Number_plate>q2236</Number_plate> 
    <Insurance_laps_date>qwe</Insurance_laps_date> 
    <Chassis_no>wqe</Chassis_no> 
    <Driving_lic_no>q</Driving_lic_no> 
    <Entry_date>05-09-15</Entry_date> 
    <Entry_time>08:36:52</Entry_time> 
    </Data> 
    <Data ID="2"> 
    <Vehicle_name>optra</Vehicle_name> 
    <Owner_name>ott</Owner_name> 
    <Number_plate>qwerte</Number_plate> 
    <Insurance_laps_date>gdsfg</Insurance_laps_date> 
    <Chassis_no>dfgdf</Chassis_no> 
    <Driving_lic_no>dfgdf</Driving_lic_no> 
    <Entry_date>05-09-15</Entry_date> 
    <Entry_time>08:38:34</Entry_time> 
    </Data> 
    <Data ID="3"> 
    <Vehicle_name>enzo</Vehicle_name> 
    <Owner_name>asd</Owner_name> 
    <Number_plate>awda</Number_plate> 
    <Insurance_laps_date>adaw</Insurance_laps_date> 
    <Chassis_no>awdw</Chassis_no> 
    <Driving_lic_no>adaw</Driving_lic_no> 
    <Entry_date>05-09-15</Entry_date> 
    <Entry_time>08:40:26</Entry_time> 
    </Data> 
    <Data ID="4"> 
    <Vehicle_name>enzo</Vehicle_name> 
    <Owner_name>kok</Owner_name> 
    <Number_plate>asdasd</Number_plate> 
    <Insurance_laps_date>asfdadsad</Insurance_laps_date> 
    <Chassis_no>dasdasd</Chassis_no> 
    <Driving_lic_no>asdasdas</Driving_lic_no> 
    <Entry_date>05-09-15</Entry_date> 
    <Entry_time>08:42:05</Entry_time> 
    </Data> 
</Vehicle_data> 

这个我用下面的代码的VB当窗体加载

Dim doc As XDocument = XDocument.Load(Environment.CurrentDirectory & "\Vehicle_data.xml") 

Dim dt As New DataTable 
dt.Columns.Add("Name") 
dt.Columns.Add("ID") 

For Each itm In doc.Descendants("Vehicle_name") 
    Dim dr As DataRow = dt.NewRow 
    dr("Name") = itm.Value 
    dr("ID") = itm.Parent.FirstAttribute.Value 
    dt.Rows.Add(dr) 
Next 

ComboBox1.DataSource = dt 
ComboBox1.DisplayMember = "Name" 
ComboBox1.ValueMember = "ID" 

在ComboBox1.SelectedIndexChanged事件：

Dim doc As XDocument = XDocument.Load(Environment.CurrentDirectory & "\Vehicle_data.xml") 

If ComboBox1.SelectedItem.ToString <> "System.Data.DataRowView" AndAlso _ 
    ComboBox1.SelectedValue.ToString <> "System.Data.DataRowView" Then 

    Dim vehicledata = From el In doc.Element("Vehicle_data").Elements("Data") _ 
     Where (el.Element("Vehicle_name") = ComboBox1.SelectedItem.ToString) _ 
     Select New With 
     { 
      .VName = el.Element("Vehicle_name").Value, _ 
      .onr = el.Element("Owner_name").Value, _ 
      .nopl = el.Element("Number_plate").Value, _ 
      .ins = el.Element("Insurance_laps_date").Value, _ 
      .chassis = el.Element("Chassis_no").Value, _ 
      .lic = el.Element("Driving_lic_no").Value, _ 
      .PID = el.Element("Chassis_no").Parent.FirstAttribute.Value 
     } 

    For Each el In vehicledata 
     If ComboBox1.SelectedValue.ToString = el.PID Then 
      TextBox5.Text = el.VName 
      TextBox1.Text = el.onr 
      TextBox2.Text = el.nopl 
      TextBox3.Text = el.ins 
      TextBox4.Text = el.chassis 
      TextBox6.Text = el.lic 
     End If 
    Next 
End If 

我认为el.PID没有返回任何值。 请帮帮我。

Answer 1

ComboBox1.SelectedItem.ToString将总是等于"System.Data.DataRowView"，所以它永远不会进入你的if声明。不知道为什么你有那个if。是否在期间停止运行该代码？如果是这样，那么您应该使用SelectionChangeCommitted事件而不是SelectedIndexChanged。

没有这种if创建一个新的方法：

Private Sub SetControlValues() 

    Dim doc As XDocument = XDocument.Load(Environment.CurrentDirectory & "\Vehicle_data.xml") 

    Dim vehicledata = From el In doc.Element("Vehicle_data").Elements("Data") _ 
     Where (el.Attribute("ID") = ComboBox1.SelectedValue.ToString) _ 
     Select New With 
     { 
      .VName = el.Element("Vehicle_name").Value, _ 
      .onr = el.Element("Owner_name").Value, _ 
      .nopl = el.Element("Number_plate").Value, _ 
      .ins = el.Element("Insurance_laps_date").Value, _ 
      .chassis = el.Element("Chassis_no").Value, _ 
      .lic = el.Element("Driving_lic_no").Value, _ 
      .PID = el.Element("Chassis_no").Parent.FirstAttribute.Value 
     } 

    For Each el In vehicledata 
     If ComboBox1.SelectedValue.ToString = el.PID Then 
      TextBox5.Text = el.VName 
      TextBox1.Text = el.onr 
      TextBox2.Text = el.nopl 
      TextBox3.Text = el.ins 
      TextBox4.Text = el.chassis 
      TextBox6.Text = el.lic 
     End If 
    Next 
End Sub 

还要注意更新Where，你需要比较SelectedValue到ID属性。

取出SelectedIndexChanged事件并添加新的SelectionChangedCommitted事件，只需调用上述方法：

Private Sub ComboBox1_SelectionChangeCommitted(sender As Object, e As EventArgs) Handles ComboBox1.SelectionChangeCommitted 
    SetControlValues() 
End Sub 

最后，窗体加载过程中初始化文本框，添加一个调用SetControlValues()作为最后一行的。