如何：确保子表中的选定行保持在正确的位置

项目
08/12/2011

在 Windows 窗体中使用数据绑定时，您经常会在父/子视图或主/详细信息视图中显示数据。这表示一个数据绑定方案，其中来自同一源的数据将在两个控件中显示。更改一个控件中的选定内容会导致另一个控件中显示的数据发生更改。例如，第一个控件可能包含一个客户列表，而第二个控件包含与第一个控件中的选定客户相关的订单列表。

从 .NET Framework 2.0 版开始，当您在父/子视图中显示数据时，可能需要执行额外的步骤以确保子表中的当前选定行不会重置为表的第一行。为此，您必须对子表位置进行缓存，并在父表发生更改之后重置子表。通常，当父表行中的字段第一次发生更改时，子表将重置。

对当前子表位置进行缓存

声明一个整数变量以存储子列表位置，并声明一个布尔型变量以存储是否对子列表位置进行缓存。

Private cachedPosition As Integer = - 1
Private cacheChildPosition As Boolean = True

private int cachedPosition = -1;
private bool cacheChildPosition = true;

为绑定的 CurrencyManager 处理 ListChanged 事件，并检查 Reset 的 ListChangedType。

检查 CurrencyManager 的当前位置。如果此当前位置大于列表中的第一个项（通常为 0），则将其保存到一个变量中。

Private Sub relatedCM_ListChanged(ByVal sender As Object, _
    ByVal e As ListChangedEventArgs)
    ' Check to see if this is a caching situation.
    If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
        ' If so, check to see if it is a reset situation, and the current
        ' position is greater than zero.
        Dim relatedCM As CurrencyManager = sender
        If e.ListChangedType = ListChangedType.Reset _
            AndAlso relatedCM.Position > 0 Then

            ' If so, cache the position of the child table.
            cachedPosition = relatedCM.Position
        End If
    End If

End Sub

void relatedCM_ListChanged(object sender, ListChangedEventArgs e)
{
    // Check to see if this is a caching situation.
    if (cacheChildPosition && cachePositionCheckBox.Checked) 
    {
        // If so, check to see if it is a reset situation, and the current
        // position is greater than zero.
        CurrencyManager relatedCM = sender as CurrencyManager;
        if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0)

            // If so, cache the position of the child table.
            cachedPosition = relatedCM.Position;
    }
}

为父级当前项管理器处理父列表的 CurrentChanged 事件。在处理程序中，设置布尔值以指示其不是一个缓存方案。如果发生 CurrentChanged，则对父列表进行的更改是列表位置更改，而不是项值更改。

' Handle the current changed event. This event occurs when
' the current item is changed, but not when a field of the current
' item is changed.
Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _
    ByVal e As EventArgs) Handles bindingSource1.CurrentChanged
    ' If the CurrentChanged event occurs, this is not a caching 
    ' situation.
    cacheChildPosition = False

End Sub

void bindingSource1_CurrentChanged(object sender, EventArgs e)
{
    // If the CurrentChanged event occurs, this is not a caching 
    // situation.
    cacheChildPosition = false;
}

重置子表位置

为子表绑定的 CurrencyManager 处理 PositionChanged 事件。

将子表位置重置为上一过程中保存的已缓存位置。

Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) 
    ' Check to see if this is a caching situation.
    If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
        Dim relatedCM As CurrencyManager = sender

        ' If so, check to see if the current position is 
        ' not equal to the cached position and the cached 
        ' position is not out of bounds.
        If relatedCM.Position <> cachedPosition AndAlso _
            cachedPosition > 0 AndAlso cachedPosition < _
            relatedCM.Count Then
            relatedCM.Position = cachedPosition
            cachedPosition = -1
        End If
    End If
End Sub

void relatedCM_PositionChanged(object sender, EventArgs e)
{
    // Check to see if this is a caching situation.
    if (cacheChildPosition && cachePositionCheckBox.Checked)
    {
        CurrencyManager relatedCM = sender as CurrencyManager;

        // If so, check to see if the current position is 
        // not equal to the cached position and the cached 
        // position is not out of bounds.
        if (relatedCM.Position != cachedPosition && cachedPosition
            > 0 && cachedPosition < relatedCM.Count)
        {
            relatedCM.Position = cachedPosition;
            cachedPosition = -1;
        }
    }
}

示例

下面的示例演示如何为子表在 CurrencyManager 上保存当前位置，并在完成对父表的编辑之后重置该位置。此示例包含两个 DataGridView 控件，这两个控件已分别绑定到使用 BindingSource 组件的 DataSet 中的两个表。这两个表之间建立了关系，并将该关系添加到 DataSet。为了便于演示，最初将子表中的位置设置为第三行。

Imports System
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms



Public Class Form1
    Inherits Form

    Public Sub New() 
        InitializeControlsAndDataSource()

    End Sub

    ' Declare the controls to be used.
    Private WithEvents bindingSource1 As BindingSource
    Private dataGridView1 As DataGridView
    Private WithEvents button1 As Button
    Private dataGridView2 As DataGridView
    Private cachePositionCheckBox As CheckBox
    Public set1 As DataSet


    Private Sub InitializeControlsAndDataSource() 
        ' Initialize the controls and set location, size and 
        ' other basic properties.
        Me.dataGridView1 = New DataGridView()
        Me.bindingSource1 = New BindingSource()
        Me.button1 = New Button()
        Me.dataGridView2 = New DataGridView()
        Me.cachePositionCheckBox = New System.Windows.Forms.CheckBox()
        Me.dataGridView1.ColumnHeadersHeightSizeMode = _
            DataGridViewColumnHeadersHeightSizeMode.AutoSize
        Me.dataGridView1.Dock = DockStyle.Top
        Me.dataGridView1.Location = New Point(0, 20)
        Me.dataGridView1.Size = New Size(292, 170)
        Me.button1.Location = New System.Drawing.Point(18, 175)
        Me.button1.Size = New System.Drawing.Size(125, 23)

        button1.Text = "Clear Parent Field"

        Me.dataGridView2.ColumnHeadersHeightSizeMode = _
            System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize
        Me.dataGridView2.Location = New System.Drawing.Point(0, 225)
        Me.dataGridView2.Size = New System.Drawing.Size(309, 130)
        Me.cachePositionCheckBox.AutoSize = True
        Me.cachePositionCheckBox.Checked = True
        Me.cachePositionCheckBox.Location = New System.Drawing.Point(150, 175)
        Me.cachePositionCheckBox.Name = "radioButton1"
        Me.cachePositionCheckBox.Size = New System.Drawing.Size(151, 17)
        Me.cachePositionCheckBox.Text = "Cache and restore position"
        Me.ClientSize = New System.Drawing.Size(325, 420)
        Me.Controls.Add(Me.dataGridView1)
        Me.Controls.Add(Me.cachePositionCheckBox)
        Me.Controls.Add(Me.dataGridView2)
        Me.Controls.Add(Me.button1)

        ' Initialize the data.
        set1 = InitializeDataSet()

        ' Set the data source to the DataSet.
        bindingSource1.DataSource = set1

        'Set the DataMember to the Menu table.
        bindingSource1.DataMember = "Customers"

        ' Add the control data bindings.
        dataGridView1.DataSource = bindingSource1

        ' Set the data source and member for the second DataGridView.
        dataGridView2.DataSource = bindingSource1
        dataGridView2.DataMember = "custOrders"

        ' Get the currency manager for the customer orders binding.
        Dim relatedCM As CurrencyManager = _
            bindingSource1.GetRelatedCurrencyManager("custOrders")

        ' Handle the two events for caching and resetting the position.
        AddHandler relatedCM.ListChanged, AddressOf relatedCM_ListChanged
        AddHandler relatedCM.PositionChanged, AddressOf relatedCM_PositionChanged

        ' Set the position in the child table for demonstration purposes.
        relatedCM.Position = 3

        ' Set cacheing to true in case current changed event
        ' occured on set up.
        cacheChildPosition = True


    End Sub 'InitializeControlsAndDataSource



    ' Establish the data set with two tables and a relationship
    ' between them.
    Private Function InitializeDataSet() As DataSet 
        set1 = New DataSet()
        ' Declare the DataSet and add a table and column.
        set1.Tables.Add("Customers")
        set1.Tables(0).Columns.Add("CustomerID")
        set1.Tables(0).Columns.Add("Customer Name")
        set1.Tables(0).Columns.Add("Contact Name")

        ' Add some rows to the table.
        set1.Tables("Customers").Rows.Add("c1", "Fabrikam, Inc.", _
            "Ellen Adams")
        set1.Tables(0).Rows.Add("c2", "Lucerne Publishing", "Don Hall")
        set1.Tables(0).Rows.Add("c3", "Northwind Traders", "Lori Penor")
        set1.Tables(0).Rows.Add("c4", "Tailspin Toys", "Michael Patten")
        set1.Tables(0).Rows.Add("c5", "Woodgrove Bank", "Jyothi Pai")

        ' Declare the DataSet and add a table and column.
        set1.Tables.Add("Orders")
        set1.Tables(1).Columns.Add("CustomerID")
        set1.Tables(1).Columns.Add("OrderNo")
        set1.Tables(1).Columns.Add("OrderDate")

        ' Add some rows to the table.
        set1.Tables(1).Rows.Add("c1", "119", "10/04/2006")
        set1.Tables(1).Rows.Add("c1", "149", "10/10/2006")
        set1.Tables(1).Rows.Add("c1", "159", "10/12/2006")
        set1.Tables(1).Rows.Add("c2", "169", "10/10/2006")
        set1.Tables(1).Rows.Add("c2", "179", "10/10/2006")
        set1.Tables(1).Rows.Add("c2", "189", "10/12/2006")
        set1.Tables(1).Rows.Add("c3", "122", "10/04/2006")
        set1.Tables(1).Rows.Add("c4", "130", "10/10/2006")
        set1.Tables(1).Rows.Add("c5", "1.29", "10/14/2006")

        Dim dr As New DataRelation("custOrders", _
            set1.Tables("Customers").Columns("CustomerID"), _
            set1.Tables("Orders").Columns("CustomerID"))
        set1.Relations.Add(dr)
        Return set1

    End Function '
    Private cachedPosition As Integer = - 1
    Private cacheChildPosition As Boolean = True

    Private Sub relatedCM_ListChanged(ByVal sender As Object, _
        ByVal e As ListChangedEventArgs)
        ' Check to see if this is a caching situation.
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
            ' If so, check to see if it is a reset situation, and the current
            ' position is greater than zero.
            Dim relatedCM As CurrencyManager = sender
            If e.ListChangedType = ListChangedType.Reset _
                AndAlso relatedCM.Position > 0 Then

                ' If so, cache the position of the child table.
                cachedPosition = relatedCM.Position
            End If
        End If

    End Sub

    ' Handle the current changed event. This event occurs when
    ' the current item is changed, but not when a field of the current
    ' item is changed.
    Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _
        ByVal e As EventArgs) Handles bindingSource1.CurrentChanged
        ' If the CurrentChanged event occurs, this is not a caching 
        ' situation.
        cacheChildPosition = False

    End Sub

    Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) 
        ' Check to see if this is a caching situation.
        If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
            Dim relatedCM As CurrencyManager = sender

            ' If so, check to see if the current position is 
            ' not equal to the cached position and the cached 
            ' position is not out of bounds.
            If relatedCM.Position <> cachedPosition AndAlso _
                cachedPosition > 0 AndAlso cachedPosition < _
                relatedCM.Count Then
                relatedCM.Position = cachedPosition
                cachedPosition = -1
            End If
        End If
    End Sub

    Private count As Integer = 0

    Private Sub button1_Click(ByVal sender As Object, _
        ByVal e As EventArgs) Handles button1.Click
        ' For demo purposes--modifies a value in the first row of the
        ' parent table.
        Dim row1 As DataRow = set1.Tables(0).Rows(0)
        row1(1) = DBNull.Value
    End Sub

    <STAThread()>  _
    Shared Sub Main() 
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Application.Run(New Form1())

    End Sub
End Class

using System;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace BT2
{
    public class Form1 : Form
    {
        public Form1()
        {
            InitializeControlsAndDataSource();
        }

        // Declare the controls to be used.
        private BindingSource bindingSource1;
        private DataGridView dataGridView1;
        private Button button1;
        private DataGridView dataGridView2;
        private CheckBox cachePositionCheckBox;
        public DataSet set1;

        private void InitializeControlsAndDataSource()
        {
            // Initialize the controls and set location, size and 
            // other basic properties.
            this.dataGridView1 = new DataGridView();
            this.bindingSource1 = new BindingSource();
            this.button1 = new Button();
            this.dataGridView2 = new DataGridView();
            this.cachePositionCheckBox = new System.Windows.Forms.CheckBox();
            this.dataGridView1.ColumnHeadersHeightSizeMode =
                DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            this.dataGridView1.Dock = DockStyle.Top;
            this.dataGridView1.Location = new Point(0, 20);
            this.dataGridView1.Size = new Size(292, 170);
            this.button1.Location = new System.Drawing.Point(18, 175);
            this.button1.Size = new System.Drawing.Size(125, 23);

            button1.Text = "Clear Parent Field";
            this.button1.Click += new System.EventHandler(this.button1_Click);
            this.dataGridView2.ColumnHeadersHeightSizeMode = 
                System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
            this.dataGridView2.Location = new System.Drawing.Point(0, 225);
            this.dataGridView2.Size = new System.Drawing.Size(309, 130);
            this.cachePositionCheckBox.AutoSize = true;
            this.cachePositionCheckBox.Checked = true;
            this.cachePositionCheckBox.Location = new System.Drawing.Point(150, 175);
            this.cachePositionCheckBox.Name = "radioButton1";
            this.cachePositionCheckBox.Size = new System.Drawing.Size(151, 17);
            this.cachePositionCheckBox.Text = "Cache and restore position";
            this.ClientSize = new System.Drawing.Size(325, 420);
            this.Controls.Add(this.dataGridView1);
            this.Controls.Add(this.cachePositionCheckBox);
            this.Controls.Add(this.dataGridView2);
            this.Controls.Add(this.button1);

            // Initialize the data.
            set1 = InitializeDataSet();

            // Set the data source to the DataSet.
            bindingSource1.DataSource = set1;

            //Set the DataMember to the Menu table.
            bindingSource1.DataMember = "Customers";

            // Add the control data bindings.
            dataGridView1.DataSource = bindingSource1;

            // Set the data source and member for the second DataGridView.
            dataGridView2.DataSource = bindingSource1;
            dataGridView2.DataMember = "custOrders";

            // Get the currency manager for the customer orders binding.
            CurrencyManager relatedCM = 
                bindingSource1.GetRelatedCurrencyManager("custOrders");

            // Set the position in the child table for demonstration purposes.
            relatedCM.Position = 3;

            // Handle the current changed event. This event occurs when
            // the current item is changed, but not when a field of the current
            // item is changed.
            bindingSource1.CurrentChanged += 
                new EventHandler(bindingSource1_CurrentChanged);

            // Handle the two events for caching and resetting the position.
            relatedCM.ListChanged += new ListChangedEventHandler(relatedCM_ListChanged);
            relatedCM.PositionChanged
                += new EventHandler(relatedCM_PositionChanged);

            // Set cacheing to true in case current changed event
            // occured on set up.
            cacheChildPosition = true;
        }


        // Establish the data set with two tables and a relationship
        // between them.
        private DataSet InitializeDataSet()
        {
            set1 = new DataSet();
            // Declare the DataSet and add a table and column.
            set1.Tables.Add("Customers");
            set1.Tables[0].Columns.Add("CustomerID");
            set1.Tables[0].Columns.Add("Customer Name");
            set1.Tables[0].Columns.Add("Contact Name");

            // Add some rows to the table.
            set1.Tables["Customers"].Rows.Add("c1", "Fabrikam, Inc.", "Ellen Adams");
            set1.Tables[0].Rows.Add("c2", "Lucerne Publishing", "Don Hall");
            set1.Tables[0].Rows.Add("c3", "Northwind Traders", "Lori Penor");
            set1.Tables[0].Rows.Add("c4", "Tailspin Toys", "Michael Patten");
            set1.Tables[0].Rows.Add("c5", "Woodgrove Bank", "Jyothi Pai");

            // Declare the DataSet and add a table and column.
            set1.Tables.Add("Orders");
            set1.Tables[1].Columns.Add("CustomerID");
            set1.Tables[1].Columns.Add("OrderNo");
            set1.Tables[1].Columns.Add("OrderDate");

            // Add some rows to the table.
            set1.Tables[1].Rows.Add("c1", "119", "10/04/2006");
            set1.Tables[1].Rows.Add("c1", "149", "10/10/2006");
            set1.Tables[1].Rows.Add("c1", "159", "10/12/2006");
            set1.Tables[1].Rows.Add("c2", "169", "10/10/2006");
            set1.Tables[1].Rows.Add("c2", "179", "10/10/2006");
            set1.Tables[1].Rows.Add("c2", "189", "10/12/2006");
            set1.Tables[1].Rows.Add("c3", "122", "10/04/2006");
            set1.Tables[1].Rows.Add("c4", "130", "10/10/2006");
            set1.Tables[1].Rows.Add("c5", "1.29", "10/14/2006");

            DataRelation dr = new DataRelation("custOrders",
                set1.Tables["Customers"].Columns["CustomerID"],
                set1.Tables["Orders"].Columns["CustomerID"]);
            set1.Relations.Add(dr);
            return set1;
        }
        private int cachedPosition = -1;
        private bool cacheChildPosition = true;

        void relatedCM_ListChanged(object sender, ListChangedEventArgs e)
        {
            // Check to see if this is a caching situation.
            if (cacheChildPosition && cachePositionCheckBox.Checked) 
            {
                // If so, check to see if it is a reset situation, and the current
                // position is greater than zero.
                CurrencyManager relatedCM = sender as CurrencyManager;
                if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0)

                    // If so, cache the position of the child table.
                    cachedPosition = relatedCM.Position;
            }
        }
        void bindingSource1_CurrentChanged(object sender, EventArgs e)
        {
            // If the CurrentChanged event occurs, this is not a caching 
            // situation.
            cacheChildPosition = false;
        }
        void relatedCM_PositionChanged(object sender, EventArgs e)
        {
            // Check to see if this is a caching situation.
            if (cacheChildPosition && cachePositionCheckBox.Checked)
            {
                CurrencyManager relatedCM = sender as CurrencyManager;

                // If so, check to see if the current position is 
                // not equal to the cached position and the cached 
                // position is not out of bounds.
                if (relatedCM.Position != cachedPosition && cachedPosition
                    > 0 && cachedPosition < relatedCM.Count)
                {
                    relatedCM.Position = cachedPosition;
                    cachedPosition = -1;
                }
            }
        }
        int count = 0;
        private void button1_Click(object sender, EventArgs e)
        {
            // For demo purposes--modifies a value in the first row of the
            // parent table.
            DataRow row1 = set1.Tables[0].Rows[0];
            row1[1] = DBNull.Value;

        }

        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }


}

若要测试代码示例，请执行以下步骤：

运行该示例。
确保选中**“缓存并重置位置”**复选框。
单击**“清除父字段”**按钮会导致父表中的字段发生更改。请注意，子表中的选定行不会发生更改。
关闭示例，然后再次运行该示例。您必须这样做，因为重置行为仅在父表行中第一次发生更改时发生。
清除**“缓存并重置位置”**复选框。
单击**“清除父字段”**按钮。请注意，子表中的选定行将变为第一行。

编译代码

此示例需要：

对 System、System.Data、System.Drawing、System.Windows.Forms 和 System.XML 程序集的引用。

有关如何从 Visual Basic 或 Visual C# 的命令行生成此示例的信息，请参见从命令行生成 (Visual Basic) 或在命令行上使用 csc.exe 生成。也可以通过将代码粘贴到新项目，使用 Visual Studio 生成此示例。有关更多信息，请参见如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例和如何：使用 Visual Studio 编译和运行完整的 Windows 窗体代码示例.

请参见

通过

如何：确保子表中的选定行保持在正确的位置

对当前子表位置进行缓存

重置子表位置

示例

编译代码

请参见

任务

概念

其他资源

其他资源