演练：在 Windows 窗体 DataGridView 控件中实现虚拟模式

  • 项目

如果要在 DataGridView 控件中显示大量表格数据，可以将 VirtualMode 属性设置为 true 并显式管理控件与其数据存储的交互。 这样，便可以在此情况下微调控件的性能。

DataGridView 控件提供了几个事件，你可以处理这些事件以与自定义数据存储进行交互。 此演练将指导你完成实现这些事件处理程序的过程。 本主题中的代码示例使用非常简单的数据源进行说明。 在生产设置中，通常只加载需要显示在缓存中的行，并处理 DataGridView 事件以与缓存交互和更新缓存。 有关更多信息，请参阅在 Windows 窗体 DataGridView 控件中实现实时数据加载的虚拟模式

若要将本主题中的代码复制为单个列表，请参阅如何：在 Windows 窗体 DataGridView 控件中实现虚拟模式。

创建窗体

实现虚拟模式

  1. 创建一个派生自 Form 并包含 DataGridView 控件的类。

    以下代码包含一些基本初始化。 它声明一些变量，这些变量将在后续步骤中使用，提供 Main 方法，并在类构造函数中提供简单的窗体布局。

    #using <System.Drawing.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>

using namespace System;
using namespace System::Windows::Forms;

public ref class Customer
{
private:
   String^ companyNameValue;
   String^ contactNameValue;

public:
   Customer()
   {
      
      // Leave fields empty.
   }

   Customer( String^ companyName, String^ contactName )
   {
      companyNameValue = companyName;
      contactNameValue = contactName;
   }


   property String^ CompanyName 
   {
      String^ get()
      {
         return companyNameValue;
      }

      void set( String^ value )
      {
         companyNameValue = value;
      }

   }

   property String^ ContactName 
   {
      String^ get()
      {
         return contactNameValue;
      }

      void set( String^ value )
      {
         contactNameValue = value;
      }

   }

};

public ref class Form1: public Form
{
private:
   DataGridView^ dataGridView1;

   // Declare an ArrayList to serve as the data store. 
   System::Collections::ArrayList^ customers;

   // Declare a Customer object to store data for a row being edited.
   Customer^ customerInEdit;

   // Declare a variable to store the index of a row being edited. 
   // A value of -1 indicates that there is no row currently in edit. 
   int rowInEdit;

   // Declare a variable to indicate the commit scope. 
   // Set this value to false to use cell-level commit scope. 
   bool rowScopeCommit;

public:
   static void Main()
   {
      Application::Run( gcnew Form1 );
   }

   Form1()
   {
      dataGridView1 = gcnew DataGridView;
      customers = gcnew System::Collections::ArrayList;
      rowInEdit = -1;
      rowScopeCommit = true;
      
      // Initialize the form.
      this->dataGridView1->Dock = DockStyle::Fill;
      this->Controls->Add( this->dataGridView1 );
      this->Load += gcnew EventHandler( this, &Form1::Form1_Load );
   }

private:

    using System;
using System.Windows.Forms;

public class Form1 : Form
{
    private DataGridView dataGridView1 = new DataGridView();

    // Declare an ArrayList to serve as the data store.
    private System.Collections.ArrayList customers =
        new System.Collections.ArrayList();

    // Declare a Customer object to store data for a row being edited.
    private Customer customerInEdit;

    // Declare a variable to store the index of a row being edited.
    // A value of -1 indicates that there is no row currently in edit.
    private int rowInEdit = -1;

    // Declare a variable to indicate the commit scope.
    // Set this value to false to use cell-level commit scope.
    private bool rowScopeCommit = true;

    [STAThreadAttribute()]
    public static void Main()
    {
        Application.Run(new Form1());
    }

    public Form1()
    {
        // Initialize the form.
        this.dataGridView1.Dock = DockStyle.Fill;
        this.Controls.Add(this.dataGridView1);
        this.Load += new EventHandler(Form1_Load);
        this.Text = "DataGridView virtual-mode demo (row-level commit scope)";
    }

    Imports System.Windows.Forms

Public Class Form1
    Inherits Form

    Private WithEvents dataGridView1 As New DataGridView()

    ' Declare an ArrayList to serve as the data store. 
    Private customers As New System.Collections.ArrayList()

    ' Declare a Customer object to store data for a row being edited.
    Private customerInEdit As Customer

    ' Declare a variable to store the index of a row being edited. 
    ' A value of -1 indicates that there is no row currently in edit. 
    Private rowInEdit As Integer = -1

    ' Declare a variable to indicate the commit scope. 
    ' Set this value to false to use cell-level commit scope. 
    Private rowScopeCommit As Boolean = True

    <STAThreadAttribute()> _
    Public Shared Sub Main()
        Application.Run(New Form1())
    End Sub

    Public Sub New()
        ' Initialize the form.
        Me.dataGridView1.Dock = DockStyle.Fill
        Me.Controls.Add(Me.dataGridView1)
        Me.Text = "DataGridView virtual-mode demo (row-level commit scope)"
    End Sub

    };

int main()
{
   Form1::Main();
}

    }

    
End Class

  2. 为窗体的 Load 事件实现处理程序，该处理程序初始化 DataGridView 控件并使用示例值填充数据存储。

    void Form1_Load( Object^ /*sender*/, EventArgs^ /*e*/ )
{
   
   // Enable virtual mode.
   this->dataGridView1->VirtualMode = true;
   
   // Connect the virtual-mode events to event handlers. 
   this->dataGridView1->CellValueNeeded += gcnew
       DataGridViewCellValueEventHandler( this, &Form1::dataGridView1_CellValueNeeded );
   this->dataGridView1->CellValuePushed += gcnew
       DataGridViewCellValueEventHandler( this, &Form1::dataGridView1_CellValuePushed );
   this->dataGridView1->NewRowNeeded += gcnew
       DataGridViewRowEventHandler( this, &Form1::dataGridView1_NewRowNeeded );
   this->dataGridView1->RowValidated += gcnew
       DataGridViewCellEventHandler( this, &Form1::dataGridView1_RowValidated );
   this->dataGridView1->RowDirtyStateNeeded += gcnew
       QuestionEventHandler( this, &Form1::dataGridView1_RowDirtyStateNeeded );
   this->dataGridView1->CancelRowEdit += gcnew
       QuestionEventHandler( this, &Form1::dataGridView1_CancelRowEdit );
   this->dataGridView1->UserDeletingRow += gcnew
       DataGridViewRowCancelEventHandler( this, &Form1::dataGridView1_UserDeletingRow );
   
   // Add columns to the DataGridView.
   DataGridViewTextBoxColumn^ companyNameColumn = gcnew DataGridViewTextBoxColumn;
   companyNameColumn->HeaderText = L"Company Name";
   companyNameColumn->Name = L"Company Name";
   DataGridViewTextBoxColumn^ contactNameColumn = gcnew DataGridViewTextBoxColumn;
   contactNameColumn->HeaderText = L"Contact Name";
   contactNameColumn->Name = L"Contact Name";
   this->dataGridView1->Columns->Add( companyNameColumn );
   this->dataGridView1->Columns->Add( contactNameColumn );
   this->dataGridView1->AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode::DisplayedCells;
   
   // Add some sample entries to the data store. 
   this->customers->Add( gcnew Customer( L"Bon app'",L"Laurence Lebihan" ) );
   this->customers->Add( gcnew Customer( L"Bottom-Dollar Markets",L"Elizabeth Lincoln" ) );
   this->customers->Add( gcnew Customer( L"B's Beverages",L"Victoria Ashworth" ) );
   
   // Set the row count, including the row for new records.
   this->dataGridView1->RowCount = 4;
}

    private void Form1_Load(object sender, EventArgs e)
{
    // Enable virtual mode.
    this.dataGridView1.VirtualMode = true;

    // Connect the virtual-mode events to event handlers.
    this.dataGridView1.CellValueNeeded += new
        DataGridViewCellValueEventHandler(dataGridView1_CellValueNeeded);
    this.dataGridView1.CellValuePushed += new
        DataGridViewCellValueEventHandler(dataGridView1_CellValuePushed);
    this.dataGridView1.NewRowNeeded += new
        DataGridViewRowEventHandler(dataGridView1_NewRowNeeded);
    this.dataGridView1.RowValidated += new
        DataGridViewCellEventHandler(dataGridView1_RowValidated);
    this.dataGridView1.RowDirtyStateNeeded += new
        QuestionEventHandler(dataGridView1_RowDirtyStateNeeded);
    this.dataGridView1.CancelRowEdit += new
        QuestionEventHandler(dataGridView1_CancelRowEdit);
    this.dataGridView1.UserDeletingRow += new
        DataGridViewRowCancelEventHandler(dataGridView1_UserDeletingRow);

    // Add columns to the DataGridView.
    DataGridViewTextBoxColumn companyNameColumn = new
        DataGridViewTextBoxColumn();
    companyNameColumn.HeaderText = "Company Name";
    companyNameColumn.Name = "Company Name";
    DataGridViewTextBoxColumn contactNameColumn = new
        DataGridViewTextBoxColumn();
    contactNameColumn.HeaderText = "Contact Name";
    contactNameColumn.Name = "Contact Name";
    this.dataGridView1.Columns.Add(companyNameColumn);
    this.dataGridView1.Columns.Add(contactNameColumn);
    this.dataGridView1.AutoSizeColumnsMode =
        DataGridViewAutoSizeColumnsMode.DisplayedCells;

    // Add some sample entries to the data store.
    this.customers.Add(new Customer(
        "Bon app'", "Laurence Lebihan"));
    this.customers.Add(new Customer(
        "Bottom-Dollar Markets", "Elizabeth Lincoln"));
    this.customers.Add(new Customer(
        "B's Beverages", "Victoria Ashworth"));

    // Set the row count, including the row for new records.
    this.dataGridView1.RowCount = 4;
}

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) _
    Handles Me.Load

    ' Enable virtual mode.
    Me.dataGridView1.VirtualMode = True

    ' Add columns to the DataGridView.
    Dim companyNameColumn As New DataGridViewTextBoxColumn()
    With companyNameColumn
        .HeaderText = "Company Name"
        .Name = "Company Name"
    End With
    Dim contactNameColumn As New DataGridViewTextBoxColumn()
    With contactNameColumn
        .HeaderText = "Contact Name"
        .Name = "Contact Name"
    End With
    Me.dataGridView1.Columns.Add(companyNameColumn)
    Me.dataGridView1.Columns.Add(contactNameColumn)
    Me.dataGridView1.AutoSizeColumnsMode = _
    DataGridViewAutoSizeColumnsMode.DisplayedCells

    ' Add some sample entries to the data store. 
    Me.customers.Add(New Customer("Bon app'", "Laurence Lebihan"))
    Me.customers.Add(New Customer("Bottom-Dollar Markets", _
        "Elizabeth Lincoln"))
    Me.customers.Add(New Customer("B's Beverages", "Victoria Ashworth"))

    ' Set the row count, including the row for new records.
    Me.dataGridView1.RowCount = 4

End Sub

  3. 为从数据存储或当前正在编辑的 Customer 对象中检索请求的单元格值的 CellValueNeeded 事件实现处理程序。

    只要 DataGridView 控件需要绘制单元格，就会发生此事件。

    void dataGridView1_CellValueNeeded( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellValueEventArgs^ e )
{
   Customer^ customerTmp = nullptr;
   
   // Store a reference to the Customer object for the row being painted.
   if ( e->RowIndex == rowInEdit )
   {
      customerTmp = this->customerInEdit;
   }
   else
   {
      customerTmp = dynamic_cast<Customer^>(this->customers[ e->RowIndex ]);
   }
   
   // Set the cell value to paint using the Customer object retrieved.
   int switchcase = 0;
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Company Name" ) )
         switchcase = 1;
   else
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Contact Name" ) )
         switchcase = 2;


   switch ( switchcase )
   {
      case 1:
         e->Value = customerTmp->CompanyName;
         break;

      case 2:
         e->Value = customerTmp->ContactName;
         break;
   }
}



    private void dataGridView1_CellValueNeeded(object sender,
    System.Windows.Forms.DataGridViewCellValueEventArgs e)
{
    // If this is the row for new records, no values are needed.
    if (e.RowIndex == this.dataGridView1.RowCount - 1) return;

    Customer customerTmp = null;

    // Store a reference to the Customer object for the row being painted.
    if (e.RowIndex == rowInEdit)
    {
        customerTmp = this.customerInEdit;
    }
    else
    {
        customerTmp = (Customer)this.customers[e.RowIndex];
    }

    // Set the cell value to paint using the Customer object retrieved.
    switch (this.dataGridView1.Columns[e.ColumnIndex].Name)
    {
        case "Company Name":
            e.Value = customerTmp.CompanyName;
            break;

        case "Contact Name":
            e.Value = customerTmp.ContactName;
            break;
    }
}

    Private Sub dataGridView1_CellValueNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellValueEventArgs) _
    Handles dataGridView1.CellValueNeeded

    ' If this is the row for new records, no values are needed.
    If e.RowIndex = Me.dataGridView1.RowCount - 1 Then
        Return
    End If

    Dim customerTmp As Customer = Nothing

    ' Store a reference to the Customer object for the row being painted.
    If e.RowIndex = rowInEdit Then
        customerTmp = Me.customerInEdit
    Else
        customerTmp = CType(Me.customers(e.RowIndex), Customer)
    End If

    ' Set the cell value to paint using the Customer object retrieved.
    Select Case Me.dataGridView1.Columns(e.ColumnIndex).Name
        Case "Company Name"
            e.Value = customerTmp.CompanyName

        Case "Contact Name"
            e.Value = customerTmp.ContactName
    End Select

End Sub

  4. 为将已编辑的单元格值存储在表示已编辑行的 Customer 对象中的 CellValuePushed 事件实现处理程序。 每当用户提交单元格值更改时，就会发生此事件。

    void dataGridView1_CellValuePushed( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellValueEventArgs^ e )
{
   Customer^ customerTmp = nullptr;
   
   // Store a reference to the Customer object for the row being edited.
   if ( e->RowIndex < this->customers->Count )
   {
      
      // If the user is editing a new row, create a new Customer object.
      if ( this->customerInEdit == nullptr )
      {
         this->customerInEdit = gcnew Customer(
             (dynamic_cast<Customer^>(this->customers[ e->RowIndex ]))->CompanyName,
             (dynamic_cast<Customer^>(this->customers[ e->RowIndex ])->ContactName) );
      }

      customerTmp = this->customerInEdit;
      this->rowInEdit = e->RowIndex;
   }
   else
   {
      customerTmp = this->customerInEdit;
   }

   
   // Set the appropriate Customer property to the cell value entered.
   int switchcase = 0;
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Company Name" ) )
         switchcase = 1;
   else
   if ( (this->dataGridView1->Columns[ e->ColumnIndex ]->Name)->Equals( L"Contact Name" ) )
         switchcase = 2;


   switch ( switchcase )
   {
      case 1:
         customerTmp->CompanyName = dynamic_cast<String^>(e->Value);
         break;

      case 2:
         customerTmp->ContactName = dynamic_cast<String^>(e->Value);
         break;
   }
}



    private void dataGridView1_CellValuePushed(object sender,
    System.Windows.Forms.DataGridViewCellValueEventArgs e)
{
    Customer customerTmp = null;

    // Store a reference to the Customer object for the row being edited.
    if (e.RowIndex < this.customers.Count)
    {
        // If the user is editing a new row, create a new Customer object.
        this.customerInEdit ??= new Customer(
            ((Customer)this.customers[e.RowIndex]).CompanyName,
            ((Customer)this.customers[e.RowIndex]).ContactName);
        customerTmp = this.customerInEdit;
        this.rowInEdit = e.RowIndex;
    }
    else
    {
        customerTmp = this.customerInEdit;
    }

    // Set the appropriate Customer property to the cell value entered.
    String newValue = e.Value as String;
    switch (this.dataGridView1.Columns[e.ColumnIndex].Name)
    {
        case "Company Name":
            customerTmp.CompanyName = newValue;
            break;

        case "Contact Name":
            customerTmp.ContactName = newValue;
            break;
    }
}

    Private Sub dataGridView1_CellValuePushed(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellValueEventArgs) _
    Handles dataGridView1.CellValuePushed

    Dim customerTmp As Customer = Nothing

    ' Store a reference to the Customer object for the row being edited.
    If e.RowIndex < Me.customers.Count Then

        ' If the user is editing a new row, create a new Customer object.
        If Me.customerInEdit Is Nothing Then
            Me.customerInEdit = New Customer( _
                CType(Me.customers(e.RowIndex), Customer).CompanyName, _
                CType(Me.customers(e.RowIndex), Customer).ContactName)
        End If
        customerTmp = Me.customerInEdit
        Me.rowInEdit = e.RowIndex

    Else
        customerTmp = Me.customerInEdit
    End If

    ' Set the appropriate Customer property to the cell value entered.
    Dim newValue As String = TryCast(e.Value, String)
    Select Case Me.dataGridView1.Columns(e.ColumnIndex).Name
        Case "Company Name"
            customerTmp.CompanyName = newValue
        Case "Contact Name"
            customerTmp.ContactName = newValue
    End Select

End Sub

  5. 为创建表示新创建的行的新 Customer 对象的 NewRowNeeded 事件实现处理程序。

    每当用户输入新记录的行时，就会发生此事件。

    void dataGridView1_NewRowNeeded( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewRowEventArgs^ /*e*/ )
{
   
   // Create a new Customer object when the user edits
   // the row for new records.
   this->customerInEdit = gcnew Customer;
   this->rowInEdit = this->dataGridView1->Rows->Count - 1;
}



    private void dataGridView1_NewRowNeeded(object sender,
    System.Windows.Forms.DataGridViewRowEventArgs e)
{
    // Create a new Customer object when the user edits
    // the row for new records.
    this.customerInEdit = new Customer();
    this.rowInEdit = this.dataGridView1.Rows.Count - 1;
}

    Private Sub dataGridView1_NewRowNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewRowEventArgs) _
    Handles dataGridView1.NewRowNeeded

    ' Create a new Customer object when the user edits
    ' the row for new records.
    Me.customerInEdit = New Customer()
    Me.rowInEdit = Me.dataGridView1.Rows.Count - 1

End Sub

  6. 为将新行或修改的行保存到数据存储的 RowValidated 事件实现处理程序。

    每当用户更改当前行时，就会发生此事件。

    void dataGridView1_RowValidated( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewCellEventArgs^ e )
{
   
   // Save row changes if any were made and release the edited 
   // Customer object if there is one.
   if ( e->RowIndex >= this->customers->Count && e->RowIndex != this->dataGridView1->Rows->Count - 1 )
   {
      
      // Add the new Customer object to the data store.
      this->customers->Add( this->customerInEdit );
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
   else
   if ( this->customerInEdit != nullptr && e->RowIndex < this->customers->Count )
   {
      
      // Save the modified Customer object in the data store.
      this->customers[ e->RowIndex ] = this->customerInEdit;
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
   else
   if ( this->dataGridView1->ContainsFocus )
   {
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
}



    private void dataGridView1_RowValidated(object sender,
    System.Windows.Forms.DataGridViewCellEventArgs e)
{
    // Save row changes if any were made and release the edited
    // Customer object if there is one.
    if (e.RowIndex >= this.customers.Count &&
        e.RowIndex != this.dataGridView1.Rows.Count - 1)
    {
        // Add the new Customer object to the data store.
        this.customers.Add(this.customerInEdit);
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
    else if (this.customerInEdit != null &&
        e.RowIndex < this.customers.Count)
    {
        // Save the modified Customer object in the data store.
        this.customers[e.RowIndex] = this.customerInEdit;
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
    else if (this.dataGridView1.ContainsFocus)
    {
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
}

    Private Sub dataGridView1_RowValidated(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) _
    Handles dataGridView1.RowValidated

    ' Save row changes if any were made and release the edited 
    ' Customer object if there is one.
    If e.RowIndex >= Me.customers.Count AndAlso _
        e.RowIndex <> Me.dataGridView1.Rows.Count - 1 Then

        ' Add the new Customer object to the data store.
        Me.customers.Add(Me.customerInEdit)
        Me.customerInEdit = Nothing
        Me.rowInEdit = -1

    ElseIf (Me.customerInEdit IsNot Nothing) AndAlso _
        e.RowIndex < Me.customers.Count Then

        ' Save the modified Customer object in the data store.
        Me.customers(e.RowIndex) = Me.customerInEdit
        Me.customerInEdit = Nothing
        Me.rowInEdit = -1

    ElseIf Me.dataGridView1.ContainsFocus Then

        Me.customerInEdit = Nothing
        Me.rowInEdit = -1

    End If

End Sub

  7. 为指示当用户在编辑模式下按两次或在非编辑模式下按一次 ESC 时是否发生 CancelRowEdit 事件的 RowDirtyStateNeeded 事件实现处理程序。

    默认情况下，除非在 RowDirtyStateNeeded 事件处理程序中将 QuestionEventArgs.Response 属性设置为 true，否则当当前行中的任何单元格被修改时，会在行反转时发生 CancelRowEdit。 当在运行时确定提交范围时，此事件很有用。

    void dataGridView1_RowDirtyStateNeeded( Object^ /*sender*/,
    System::Windows::Forms::QuestionEventArgs^ e )
{
   if (  !rowScopeCommit )
   {
      
      // In cell-level commit scope, indicate whether the value
      // of the current cell has been modified.
      e->Response = this->dataGridView1->IsCurrentCellDirty;
   }
}



    private void dataGridView1_RowDirtyStateNeeded(object sender,
    System.Windows.Forms.QuestionEventArgs e)
{
    if (!rowScopeCommit)
    {
        // In cell-level commit scope, indicate whether the value
        // of the current cell has been modified.
        e.Response = this.dataGridView1.IsCurrentCellDirty;
    }
}

    Private Sub dataGridView1_RowDirtyStateNeeded(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.QuestionEventArgs) _
    Handles dataGridView1.RowDirtyStateNeeded

    If Not rowScopeCommit Then

        ' In cell-level commit scope, indicate whether the value
        ' of the current cell has been modified.
        e.Response = Me.dataGridView1.IsCurrentCellDirty

    End If

End Sub

  8. 为丢弃表示当前行的 Customer 对象的值的 CancelRowEdit 事件实现处理程序。

    当用户在编辑模式下按两次或在非编辑模式下按一次 ESC 发出行反转信号时，将发生此事件。 如果当前行中没有任何单元格被修改，或者如果在 RowDirtyStateNeeded 事件处理程序中将 QuestionEventArgs.Response 属性的值设置为 false，则不会发生此事件。

    void dataGridView1_CancelRowEdit( Object^ /*sender*/,
    System::Windows::Forms::QuestionEventArgs^ /*e*/ )
{
   if ( this->rowInEdit == this->dataGridView1->Rows->Count - 2 &&
        this->rowInEdit == this->customers->Count )
   {
      
      // If the user has canceled the edit of a newly created row, 
      // replace the corresponding Customer object with a new, empty one.
      this->customerInEdit = gcnew Customer;
   }
   else
   {
      
      // If the user has canceled the edit of an existing row, 
      // release the corresponding Customer object.
      this->customerInEdit = nullptr;
      this->rowInEdit = -1;
   }
}



    private void dataGridView1_CancelRowEdit(object sender,
    System.Windows.Forms.QuestionEventArgs e)
{
    if (this.rowInEdit == this.dataGridView1.Rows.Count - 2 &&
        this.rowInEdit == this.customers.Count)
    {
        // If the user has canceled the edit of a newly created row,
        // replace the corresponding Customer object with a new, empty one.
        this.customerInEdit = new Customer();
    }
    else
    {
        // If the user has canceled the edit of an existing row,
        // release the corresponding Customer object.
        this.customerInEdit = null;
        this.rowInEdit = -1;
    }
}

    Private Sub dataGridView1_CancelRowEdit(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.QuestionEventArgs) _
    Handles dataGridView1.CancelRowEdit

    If Me.rowInEdit = Me.dataGridView1.Rows.Count - 2 AndAlso _
        Me.rowInEdit = Me.customers.Count Then

        ' If the user has canceled the edit of a newly created row, 
        ' replace the corresponding Customer object with a new, empty one.
        Me.customerInEdit = New Customer()

    Else

        ' If the user has canceled the edit of an existing row, 
        ' release the corresponding Customer object.
        Me.customerInEdit = Nothing
        Me.rowInEdit = -1

    End If

End Sub

  9. 为从数据存储中删除现有 Customer 对象或放弃表示新创建的行的未保存 Customer 对象的 UserDeletingRow 事件实现处理程序。

    每当用户通过单击行标题并按 Delete 键删除行时，就会发生此事件。

    void dataGridView1_UserDeletingRow( Object^ /*sender*/,
    System::Windows::Forms::DataGridViewRowCancelEventArgs^ e )
{
   if ( e->Row->Index < this->customers->Count )
   {
      
      // If the user has deleted an existing row, remove the 
      // corresponding Customer object from the data store.
      this->customers->RemoveAt( e->Row->Index );
   }

   if ( e->Row->Index == this->rowInEdit )
   {
      
      // If the user has deleted a newly created row, release
      // the corresponding Customer object. 
      this->rowInEdit = -1;
      this->customerInEdit = nullptr;
   }
}

    private void dataGridView1_UserDeletingRow(object sender,
    System.Windows.Forms.DataGridViewRowCancelEventArgs e)
{
    if (e.Row.Index < this.customers.Count)
    {
        // If the user has deleted an existing row, remove the
        // corresponding Customer object from the data store.
        this.customers.RemoveAt(e.Row.Index);
    }

    if (e.Row.Index == this.rowInEdit)
    {
        // If the user has deleted a newly created row, release
        // the corresponding Customer object.
        this.rowInEdit = -1;
        this.customerInEdit = null;
    }
}

    Private Sub dataGridView1_UserDeletingRow(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.DataGridViewRowCancelEventArgs) _
    Handles dataGridView1.UserDeletingRow

    If e.Row.Index < Me.customers.Count Then

        ' If the user has deleted an existing row, remove the 
        ' corresponding Customer object from the data store.
        Me.customers.RemoveAt(e.Row.Index)

    End If

    If e.Row.Index = Me.rowInEdit Then

        ' If the user has deleted a newly created row, release
        ' the corresponding Customer object. 
        Me.rowInEdit = -1
        Me.customerInEdit = Nothing

    End If

End Sub

  10. 实现简单的 Customers 类来表示此代码示例使用的数据项。

    public ref class Customer
{
private:
   String^ companyNameValue;
   String^ contactNameValue;

public:
   Customer()
   {
      
      // Leave fields empty.
   }

   Customer( String^ companyName, String^ contactName )
   {
      companyNameValue = companyName;
      contactNameValue = contactName;
   }


   property String^ CompanyName 
   {
      String^ get()
      {
         return companyNameValue;
      }

      void set( String^ value )
      {
         companyNameValue = value;
      }

   }

   property String^ ContactName 
   {
      String^ get()
      {
         return contactNameValue;
      }

      void set( String^ value )
      {
         contactNameValue = value;
      }

   }

};

    public class Customer
{
    private String companyNameValue;
    private String contactNameValue;

    public Customer()
    {
        // Leave fields empty.
    }

    public Customer(String companyName, String contactName)
    {
        companyNameValue = companyName;
        contactNameValue = contactName;
    }

    public String CompanyName
    {
        get
        {
            return companyNameValue;
        }
        set
        {
            companyNameValue = value;
        }
    }

    public String ContactName
    {
        get
        {
            return contactNameValue;
        }
        set
        {
            contactNameValue = value;
        }
    }
}

    Public Class Customer

    Private companyNameValue As String
    Private contactNameValue As String

    Public Sub New()
        ' Leave fields empty.
    End Sub

    Public Sub New(ByVal companyName As String, ByVal contactName As String)
        companyNameValue = companyName
        contactNameValue = contactName
    End Sub

    Public Property CompanyName() As String
        Get
            Return companyNameValue
        End Get
        Set(ByVal value As String)
            companyNameValue = value
        End Set
    End Property

    Public Property ContactName() As String
        Get
            Return contactNameValue
        End Get
        Set(ByVal value As String)
            contactNameValue = value
        End Set
    End Property

End Class

测试应用程序

现在可以测试窗体，以确保它的行为符合预期。

测试窗体

  • 编译并运行该应用程序。

    你将看到填充有三条客户记录的 DataGridView 控件。 你可以修改一行中多个单元格的值，然后在编辑模式下按两次或在非编辑模式下按一次 ESC 以将整行恢复为其原始值。 当你在控件中修改、添加或删除行时，数据存储中的 Customer 对象也会被修改、添加或删除。

后续步骤

此应用程序让你对在 DataGridView 控件中实现虚拟模式必须处理的事件有一个基本的了解。 你可以通过多种方式改进此基本应用程序：

  • 实现缓存来自外部数据库的值的数据存储。 缓存应根据需要检索和丢弃值，以便它仅包含需要显示的内容，同时消耗客户端计算机上的少量内存。

  • 根据要求微调数据存储的性能。 例如，你可能希望通过使用更大的缓存大小和最小化数据库查询的数量来补偿网络连接缓慢问题而不是客户端计算机的内存限制。

有关从外部数据库缓存值的更多信息，请参阅如何：在 Windows 窗体 DataGridView 控件中实现实时数据加载的虚拟模式。

另请参阅