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Exemplarische Vorgehensweise: Implementieren des virtuellen Modus im DataGridView-Steuerelement in Windows Forms

Wenn Sie sehr große Mengen von Tabellendaten in einem DataGridView-Steuerelement anzeigen möchten, können Sie die VirtualMode-Eigenschaft auf true setzen und die Interaktion des Steuerelements mit seinem Datenspeicher explizit verwalten. Dadurch können Sie die Leistung des Steuerelements in dieser Situation optimieren.

Das DataGridView-Steuerelement bietet mehrere Ereignisse, mit denen Sie mit einem benutzerdefinierten Datenspeicher interagieren können. Diese exemplarische Vorgehensweise führt Sie durch den Prozess der Implementierung dieser Ereignishandler. Das Codebeispiel in diesem Thema verwendet zur Veranschaulichung eine sehr einfache Datenquelle. In einer Produktionsumgebung laden Sie in der Regel nur die Zeilen, die Sie in einem Cache anzeigen müssen, und behandeln DataGridView-Ereignisse, mit denen sie interagieren und den Cache aktualisieren können. Weitere Informationen finden Sie unter Implementieren des virtuellen Modus mit Just-In-Time-Laden von Daten in das DataGridView-Steuerelement in Windows Forms.

Informationen zum Kopieren des Codes in diesem Thema als einzelner Eintrag finden Sie unter Gewusst wie: Implementieren des virtuellen Modus in das DataGridView-Steuerelement in Windows Forms.

Erstellen des Formulars

So implementieren Sie den virtuellen Modus:

  1. Erstellen Sie eine Klasse, die von Form abgeleitet ist und ein DataGridView-Steuerelement enthält.

    Der folgende Code enthält einige einfache Initialisierungen. Er deklariert einige Variablen, die in späteren Schritten verwendet werden, stellt eine Main-Methode bereit und stellt ein einfaches Formularlayout im Klassenkonstruktor bereit.

    #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. Implementieren Sie einen Handler für das Load-Ereignis Ihres Formulars, das das DataGridView-Steuerelement initialisiert und den Datenspeicher mit Beispielwerten auffüllt.

    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. Implementieren Sie einen Handler für das CellValueNeeded-Ereignis, das den angeforderten Zellwert aus dem Datenspeicher oder das aktuell bearbeitete Customer-Objekt abruft.

    Dieses Ereignis tritt immer dann auf, wenn das DataGridView-Steuerelement eine Zelle zeichnen muss.

    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. Implementieren Sie einen Handler für das CellValuePushed-Ereignis, das einen bearbeiteten Zellwert im Customer-Objekt speichert, das die bearbeitete Zeile darstellt. Dieses Ereignis tritt immer dann auf, wenn der Benutzer eine Zellwertänderung committet.

    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. Implementieren Sie einen Handler für das NewRowNeeded-Ereignis, das ein neues Customer-Objekt erstellt, das eine neu erstellte Zeile darstellt.

    Dieses Ereignis tritt immer dann auf, wenn der Benutzer die Zeile für neue Datensätze eingibt.

    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. Implementieren Sie einen Handler für das RowValidated-Ereignis, das neue oder geänderte Zeilen im Datenspeicher speichert.

    Dieses Ereignis tritt immer dann auf, wenn der Benutzer die aktuelle Zeile ändert.

    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. Implementieren Sie einen Handler für das RowDirtyStateNeeded-Ereignis, der angibt, ob das CancelRowEdit-Ereignis eintritt, wenn der Benutzer die Zeilenwiederherstellung durch zweimaliges Drücken von ESC im Bearbeitungsmodus oder einmaliges Drücken außerhalb des Bearbeitungsmodus signalisiert.

    Standardmäßig tritt CancelRowEdit bei der Zeilenwiederherstellung auf, wenn Zellen in der aktuellen Zeile geändert wurden, es sei denn, die QuestionEventArgs.Response-Eigenschaft wird im RowDirtyStateNeeded-Ereignishandler auf true gesetzt. Dieses Ereignis ist nützlich, wenn der Commitbereich zur Laufzeit bestimmt wird.

    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. Implementieren Sie einen Handler für das CancelRowEdit-Ereignis, das die Werte des Customer-Objekts verwirft, das die aktuelle Zeile darstellt.

    Dieses Ereignis tritt ein, wenn der Benutzer die Zeilenwiederherstellung durch zweimaliges Drücken von ESC im Bearbeitungsmodus oder einmaliges Drücken außerhalb des Bearbeitungsmodus signalisiert. Dieses Ereignis tritt nicht ein, wenn keine Zellen in der aktuellen Zeile geändert wurden oder wenn der Wert der QuestionEventArgs.Response-Eigenschaft in einem RowDirtyStateNeeded-Ereignishandler auf false gesetzt wurde.

    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. Implementieren Sie einen Handler für das UserDeletingRow-Ereignis, der ein vorhandenes Customer-Objekt aus dem Datenspeicher löscht oder ein nicht gespeichertes Customer-Objekt, das eine neu erstellte Zeile darstellt, verwirft.

    Dieses Ereignis tritt immer dann auf, wenn der Benutzer eine Zeile löscht, indem er auf eine Zeilenüberschrift klickt und die DELETE-Taste drückt.

    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. Implementieren Sie eine einfache Customers-Klasse, um die Datenelemente darzustellen, die von diesem Codebeispiel verwendet werden.

    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
    

Testen der Anwendung

Sie können das Formular jetzt testen, um sicherzustellen, dass das Verhalten wie erwartet ausfällt.

So testen Sie das Formular

  • Kompilieren Sie die Anwendung, und führen Sie sie aus.

    Sie sehen ein DataGridView-Steuerelement, das mit drei Kundendatensätzen gefüllt ist. Sie können die Werte mehrerer Zellen in einer Zeile ändern und ESC im Bearbeitungsmodus zweimal und außerhalb des Bearbeitungsmodus einmal drücken, um die gesamte Zeile mit ihren ursprünglichen Werten wiederherzustellen. Wenn Sie Zeilen im Steuerelement ändern, hinzufügen oder löschen, werden Customer-Objekte im Datenspeicher ebenfalls geändert, hinzugefügt oder gelöscht.

Nächste Schritte

Diese Anwendung bietet Ihnen ein grundlegendes Verständnis der Ereignisse, die Sie behandeln müssen, um den virtuellen Modus im DataGridView-Steuerelement zu implementieren. Sie können diese einfache Anwendung auf verschiedene Arten verbessern:

  • Implementieren Sie einen Datenspeicher, der Werte aus einer externen Datenbank zwischenspeichert. Der Cache sollte bei Bedarf Werte abrufen und verwerfen, so dass er nur das enthält, was für die Anzeige erforderlich ist, und dabei nur wenig Speicherplatz auf dem Client-Computer beansprucht.

  • Optimieren Sie die Leistung des Datenspeichers je nach Ihren Anforderungen. So könnten Sie beispielsweise langsame Netzwerkverbindungen eher durch einen größeren Cache und eine geringere Anzahl von Datenbankabfragen kompensieren als durch Speicherbeschränkungen auf dem Client-Computer.

Weitere Informationen zum Zwischenspeichern von Werten aus einer externen Datenbank finden Sie unter Gewusst wie: Implementieren des virtuellen Modus mit Just-In-Time-Laden von Daten in das DataGridView-Steuerelement in Windows Forms.

Weitere Informationen