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Cómo: Obtener acceso a objetos en una DataGridViewComboBoxCell de lista de formularios de Windows Forms Drop-Down

Al igual que el ComboBox control , los DataGridViewComboBoxColumn tipos y DataGridViewComboBoxCell permiten agregar objetos arbitrarios a sus listas desplegables. Con esta característica, puede representar estados complejos en una lista desplegable sin tener que almacenar los objetos correspondientes en una colección independiente.

A diferencia del ComboBox control , los DataGridView tipos no tienen una SelectedItem propiedad para recuperar el objeto seleccionado actualmente. En su lugar, debe establecer la propiedad DataGridViewComboBoxColumn.ValueMember o DataGridViewComboBoxCell.ValueMember al nombre de una propiedad de su objeto de negocio. Cuando el usuario realiza una selección, la propiedad indicada del objeto de negocio establece la propiedad Value de la celda.

Para recuperar el objeto de negocio a través del valor de celda, la ValueMember propiedad debe indicar una propiedad que devuelva una referencia al propio objeto de negocio. Por lo tanto, si el tipo del objeto de negocio no está bajo su control, debe agregar dicha propiedad extendiendo el tipo a través de la herencia.

Los procedimientos siguientes muestran cómo rellenar una lista desplegable con objetos empresariales y recuperar los objetos a través de la propiedad cell Value .

Para agregar objetos empresariales a la lista desplegable

  1. Cree un nuevo DataGridViewComboBoxColumn y rellene su Items colección. Como alternativa, puede establecer la propiedad column DataSource en la colección de objetos de negocio. Sin embargo, en ese caso, no puedes agregar "sin asignar" a la lista desplegable sin antes crear un objeto empresarial correspondiente en tu colección.

    DataGridViewComboBoxColumn assignedToColumn =
    new DataGridViewComboBoxColumn();

// Populate the combo box drop-down list with Employee objects.
foreach (Employee e in employees) assignedToColumn.Items.Add(e);

// Add "unassigned" to the drop-down list and display it for
// empty AssignedTo values or when the user presses CTRL+0.
assignedToColumn.Items.Add("unassigned");
assignedToColumn.DefaultCellStyle.NullValue = "unassigned";

    Dim assignedToColumn As New DataGridViewComboBoxColumn()

' Populate the combo box drop-down list with Employee objects. 
For Each e As Employee In employees
    assignedToColumn.Items.Add(e)
Next

' Add "unassigned" to the drop-down list and display it for 
' empty AssignedTo values or when the user presses CTRL+0. 
assignedToColumn.Items.Add("unassigned")
assignedToColumn.DefaultCellStyle.NullValue = "unassigned"

  2. Establezca las propiedades DisplayMember y ValueMember. DisplayMember indica la propiedad del objeto de negocio que se va a mostrar en la lista desplegable. ValueMember indica la propiedad que devuelve una referencia al objeto de negocio.

    assignedToColumn.DisplayMember = "Name";
assignedToColumn.ValueMember = "Self";

    assignedToColumn.DisplayMember = "Name"
assignedToColumn.ValueMember = "Self"

  3. Asegúrese de que el tipo de objeto de negocio contiene una propiedad que devuelve una referencia a la instancia actual. Esta propiedad debe denominarse con el valor asignado a ValueMember en el paso anterior.

    public Employee Self
{
    get { return this; }
}

    Public ReadOnly Property Self() As Employee
    Get
        Return Me
    End Get
End Property

Para recuperar el objeto de negocio seleccionado actualmente

  • Obtiene la propiedad cell Value y la convierte en el tipo de objeto de negocio.

    // Retrieve the Employee object from the "Assigned To" cell.
Employee assignedTo = dataGridView1.Rows[e.RowIndex]
    .Cells["Assigned To"].Value as Employee;

    ' Retrieve the Employee object from the "Assigned To" cell.
Dim assignedTo As Employee = TryCast(dataGridView1.Rows(e.RowIndex) _
    .Cells("Assigned To").Value, Employee)

Ejemplo

En el ejemplo completo se muestra el uso de objetos empresariales en una lista desplegable. En el ejemplo, un DataGridView control está enlazado a una colección de Task objetos . Cada Task objeto tiene una AssignedTo propiedad que indica el Employee objeto asignado actualmente a esa tarea. La Assigned To columna muestra el valor de la propiedad Name de cada empleado asignado, o "sin asignar" si el valor de la propiedad Task.AssignedTo es null.

Para ver el comportamiento de este ejemplo, realice los pasos siguientes:

  1. Cambie las asignaciones de la Assigned To columna seleccionando valores diferentes en las listas desplegables o presionando CTRL+0 en una celda de cuadro combinado.

  2. Haga clic Generate Report para mostrar las asignaciones actuales. Esto muestra que un cambio en la Assigned To columna actualiza automáticamente la tasks colección.

  3. Haga clic en el botón Request Status para llamar al método RequestStatus del objeto actual Employee de la fila. Esto muestra que el objeto seleccionado se ha recuperado correctamente.

using System;
using System.Text;
using System.Collections.Generic;
using System.Windows.Forms;

public class Form1 : Form
{
    private List<Employee> employees = new List<Employee>();
    private List<Task> tasks = new List<Task>();
    private Button reportButton = new Button();
    private DataGridView dataGridView1 = new DataGridView();

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

    public Form1()
    {
        dataGridView1.Dock = DockStyle.Fill;
        dataGridView1.AutoSizeColumnsMode =
            DataGridViewAutoSizeColumnsMode.AllCells;
        reportButton.Text = "Generate Report";
        reportButton.Dock = DockStyle.Top;
        reportButton.Click += new EventHandler(reportButton_Click);

        Controls.Add(dataGridView1);
        Controls.Add(reportButton);
        Load += new EventHandler(Form1_Load);
        Text = "DataGridViewComboBoxColumn Demo";
    }

    // Initializes the data source and populates the DataGridView control.
    private void Form1_Load(object sender, EventArgs e)
    {
        PopulateLists();
        dataGridView1.AutoGenerateColumns = false;
        dataGridView1.DataSource = tasks;
        AddColumns();
    }

    // Populates the employees and tasks lists.
    private void PopulateLists()
    {
        employees.Add(new Employee("Harry"));
        employees.Add(new Employee("Sally"));
        employees.Add(new Employee("Roy"));
        employees.Add(new Employee("Pris"));
        tasks.Add(new Task(1, employees[1]));
        tasks.Add(new Task(2));
        tasks.Add(new Task(3, employees[2]));
        tasks.Add(new Task(4));
    }

    // Configures columns for the DataGridView control.
    private void AddColumns()
    {
        DataGridViewTextBoxColumn idColumn =
            new DataGridViewTextBoxColumn();
        idColumn.Name = "Task";
        idColumn.DataPropertyName = "Id";
        idColumn.ReadOnly = true;

        DataGridViewComboBoxColumn assignedToColumn =
            new DataGridViewComboBoxColumn();

        // Populate the combo box drop-down list with Employee objects.
        foreach (Employee e in employees) assignedToColumn.Items.Add(e);

        // Add "unassigned" to the drop-down list and display it for
        // empty AssignedTo values or when the user presses CTRL+0.
        assignedToColumn.Items.Add("unassigned");
        assignedToColumn.DefaultCellStyle.NullValue = "unassigned";

        assignedToColumn.Name = "Assigned To";
        assignedToColumn.DataPropertyName = "AssignedTo";
        assignedToColumn.AutoComplete = true;
        assignedToColumn.DisplayMember = "Name";
        assignedToColumn.ValueMember = "Self";

        // Add a button column.
        DataGridViewButtonColumn buttonColumn =
            new DataGridViewButtonColumn();
        buttonColumn.HeaderText = "";
        buttonColumn.Name = "Status Request";
        buttonColumn.Text = "Request Status";
        buttonColumn.UseColumnTextForButtonValue = true;

        dataGridView1.Columns.Add(idColumn);
        dataGridView1.Columns.Add(assignedToColumn);
        dataGridView1.Columns.Add(buttonColumn);

        // Add a CellClick handler to handle clicks in the button column.
        dataGridView1.CellClick +=
            new DataGridViewCellEventHandler(dataGridView1_CellClick);
    }

    // Reports on task assignments.
    private void reportButton_Click(object sender, EventArgs e)
    {
        StringBuilder report = new StringBuilder();
        foreach (Task t in tasks)
        {
            String assignment =
                t.AssignedTo == null ?
                "unassigned" : "assigned to " + t.AssignedTo.Name;
            report.AppendFormat("Task {0} is {1}.", t.Id, assignment);
            report.Append(Environment.NewLine);
        }
        MessageBox.Show(report.ToString(), "Task Assignments");
    }

    // Calls the Employee.RequestStatus method.
    void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
    {
        // Ignore clicks that are not on button cells.
        if (e.RowIndex < 0 || e.ColumnIndex !=
            dataGridView1.Columns["Status Request"].Index) return;

        // Retrieve the task ID.
        Int32 taskID = (Int32)dataGridView1[0, e.RowIndex].Value;

        // Retrieve the Employee object from the "Assigned To" cell.
        Employee assignedTo = dataGridView1.Rows[e.RowIndex]
            .Cells["Assigned To"].Value as Employee;

        // Request status through the Employee object if present.
        if (assignedTo != null)
        {
            assignedTo.RequestStatus(taskID);
        }
        else
        {
            MessageBox.Show(String.Format(
                "Task {0} is unassigned.", taskID), "Status Request");
        }
    }
}

public class Task
{
    public Task(Int32 id)
    {
        idValue = id;
    }

    public Task(Int32 id, Employee assignedTo)
    {
        idValue = id;
        assignedToValue = assignedTo;
    }

    private Int32 idValue;
    public Int32 Id
    {
        get { return idValue; }
        set { idValue = value; }
    }

    private Employee assignedToValue;
    public Employee AssignedTo
    {
        get { return assignedToValue; }
        set { assignedToValue = value; }
    }
}

public class Employee
{
    public Employee(String name)
    {
        nameValue = name;
    }

    private String nameValue;
    public String Name
    {
        get { return nameValue; }
        set { nameValue = value; }
    }

    public Employee Self
    {
        get { return this; }
    }

    public void RequestStatus(Int32 taskID)
    {
        MessageBox.Show(String.Format(
            "Status for task {0} has been requested from {1}.",
            taskID, nameValue), "Status Request");
    }
}

Imports System.Text
Imports System.Collections.Generic
Imports System.Windows.Forms

Public Class Form1
    Inherits Form

    Private employees As New List(Of Employee)
    Private tasks As New List(Of Task)
    Private WithEvents reportButton As New Button
    Private WithEvents dataGridView1 As New DataGridView

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

    Sub New()
        dataGridView1.Dock = DockStyle.Fill
        dataGridView1.AutoSizeColumnsMode = _
            DataGridViewAutoSizeColumnsMode.AllCells
        reportButton.Text = "Generate Report"
        reportButton.Dock = DockStyle.Top

        Controls.Add(dataGridView1)
        Controls.Add(reportButton)
        Text = "DataGridViewComboBoxColumn Demo"
    End Sub

    ' Initializes the data source and populates the DataGridView control.
    Private Sub Form1_Load(ByVal sender As Object, _
        ByVal e As EventArgs) Handles Me.Load

        PopulateLists()
        dataGridView1.AutoGenerateColumns = False
        dataGridView1.DataSource = tasks
        AddColumns()

    End Sub

    ' Populates the employees and tasks lists. 
    Private Sub PopulateLists()
        employees.Add(New Employee("Harry"))
        employees.Add(New Employee("Sally"))
        employees.Add(New Employee("Roy"))
        employees.Add(New Employee("Pris"))
        tasks.Add(New Task(1, employees(1)))
        tasks.Add(New Task(2))
        tasks.Add(New Task(3, employees(2)))
        tasks.Add(New Task(4))
    End Sub

    ' Configures columns for the DataGridView control.
    Private Sub AddColumns()

        Dim idColumn As New DataGridViewTextBoxColumn()
        idColumn.Name = "Task"
        idColumn.DataPropertyName = "Id"
        idColumn.ReadOnly = True

        Dim assignedToColumn As New DataGridViewComboBoxColumn()

        ' Populate the combo box drop-down list with Employee objects. 
        For Each e As Employee In employees
            assignedToColumn.Items.Add(e)
        Next

        ' Add "unassigned" to the drop-down list and display it for 
        ' empty AssignedTo values or when the user presses CTRL+0. 
        assignedToColumn.Items.Add("unassigned")
        assignedToColumn.DefaultCellStyle.NullValue = "unassigned"

        assignedToColumn.Name = "Assigned To"
        assignedToColumn.DataPropertyName = "AssignedTo"
        assignedToColumn.AutoComplete = True
        assignedToColumn.DisplayMember = "Name"
        assignedToColumn.ValueMember = "Self"

        ' Add a button column. 
        Dim buttonColumn As New DataGridViewButtonColumn()
        buttonColumn.HeaderText = ""
        buttonColumn.Name = "Status Request"
        buttonColumn.Text = "Request Status"
        buttonColumn.UseColumnTextForButtonValue = True

        dataGridView1.Columns.Add(idColumn)
        dataGridView1.Columns.Add(assignedToColumn)
        dataGridView1.Columns.Add(buttonColumn)

    End Sub

    ' Reports on task assignments. 
    Private Sub reportButton_Click(ByVal sender As Object, _
        ByVal e As EventArgs) Handles reportButton.Click

        Dim report As New StringBuilder()
        For Each t As Task In tasks
            Dim assignment As String
            If t.AssignedTo Is Nothing Then
                assignment = "unassigned"
            Else
                assignment = "assigned to " + t.AssignedTo.Name
            End If
            report.AppendFormat("Task {0} is {1}.", t.Id, assignment)
            report.Append(Environment.NewLine)
        Next
        MessageBox.Show(report.ToString(), "Task Assignments")

    End Sub

    ' Calls the Employee.RequestStatus method.
    Private Sub dataGridView1_CellClick(ByVal sender As Object, _
        ByVal e As DataGridViewCellEventArgs) _
        Handles dataGridView1.CellClick

        ' Ignore clicks that are not on button cells. 
        If e.RowIndex < 0 OrElse Not e.ColumnIndex = _
            dataGridView1.Columns("Status Request").Index Then Return

        ' Retrieve the task ID.
        Dim taskID As Int32 = CInt(dataGridView1(0, e.RowIndex).Value)

        ' Retrieve the Employee object from the "Assigned To" cell.
        Dim assignedTo As Employee = TryCast(dataGridView1.Rows(e.RowIndex) _
            .Cells("Assigned To").Value, Employee)

        ' Request status through the Employee object if present. 
        If assignedTo IsNot Nothing Then
            assignedTo.RequestStatus(taskID)
        Else
            MessageBox.Show(String.Format( _
                "Task {0} is unassigned.", taskID), "Status Request")
        End If

    End Sub

End Class

Public Class Task

    Sub New(ByVal id As Int32)
        idValue = id
    End Sub

    Sub New(ByVal id As Int32, ByVal assignedTo As Employee)
        idValue = id
        assignedToValue = assignedTo
    End Sub

    Private idValue As Int32
    Public Property Id() As Int32
        Get
            Return idValue
        End Get
        Set(ByVal value As Int32)
            idValue = value
        End Set
    End Property

    Private assignedToValue As Employee
    Public Property AssignedTo() As Employee
        Get
            Return assignedToValue
        End Get
        Set(ByVal value As Employee)
            assignedToValue = value
        End Set
    End Property

End Class

Public Class Employee

    Sub New(ByVal name As String)
        nameValue = name
    End Sub

    Private nameValue As String
    Public Property Name() As String
        Get
            Return nameValue
        End Get
        Set(ByVal value As String)
            nameValue = value
        End Set
    End Property

    Public ReadOnly Property Self() As Employee
        Get
            Return Me
        End Get
    End Property

    Public Sub RequestStatus(ByVal taskID As Int32)
        MessageBox.Show(String.Format( _
            "Status for task {0} has been requested from {1}.", _
            taskID, nameValue), "Status Request")
    End Sub

End Class

Compilar el código

Este ejemplo requiere:

  • Referencias a los ensamblados System y System.Windows.Forms.

Consulte también