Como acessar objetos de acesso em uma lista suspensa DataGridViewComboBoxCell dos Windows Forms

Como o ComboBox controle, os DataGridViewComboBoxColumn tipos e DataGridViewComboBoxCell permitem que você adicione objetos arbitrários às suas listas suspensas. Com esse recurso, você pode representar estados complexos em uma lista suspensa sem a necessidade de armazenar objetos correspondentes em uma coleção separada.

Ao contrário do ComboBox controle, os DataGridView tipos não têm uma SelectedItem propriedade para recuperar o objeto selecionado no momento. Em vez disso, você deve definir a DataGridViewComboBoxColumn.ValueMember propriedade ou DataGridViewComboBoxCell.ValueMember para o nome de uma propriedade em seu objeto comercial. Quando o usuário faz uma seleção, a propriedade indicada do objeto comercial define a propriedade cell Value .

Para recuperar o objeto comercial por meio do valor de célula, a propriedade ValueMember deve indicar uma propriedade que retorne uma referência ao objeto comercial em si. Portanto, se o tipo de objeto comercial não estiver sob seu controle, você deverá adicionar essa propriedade estendendo o tipo por meio de herança.

Os procedimentos a seguir demonstram como preencher uma lista suspensa com objetos comerciais e recuperar os objetos por meio da propriedade cell Value .

Para adicionar objetos comerciais à lista suspensa

1. Crie um novo DataGridViewComboBoxColumn e preencha sua Items coleção. Como alternativa, você pode definir a propriedade column DataSource para a coleção de objetos comerciais. Nesse caso, no entanto, você não pode adicionar "não atribuído" à lista suspensa sem criar um objeto comercial correspondente em sua coleção.

   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. Definir as propriedades DisplayMember e ValueMember. DisplayMember Indica a propriedade do objeto comercial a ser exibido na lista suspensa. ValueMember Indica a propriedade que retorna uma referência ao objeto comercial.

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

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

3. Certifique-se de que o tipo de objeto de negócios contenha uma propriedade que retorne uma referência à instância atual. Essa propriedade deve ser nomeada com o valor atribuído na ValueMember etapa anterior.

   public Employee Self
   {
       get { return this; }
   }
   

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

Para recuperar o objeto comercial selecionado no momento

• Obtenha a propriedade cell Value e converta-a no tipo de objeto comercial.

  // 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)
  

Exemplo

O exemplo completo demonstra o uso de objetos de negócios em uma lista suspensa. No exemplo, um DataGridView controle é vinculado a uma coleção de Task objetos. Cada objeto Task tem uma propriedade AssignedTo que indica o objeto Employee atualmente atribuído à tarefa. A coluna Assigned To exibe o de valor da propriedade Name para cada funcionário atribuído ou "não atribuído", se o valor da propriedade Task.AssignedTo for null.

Para exibir o comportamento deste exemplo, execute as seguintes etapas:

1. Altere as atribuições na coluna Assigned To selecionando valores diferentes nas listas suspensas ou pressionando CTRL+0 em uma célula de caixa de combinação.

2. Clique em Generate Report para exibir as atribuições atuais. Isso demonstra que uma alteração à coluna Assigned To atualiza automaticamente a coleção tasks.

3. Clique em um botão Request Status para chamar o método RequestStatus do objeto Employee atual para aquela linha. Isso demonstra que o objeto selecionado foi recuperado com êxito.

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

Compilando o código

Este exemplo requer:

• Referências aos assemblies Sistema e System.Windows.Forms.

Confira também

• DataGridView
• DataGridViewComboBoxColumn
• DataGridViewComboBoxColumn.Items
• DataGridViewComboBoxColumn.DataSource
• DataGridViewComboBoxColumn.ValueMember
• DataGridViewComboBoxCell
• DataGridViewComboBoxCell.Items
• DataGridViewComboBoxCell.DataSource
• DataGridViewComboBoxCell.ValueMember
• DataGridViewCell.Value
• ComboBox
• Exibindo dados no controle DataGridView do Windows Forms