Como: Objetos de acesso em uma lista de suspensa DataGridViewComboBoxCell Windows Forms

Artigo
08/25/2010

Como a ComboBox controle, o DataGridViewComboBoxColumn e DataGridViewComboBoxCell tipos 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 os objetos correspondentes em uma coleção separada.

Ao contrário de ComboBox controle, o DataGridView tipos não têm um SelectedItem propriedade para recuperar o objeto selecionado no momento. Em vez disso, você deve conjunto o DataGridViewComboBoxColumn.ValueMember ou DataGridViewComboBoxCell.ValueMember propriedade para o nome de uma propriedade no objeto de negócios. Quando o usuário fizer uma seleção, a propriedade indicada do objeto comercial define a célula Value propriedade.

Para recuperar o objeto de negócios por meio do valor da célula, a ValueMember propriedade deve indicar uma propriedade que retorna uma referência para o objeto de negócios. Portanto, se o tipo de objeto comercial não estiver sob seu controle, você deve adicionar essa propriedade Estendendo tipo por meio de herança.

Os procedimentos a seguir demonstram como popular uma lista suspensa com objetos de negócios e recuperar os objetos por meio da célula Value propriedade.

Para adicionar objetos comerciais para o lista suspensa

Criar um novo DataGridViewComboBoxColumn e popular seu Items coleção. Como alternativa, você pode conjunto a coluna DataSource propriedade à coleção de objetos de negócios. Nesse caso, entretanto, você não pode adicionar "não atribuídos" à lista suspensa sem criar um objeto de negócios correspondente na sua coleção.

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"

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";

Definir as propriedades DisplayMember e ValueMember.DisplayMember indica a propriedade do objeto comercial para exibir na lista suspensa. ValueMember indica a propriedade que retorna uma referência para o objeto de negócios.
```
assignedToColumn.DisplayMember = "Name"
assignedToColumn.ValueMember = "Self"
```
```
assignedToColumn.DisplayMember = "Name";
assignedToColumn.ValueMember = "Self";
```
Certifique-se de que seu tipo de objeto de negócios contém uma propriedade que retorna uma referência à instância corrente.Esta propriedade deve ser nomeada com o valor atribuído a ValueMember na etapa anterior.
```
Public ReadOnly Property Self() As Employee
    Get
        Return Me
    End Get
End Property
```
```
public Employee Self 
{ 
    get { return this; } 
}
```

Para recuperar o objeto de negócios selecionado no momento

Obtenha a célula Value propriedade e converta-a para o tipo de objeto de negócios.

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

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

Exemplo

O exemplo completo demonstra o uso de objetos de negócios em uma lista drop-down.No exemplo, um DataGridView controle está limite a uma coleção de Task objetos. Cada Task o objeto tem um AssignedTo propriedade que indica a Employee objeto atribuído atualmente a essa tarefa. The Assigned To coluna exibe o Namevalor da propriedade para cada um atribuído funcionário ou "não atribuído" se o Task.AssignedTo valor da propriedade é null.

Para exibir o comportamento de neste exemplo, execute as seguintes etapas:

Alterar as atribuições no Assigned To coluna selecionando valores diferentes nas listas suspensas ou pressione CTRL + 0 em uma célula da caixa de combinação.
clicar Generate Report Para exibir as atribuições corrente. Isso demonstra que uma alterar no Assigned To coluna atualiza automaticamente o tasks coleção.
clicar um Request Status botão para chamar a RequestStatus método do corrente Employee objeto para aquela linha. Isso demonstra que o objeto selecionado foi recuperado com êxito.

Imports System
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

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");
    }
}