如何：存取 Windows Form DataGridViewComboBoxCell 下拉式清單中的物件

如同 ComboBox 控制項，DataGridViewComboBoxColumn 和 DataGridViewComboBoxCell 類型可讓您將任意物件新增至其下拉式清單。 透過這項功能，您可以在下拉式清單中代表複雜的狀態，而不需要將對應的物件儲存在個別的集合中。

不同於 ComboBox 控制項，DataGridView 類型沒有擷取目前選取物件的 SelectedItem 屬性。 相反地，您必須將 DataGridViewComboBoxColumn.ValueMember 或 DataGridViewComboBoxCell.ValueMember 屬性設定為商業物件上的屬性名稱。 當使用者進行選取時，商業物件的指示屬性會設定儲存格 Value 屬性。

若要透過儲存格值擷取商業物件，ValueMember 屬性必須指出傳回商業物件本身參考的屬性。 因此，如果商業物件的類型不在您的控制之下，您必須透過繼承擴充類型來新增這類屬性。

下列程式示範如何使用商業物件填入下拉式清單，並透過儲存格 Value 屬性擷取物件。

將商業物件新增至下拉式清單

1. 建立新的 DataGridViewComboBoxColumn，並填入其 Items 集合。 或者，您可以將資料行 DataSource 屬性設定為商業物件的集合。 不過，在此案例下，您無法在集合中建立對應的商業物件，將「未指派」新增至下拉式清單。

   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. 設定 DisplayMember 和 ValueMember 屬性。 DisplayMember 會指出要顯示在下拉式清單中之商業物件的屬性。 ValueMember 指出傳回商業物件參考的屬性。

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

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

3. 請確定您的商務物件類型包含傳回目前實例參考的屬性。 這個屬性必須以上一個步驟中指派給 ValueMember 的值命名。

   public Employee Self
   {
       get { return this; }
   }
   

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

擷取目前選取的商業物件

• 取得儲存格 Value 屬性，並將其轉換成商業物件類型。

  // 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)
  

範例

完整範例示範在下拉式清單中使用商業物件。 在此範例中，DataGridView 控制項會繫結至 Task 物件的集合。 每個 Task 物件都有一個 AssignedTo 屬性，指出目前指派給該工作的 Employee 物件。 Assigned To 資料行會顯示每個指派員工 Name 屬性值，如果 Task.AssignedTo 屬性值為 null，則為「未指派」。

若要檢視此範例的行為，請執行下列步驟：

1. 從下拉式清單中選取不同的值，或在下拉式方塊中按 CTRL+0，以變更 Assigned To 資料行中的指派。

2. 按一下 [Generate Report]，以顯示目前的指派。 這示範 Assigned To 資料行中的變更會自動更新 tasks 集合。

3. 按一下 [Request Status] 按鈕，針對該資料列呼叫目前 Employee 物件的 RequestStatus 方法。 這示範已成功擷取選取的物件。

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

正在編譯程式碼

這個範例需要：

• 本系統和 System.Windows.Forms 組件的參考。

另請參閱

• DataGridView
• DataGridViewComboBoxColumn
• DataGridViewComboBoxColumn.Items
• DataGridViewComboBoxColumn.DataSource
• DataGridViewComboBoxColumn.ValueMember
• DataGridViewComboBoxCell
• DataGridViewComboBoxCell.Items
• DataGridViewComboBoxCell.DataSource
• DataGridViewComboBoxCell.ValueMember
• DataGridViewCell.Value
• ComboBox
• 在 Windows Forms DataGridView 控制項中顯示資料