Я реализовал код для datagridview в virtualmode. Мой магазин содержит 42 товара в array. Может кто-нибудь объяснить мне, почему сначала он вызывает CellValueNeeded 42 раза, а затем 13 раз? Я понимаю 13 раз, потому что это предметы, которые можно показывать на сетке в режиме реального времени, но я не понимаю, что 42 раза раньше. Если бы у меня было миллион элементов в массиве CellValueNeeded, его также первоначально назвали бы миллионами раз, что не имеет смысла для меня, поскольку эти записи не требуются в этот момент, а 13, и, с моей точки зрения, это не то, для чего предназначен виртуальный режим.
Код был взят из ссылки MSDN
Полный код:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace DataGridViewVirtual
{
public partial class Form1 : Form
{
// 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;
public Form1()
{
InitializeComponent();
this.dataGridView1.Dock = DockStyle.None;
this.Controls.Add(this.dataGridView1);
this.Load += new EventHandler(Form1_Load);
this.Text = "DataGridView virtual-mode demo (row-level commit scope)";
}
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.AllCells;
// Add some sample entries to the data store.
this.customers.Add(new Customer(
"1", "1"));
this.customers.Add(new Customer(
"2", "2"));
this.customers.Add(new Customer(
"3", "3"));
this.customers.Add(new Customer(
"4", "4"));
this.customers.Add(new Customer(
"5", "5"));
this.customers.Add(new Customer(
"6", "6"));
this.customers.Add(new Customer(
"7", "7"));
this.customers.Add(new Customer(
"8", "8"));
this.customers.Add(new Customer(
"9", "9"));
this.customers.Add(new Customer(
"10", "10"));
this.customers.Add(new Customer(
"11", "11"));
this.customers.Add(new Customer(
"12", "12"));
this.customers.Add(new Customer(
"13", "13"));
this.customers.Add(new Customer(
"14", "14"));
this.customers.Add(new Customer(
"15", "15"));
this.customers.Add(new Customer(
"16", "16"));
this.customers.Add(new Customer(
"17", "17"));
this.customers.Add(new Customer(
"18", "18"));
this.customers.Add(new Customer(
"19", "19"));
this.customers.Add(new Customer(
"20", "20"));
this.customers.Add(new Customer(
"21", "21"));
this.customers.Add(new Customer(
"22", "22"));
this.customers.Add(new Customer(
"23", "23"));
this.customers.Add(new Customer(
"24", "24"));
this.customers.Add(new Customer(
"25", "25"));
this.customers.Add(new Customer(
"26", "26"));
this.customers.Add(new Customer(
"27", "27"));
this.customers.Add(new Customer(
"28", "28"));
this.customers.Add(new Customer(
"29", "29"));
this.customers.Add(new Customer(
"30", "30"));
this.customers.Add(new Customer(
"31", "31"));
this.customers.Add(new Customer(
"32", "32"));
this.customers.Add(new Customer(
"33", "33"));
this.customers.Add(new Customer(
"34", "34"));
this.customers.Add(new Customer(
"35", "35"));
this.customers.Add(new Customer(
"36", "36"));
this.customers.Add(new Customer(
"37", "37"));
this.customers.Add(new Customer(
"38", "38"));
this.customers.Add(new Customer(
"39", "39"));
this.customers.Add(new Customer(
"40", "40"));
this.customers.Add(new Customer(
"41", "42"));
// Set the row count, including the row for new records.
this.dataGridView1.RowCount = 42;
}
private void dataGridView1_CellValueNeeded(object sender,
System.Windows.Forms.DataGridViewCellValueEventArgs e)
{
listBox1.Items.Add($"dataGridView1_CellValueNeeded RowIndex {e.RowIndex}");
// 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 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 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 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 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_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 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 void btnClearLb_Click(object sender, EventArgs e)
{
listBox1.Items.Clear();
}
}
}