Procedura: Garantire che la riga selezionata in una tabella figlio rimanga nella posizione corretta
Quando si usa il data binding in Windows Form, spesso i dati vengono mostrati in una visualizzazione denominata padre/figlio o master/dettagli Si tratta di uno scenario di data binding in cui i dati provenienti dalla stessa origine vengono visualizzati in due controlli. Se si modifica la selezione in un controllo, automaticamente vengono modificati anche i dati visualizzati nel secondo controllo. Ad esempio, il primo controllo può contenere un elenco di clienti e il secondo un elenco di ordini correlati al cliente selezionato nel primo controllo.
A partire da .NET Framework versione 2.0, quando si visualizzano i dati in una visualizzazione padre/figlio può essere necessario effettuare alcuni passaggi aggiuntivi per assicurarsi che la riga attualmente selezionata nella tabella figlio non venga reimpostata sulla prima riga della tabella. A tale scopo, è necessario memorizzare nella cache la posizione della tabella figlio e reimpostarla dopo aver modificato la tabella padre. In genere, la tabella figlio viene reimpostata la prima volta che si modifica un campo in una riga della tabella padre.
Per memorizzare nella cache la posizione corrente della tabella figlio
Dichiarare una variabile Integer per archiviare la posizione dell'elenco figlio e una variabile booleana per archiviare se memorizzare nella cache la posizione della tabella figlio.
private int cachedPosition = -1; private bool cacheChildPosition = true;Private cachedPosition As Integer = - 1 Private cacheChildPosition As Boolean = TrueGestire l'evento ListChanged per l'oggetto CurrencyManager dell'associazione e individuare un oggetto ListChangedType di Reset.
Controllare la posizione corrente dell'oggetto CurrencyManager. Se è maggiore del primo elemento dell'elenco, in genere 0, salvarlo in una variabile.
void relatedCM_ListChanged(object sender, ListChangedEventArgs e) { // Check to see if this is a caching situation. if (cacheChildPosition && cachePositionCheckBox.Checked) { // If so, check to see if it is a reset situation, and the current // position is greater than zero. CurrencyManager relatedCM = sender as CurrencyManager; if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0) // If so, cache the position of the child table. cachedPosition = relatedCM.Position; } }Private Sub relatedCM_ListChanged(ByVal sender As Object, _ ByVal e As ListChangedEventArgs) ' Check to see if this is a caching situation. If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then ' If so, check to see if it is a reset situation, and the current ' position is greater than zero. Dim relatedCM As CurrencyManager = sender If e.ListChangedType = ListChangedType.Reset _ AndAlso relatedCM.Position > 0 Then ' If so, cache the position of the child table. cachedPosition = relatedCM.Position End If End If End SubGestire l'evento CurrentChanged dell'elenco padre per l'oggetto CurrencyManager padre. Nel gestore impostare il valore booleano per indicare che non si tratta di uno scenario di memorizzazione nella cache. Se si verifica l'evento CurrentChanged, la modifica all'elemento padre sarà una modifica alla posizione dell'elenco e non una modifica al valore dell'elemento.
void bindingSource1_CurrentChanged(object sender, EventArgs e) { // If the CurrentChanged event occurs, this is not a caching // situation. cacheChildPosition = false; }' Handle the current changed event. This event occurs when ' the current item is changed, but not when a field of the current ' item is changed. Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _ ByVal e As EventArgs) Handles bindingSource1.CurrentChanged ' If the CurrentChanged event occurs, this is not a caching ' situation. cacheChildPosition = False End Sub
Per reimpostare la posizione dell'elemento figlio
Gestire l'evento PositionChanged per l'oggetto CurrencyManager del binding figlio.
Reimpostare la posizione della tabella figlio sulla posizione memorizzata nella cache salvata nella procedura precedente.
void relatedCM_PositionChanged(object sender, EventArgs e) { // Check to see if this is a caching situation. if (cacheChildPosition && cachePositionCheckBox.Checked) { CurrencyManager relatedCM = sender as CurrencyManager; // If so, check to see if the current position is // not equal to the cached position and the cached // position is not out of bounds. if (relatedCM.Position != cachedPosition && cachedPosition > 0 && cachedPosition < relatedCM.Count) { relatedCM.Position = cachedPosition; cachedPosition = -1; } } }Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) ' Check to see if this is a caching situation. If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then Dim relatedCM As CurrencyManager = sender ' If so, check to see if the current position is ' not equal to the cached position and the cached ' position is not out of bounds. If relatedCM.Position <> cachedPosition AndAlso _ cachedPosition > 0 AndAlso cachedPosition < _ relatedCM.Count Then relatedCM.Position = cachedPosition cachedPosition = -1 End If End If End Sub
Esempio
L'esempio seguente illustra come salvare la posizione corrente nell'oggetto CurrencyManager per una tabella figlio e reimpostare la posizione dopo aver effettuato una modifica nella tabella padre. In questo esempio sono presenti due controlli DataGridView associati a due tabelle in un oggetto DataSet mediante un componente BindingSource. Tra le due tabelle viene stabilita una relazione, che viene aggiunta all'oggetto DataSet. La posizione nella tabella figlio viene impostata inizialmente sulla terza riga a mero scopo esemplificativo.
using System;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace BT2
{
public class Form1 : Form
{
public Form1()
{
InitializeControlsAndDataSource();
}
// Declare the controls to be used.
private BindingSource bindingSource1;
private DataGridView dataGridView1;
private Button button1;
private DataGridView dataGridView2;
private CheckBox cachePositionCheckBox;
public DataSet set1;
private void InitializeControlsAndDataSource()
{
// Initialize the controls and set location, size and
// other basic properties.
this.dataGridView1 = new DataGridView();
this.bindingSource1 = new BindingSource();
this.button1 = new Button();
this.dataGridView2 = new DataGridView();
this.cachePositionCheckBox = new System.Windows.Forms.CheckBox();
this.dataGridView1.ColumnHeadersHeightSizeMode =
DataGridViewColumnHeadersHeightSizeMode.AutoSize;
this.dataGridView1.Dock = DockStyle.Top;
this.dataGridView1.Location = new Point(0, 20);
this.dataGridView1.Size = new Size(292, 170);
this.button1.Location = new System.Drawing.Point(18, 175);
this.button1.Size = new System.Drawing.Size(125, 23);
button1.Text = "Clear Parent Field";
this.button1.Click += new System.EventHandler(this.button1_Click);
this.dataGridView2.ColumnHeadersHeightSizeMode =
System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
this.dataGridView2.Location = new System.Drawing.Point(0, 225);
this.dataGridView2.Size = new System.Drawing.Size(309, 130);
this.cachePositionCheckBox.AutoSize = true;
this.cachePositionCheckBox.Checked = true;
this.cachePositionCheckBox.Location = new System.Drawing.Point(150, 175);
this.cachePositionCheckBox.Name = "radioButton1";
this.cachePositionCheckBox.Size = new System.Drawing.Size(151, 17);
this.cachePositionCheckBox.Text = "Cache and restore position";
this.ClientSize = new System.Drawing.Size(325, 420);
this.Controls.Add(this.dataGridView1);
this.Controls.Add(this.cachePositionCheckBox);
this.Controls.Add(this.dataGridView2);
this.Controls.Add(this.button1);
// Initialize the data.
set1 = InitializeDataSet();
// Set the data source to the DataSet.
bindingSource1.DataSource = set1;
//Set the DataMember to the Menu table.
bindingSource1.DataMember = "Customers";
// Add the control data bindings.
dataGridView1.DataSource = bindingSource1;
// Set the data source and member for the second DataGridView.
dataGridView2.DataSource = bindingSource1;
dataGridView2.DataMember = "custOrders";
// Get the currency manager for the customer orders binding.
CurrencyManager relatedCM =
bindingSource1.GetRelatedCurrencyManager("custOrders");
// Set the position in the child table for demonstration purposes.
relatedCM.Position = 3;
// Handle the current changed event. This event occurs when
// the current item is changed, but not when a field of the current
// item is changed.
bindingSource1.CurrentChanged +=
new EventHandler(bindingSource1_CurrentChanged);
// Handle the two events for caching and resetting the position.
relatedCM.ListChanged += new ListChangedEventHandler(relatedCM_ListChanged);
relatedCM.PositionChanged
+= new EventHandler(relatedCM_PositionChanged);
// Set cacheing to true in case current changed event
// occurred on set up.
cacheChildPosition = true;
}
// Establish the data set with two tables and a relationship
// between them.
private DataSet InitializeDataSet()
{
set1 = new DataSet();
// Declare the DataSet and add a table and column.
set1.Tables.Add("Customers");
set1.Tables[0].Columns.Add("CustomerID");
set1.Tables[0].Columns.Add("Customer Name");
set1.Tables[0].Columns.Add("Contact Name");
// Add some rows to the table.
set1.Tables["Customers"].Rows.Add("c1", "Fabrikam, Inc.", "Ellen Adams");
set1.Tables[0].Rows.Add("c2", "Lucerne Publishing", "Don Hall");
set1.Tables[0].Rows.Add("c3", "Northwind Traders", "Lori Penor");
set1.Tables[0].Rows.Add("c4", "Tailspin Toys", "Michael Patten");
set1.Tables[0].Rows.Add("c5", "Woodgrove Bank", "Jyothi Pai");
// Declare the DataSet and add a table and column.
set1.Tables.Add("Orders");
set1.Tables[1].Columns.Add("CustomerID");
set1.Tables[1].Columns.Add("OrderNo");
set1.Tables[1].Columns.Add("OrderDate");
// Add some rows to the table.
set1.Tables[1].Rows.Add("c1", "119", "10/04/2006");
set1.Tables[1].Rows.Add("c1", "149", "10/10/2006");
set1.Tables[1].Rows.Add("c1", "159", "10/12/2006");
set1.Tables[1].Rows.Add("c2", "169", "10/10/2006");
set1.Tables[1].Rows.Add("c2", "179", "10/10/2006");
set1.Tables[1].Rows.Add("c2", "189", "10/12/2006");
set1.Tables[1].Rows.Add("c3", "122", "10/04/2006");
set1.Tables[1].Rows.Add("c4", "130", "10/10/2006");
set1.Tables[1].Rows.Add("c5", "1.29", "10/14/2006");
DataRelation dr = new DataRelation("custOrders",
set1.Tables["Customers"].Columns["CustomerID"],
set1.Tables["Orders"].Columns["CustomerID"]);
set1.Relations.Add(dr);
return set1;
}
private int cachedPosition = -1;
private bool cacheChildPosition = true;
void relatedCM_ListChanged(object sender, ListChangedEventArgs e)
{
// Check to see if this is a caching situation.
if (cacheChildPosition && cachePositionCheckBox.Checked)
{
// If so, check to see if it is a reset situation, and the current
// position is greater than zero.
CurrencyManager relatedCM = sender as CurrencyManager;
if (e.ListChangedType == ListChangedType.Reset && relatedCM.Position > 0)
// If so, cache the position of the child table.
cachedPosition = relatedCM.Position;
}
}
void bindingSource1_CurrentChanged(object sender, EventArgs e)
{
// If the CurrentChanged event occurs, this is not a caching
// situation.
cacheChildPosition = false;
}
void relatedCM_PositionChanged(object sender, EventArgs e)
{
// Check to see if this is a caching situation.
if (cacheChildPosition && cachePositionCheckBox.Checked)
{
CurrencyManager relatedCM = sender as CurrencyManager;
// If so, check to see if the current position is
// not equal to the cached position and the cached
// position is not out of bounds.
if (relatedCM.Position != cachedPosition && cachedPosition
> 0 && cachedPosition < relatedCM.Count)
{
relatedCM.Position = cachedPosition;
cachedPosition = -1;
}
}
}
int count = 0;
private void button1_Click(object sender, EventArgs e)
{
// For demo purposes--modifies a value in the first row of the
// parent table.
DataRow row1 = set1.Tables[0].Rows[0];
row1[1] = DBNull.Value;
}
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
}
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms
Public Class Form1
Inherits Form
Public Sub New()
InitializeControlsAndDataSource()
End Sub
' Declare the controls to be used.
Private WithEvents bindingSource1 As BindingSource
Private dataGridView1 As DataGridView
Private WithEvents button1 As Button
Private dataGridView2 As DataGridView
Private cachePositionCheckBox As CheckBox
Public set1 As DataSet
Private Sub InitializeControlsAndDataSource()
' Initialize the controls and set location, size and
' other basic properties.
Me.dataGridView1 = New DataGridView()
Me.bindingSource1 = New BindingSource()
Me.button1 = New Button()
Me.dataGridView2 = New DataGridView()
Me.cachePositionCheckBox = New System.Windows.Forms.CheckBox()
Me.dataGridView1.ColumnHeadersHeightSizeMode = _
DataGridViewColumnHeadersHeightSizeMode.AutoSize
Me.dataGridView1.Dock = DockStyle.Top
Me.dataGridView1.Location = New Point(0, 20)
Me.dataGridView1.Size = New Size(292, 170)
Me.button1.Location = New System.Drawing.Point(18, 175)
Me.button1.Size = New System.Drawing.Size(125, 23)
button1.Text = "Clear Parent Field"
Me.dataGridView2.ColumnHeadersHeightSizeMode = _
System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize
Me.dataGridView2.Location = New System.Drawing.Point(0, 225)
Me.dataGridView2.Size = New System.Drawing.Size(309, 130)
Me.cachePositionCheckBox.AutoSize = True
Me.cachePositionCheckBox.Checked = True
Me.cachePositionCheckBox.Location = New System.Drawing.Point(150, 175)
Me.cachePositionCheckBox.Name = "radioButton1"
Me.cachePositionCheckBox.Size = New System.Drawing.Size(151, 17)
Me.cachePositionCheckBox.Text = "Cache and restore position"
Me.ClientSize = New System.Drawing.Size(325, 420)
Me.Controls.Add(Me.dataGridView1)
Me.Controls.Add(Me.cachePositionCheckBox)
Me.Controls.Add(Me.dataGridView2)
Me.Controls.Add(Me.button1)
' Initialize the data.
set1 = InitializeDataSet()
' Set the data source to the DataSet.
bindingSource1.DataSource = set1
'Set the DataMember to the Menu table.
bindingSource1.DataMember = "Customers"
' Add the control data bindings.
dataGridView1.DataSource = bindingSource1
' Set the data source and member for the second DataGridView.
dataGridView2.DataSource = bindingSource1
dataGridView2.DataMember = "custOrders"
' Get the currency manager for the customer orders binding.
Dim relatedCM As CurrencyManager = _
bindingSource1.GetRelatedCurrencyManager("custOrders")
' Handle the two events for caching and resetting the position.
AddHandler relatedCM.ListChanged, AddressOf relatedCM_ListChanged
AddHandler relatedCM.PositionChanged, AddressOf relatedCM_PositionChanged
' Set the position in the child table for demonstration purposes.
relatedCM.Position = 3
' Set cacheing to true in case current changed event
' occurred on set up.
cacheChildPosition = True
End Sub
' Establish the data set with two tables and a relationship
' between them.
Private Function InitializeDataSet() As DataSet
set1 = New DataSet()
' Declare the DataSet and add a table and column.
set1.Tables.Add("Customers")
set1.Tables(0).Columns.Add("CustomerID")
set1.Tables(0).Columns.Add("Customer Name")
set1.Tables(0).Columns.Add("Contact Name")
' Add some rows to the table.
set1.Tables("Customers").Rows.Add("c1", "Fabrikam, Inc.", _
"Ellen Adams")
set1.Tables(0).Rows.Add("c2", "Lucerne Publishing", "Don Hall")
set1.Tables(0).Rows.Add("c3", "Northwind Traders", "Lori Penor")
set1.Tables(0).Rows.Add("c4", "Tailspin Toys", "Michael Patten")
set1.Tables(0).Rows.Add("c5", "Woodgrove Bank", "Jyothi Pai")
' Declare the DataSet and add a table and column.
set1.Tables.Add("Orders")
set1.Tables(1).Columns.Add("CustomerID")
set1.Tables(1).Columns.Add("OrderNo")
set1.Tables(1).Columns.Add("OrderDate")
' Add some rows to the table.
set1.Tables(1).Rows.Add("c1", "119", "10/04/2006")
set1.Tables(1).Rows.Add("c1", "149", "10/10/2006")
set1.Tables(1).Rows.Add("c1", "159", "10/12/2006")
set1.Tables(1).Rows.Add("c2", "169", "10/10/2006")
set1.Tables(1).Rows.Add("c2", "179", "10/10/2006")
set1.Tables(1).Rows.Add("c2", "189", "10/12/2006")
set1.Tables(1).Rows.Add("c3", "122", "10/04/2006")
set1.Tables(1).Rows.Add("c4", "130", "10/10/2006")
set1.Tables(1).Rows.Add("c5", "1.29", "10/14/2006")
Dim dr As New DataRelation("custOrders", _
set1.Tables("Customers").Columns("CustomerID"), _
set1.Tables("Orders").Columns("CustomerID"))
set1.Relations.Add(dr)
Return set1
End Function '
Private cachedPosition As Integer = - 1
Private cacheChildPosition As Boolean = True
Private Sub relatedCM_ListChanged(ByVal sender As Object, _
ByVal e As ListChangedEventArgs)
' Check to see if this is a caching situation.
If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
' If so, check to see if it is a reset situation, and the current
' position is greater than zero.
Dim relatedCM As CurrencyManager = sender
If e.ListChangedType = ListChangedType.Reset _
AndAlso relatedCM.Position > 0 Then
' If so, cache the position of the child table.
cachedPosition = relatedCM.Position
End If
End If
End Sub
' Handle the current changed event. This event occurs when
' the current item is changed, but not when a field of the current
' item is changed.
Private Sub bindingSource1_CurrentChanged(ByVal sender As Object, _
ByVal e As EventArgs) Handles bindingSource1.CurrentChanged
' If the CurrentChanged event occurs, this is not a caching
' situation.
cacheChildPosition = False
End Sub
Private Sub relatedCM_PositionChanged(ByVal sender As Object, ByVal e As EventArgs)
' Check to see if this is a caching situation.
If cacheChildPosition AndAlso cachePositionCheckBox.Checked Then
Dim relatedCM As CurrencyManager = sender
' If so, check to see if the current position is
' not equal to the cached position and the cached
' position is not out of bounds.
If relatedCM.Position <> cachedPosition AndAlso _
cachedPosition > 0 AndAlso cachedPosition < _
relatedCM.Count Then
relatedCM.Position = cachedPosition
cachedPosition = -1
End If
End If
End Sub
Private count As Integer = 0
Private Sub button1_Click(ByVal sender As Object, _
ByVal e As EventArgs) Handles button1.Click
' For demo purposes--modifies a value in the first row of the
' parent table.
Dim row1 As DataRow = set1.Tables(0).Rows(0)
row1(1) = DBNull.Value
End Sub
<STAThread()> _
Shared Sub Main()
Application.EnableVisualStyles()
Application.SetCompatibleTextRenderingDefault(False)
Application.Run(New Form1())
End Sub
End Class
Per testare l'esempio di codice, eseguire la procedura seguente:
Eseguire l'esempio.
Verificare che la casella di controllo Memorizza nella cache e reimposta posizione sia selezionata.
Fare clic sul pulsante Cancella campo padre per provocare una modifica in un campo della tabella padre. Notare che la riga selezionata nella tabella figlio non cambia.
Chiudere ed eseguire nuovamente l'esempio. È necessario eseguire questa procedura perché la reimpostazione si verifica solo in seguito alla prima modifica nella riga padre.
Deselezionare la casella di controllo Memorizza nella cache e reimposta posizione.
Fare clic sul pulsante Cancella campo padre. Notare che la riga selezionata nella tabella figlio diventa la prima riga.
Compilazione del codice
L'esempio presenta i requisiti seguenti:
- Riferimenti agli assembly System, System.Data, System.Drawing, System.Windows.Forms e System.XML.
Vedi anche
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