Como assegurar que a linha selecionada em uma tabela filho permaneça na posição correta

Artigo
10/19/2023

Muitas vezes, ao trabalhar com a vinculação de dados nos Windows Forms, você exibirá dados no que é chamado de modo de exibição pai/filho ou detalhes/mestre. Isso se refere a um cenário de associação de dados em que os dados da mesma fonte são exibidos em dois controles. Alterar a seleção em um controle faz com que os dados exibidos no segundo controle mudem. Por exemplo, o primeiro controle pode conter uma lista de clientes e o segundo, uma lista de pedidos relacionada ao cliente selecionado no primeiro controle.

Iniciando com o .NET Framework versão 2.0, quando você exibe dados no modo de exibição pai/filho, pode ser necessário executar etapas adicionais para que a linha selecionada atualmente na tabela filho não seja redefinida para a primeira linha da tabela. Para fazer isso, será preciso armazenar em cache a posição da tabela filho e redefini-la após a alteração da tabela pai. Normalmente, a redefinição do filho ocorre na primeira vez que um campo em uma linha da tabela pai muda.

Para armazenar em cache a posição filho atual

Declare uma variável de inteiro para armazenar a posição de lista filho e uma variável booliana para indicar se a posição filho deve ser armazenada em cache.
```
private int cachedPosition = -1;
private bool cacheChildPosition = true;
```
```
Private cachedPosition As Integer = - 1
Private cacheChildPosition As Boolean = True
```
Manipule o ListChanged evento para as ligações CurrencyManager e verifique se há um ListChangedType de Reset.

Verifique a posição atual do CurrencyManager. Se for maior que a primeira entrada na lista (normalmente 0), salve-a em uma variável.

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 Sub

Manipule o evento da lista pai para o gerenciador de CurrentChanged moedas pai. No manipulador, defina o valor booliano para indicar que este não é um cenário de cache. Se ocorrer CurrentChanged , a alteração no pai será uma alteração de posição de lista e não uma alteração de valor de item.

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

Para redefinir a posição filho

Manipule o PositionChanged evento para a associação CurrencyManagerfilho .

Redefina a posição da tabela filho para a posição em cache salva no procedimento anterior.

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

Exemplo

O exemplo a seguir demonstra como salvar a CurrencyManagerposição atual na tabela .for uma tabela filho e redefinir a posição depois que uma edição for concluída na tabela pai. Este exemplo contém dois DataGridView controles vinculados a duas tabelas em um DataSet componente de uso BindingSource . Uma relação é estabelecida entre as duas tabelas e a relação é adicionada DataSetao . A posição na tabela filho inicialmente é definida como a terceira linha para fins de demonstração.

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

Para testar o exemplo de código, execute as etapas a seguir:

Execute o exemplo.
Marque a caixa de seleção Armazenar em cache e redefinir posição.
Clique no botão Limpar campo pai para provocar uma alteração em um campo da tabela pai. Observe que a linha selecionada na tabela filho não muda.
Feche e execute o exemplo novamente. Você precisa fazer isso porque o comportamento de reinicialização ocorre apenas na primeira alteração da linha pai.
Desmarque a caixa de seleção Armazenar em cache e redefinir posição.
Clique no botão Limpar campo pai. Observe que a linha selecionada na tabela filho muda para a primeira linha.

Compilando o código

Este exemplo requer:

Referência aos assemblies System, System.Data, System.Drawing, System.Windows.Forms e System.XML.

Compartilhar via

Como assegurar que a linha selecionada em uma tabela filho permaneça na posição correta

Para armazenar em cache a posição filho atual

Para redefinir a posição filho

Exemplo

Compilando o código

Confira também

Recursos adicionais