以数据库为源，使用 Master-Detail 视图获取详细元素的数量

Question

我使用两个DataGridViews 创建了一个主从视图，其中BindingSources 连接到同一个数据库。数据库有两个表，我在Microsoft tutorial 之后在它们之间建立了一个主从视图。这是负责它的代码：

private void GetData()
{
try
{
    // Specify a connection string. Replace the given value with a 
    // valid connection string for a Northwind SQL Server sample
    // database accessible to your system.
    String connectionString =
        "Integrated Security=SSPI;Persist Security Info=False;" +
        "Initial Catalog=Northwind;Data Source=localhost";
    SqlConnection connection = new SqlConnection(connectionString);

    // Create a DataSet.
    DataSet data = new DataSet();
    data.Locale = System.Globalization.CultureInfo.InvariantCulture;

    // Add data from the Customers table to the DataSet.
    SqlDataAdapter masterDataAdapter = new
        SqlDataAdapter("select * from Customers", connection);
    masterDataAdapter.Fill(data, "Customers");

    // Add data from the Orders table to the DataSet.
    SqlDataAdapter detailsDataAdapter = new
        SqlDataAdapter("select * from Orders", connection);
    detailsDataAdapter.Fill(data, "Orders");

    // Establish a relationship between the two tables.
    DataRelation relation = new DataRelation("CustomersOrders",
        data.Tables["Customers"].Columns["CustomerID"],
        data.Tables["Orders"].Columns["CustomerID"]);
    data.Relations.Add(relation);

    // Bind the master data connector to the Customers table.
    masterBindingSource.DataSource = data;
    masterBindingSource.DataMember = "Customers";

    // Bind the details data connector to the master data connector,
    // using the DataRelation name to filter the information in the 
    // details table based on the current row in the master table. 
    detailsBindingSource.DataSource = masterBindingSource;
    detailsBindingSource.DataMember = "CustomersOrders";
}
catch (SqlException)
{
    MessageBox.Show("To run this example, replace the value of the " +
        "connectionString variable with a connection string that is " +
        "valid for your system.");
}
}

而且效果很好。接下来，我向主视图添加了一个自定义列，并按照相同的教程使用此 sn-p 编辑主视图的外观。

// Changes how cells are displayed depending on their columns and values.
private void masterGridView_CellFormatting(object sender, 
    System.Windows.Forms.DataGridViewCellFormattingEventArgs e)
{
    // Set the background to red for negative values in the Balance column.
    if (masterGridView.Columns[e.ColumnIndex].Name.Equals("CustomColumn"))
    {

            e.CellStyle.BackColor = Color.Red;
            e.CellStyle.SelectionBackColor = Color.DarkRed;            
    }
}

现在我想在选择不同的主视图时获取每个详细视图中的行数。我会将其添加到自定义列中。这就是我卡住的地方。如何从最后一个 sn-p 中的单元格格式化程序事件中访问计数？我也可以访问视图和数据源。

Answer 1

加载数据并添加自定义列后，尝试使用DataRow.GetChildRows 方法计算详细信息视图中的行数。这将设置初始值：

DataSet ds = this.masterBindingSource.DataSource as DataSet;
string tableName = this.masterBindingSource.DataMember;

foreach (DataGridViewRow row in this.masterDataGridView.Rows)
{
    row.Cells["CustomColumn"].Value = ds.Tables[tableName].Rows[row.Index].GetChildRows(ds.Relations[0]).Length;
}

---

如果您允许用户从详细信息视图中添加/删除行，我建议首先设置以下 ⁽*⁾：

this.masterDataGridView.AllowUserToAddRows = false;
this.detailsDataGridView.AllowUserToAddRows = false;

从那里您需要附加到RowChanged 和RowDeleting 事件的详细信息DataTable：

ds.Tables["Orders"].RowChanged += Details_RowChanged;
ds.Tables["Orders"].RowDeleting += Details_RowChanged;

在该事件处理程序中，我们将再次基于GetChildRows 方法设置主行的自定义列值。特别注意事项：

• 对于已删除的行，该计数尚未反映删除。我们会考虑到这一点。
• 对于添加的行，除非您已经在添加时设置了父行，否则您需要在此处进行处理。

话虽如此：

private void Details_RowChanged(object sender, DataRowChangeEventArgs e)
{
    int change = 0;
    DataSet ds = this.masterBindingSource.DataSource as DataSet;

    if (e.Action == DataRowAction.Add)
    {
        DataRow parent = null;

        foreach (DataRow dr in ds.Tables["Customers"].Rows)
        {
            if (dr["CustomerID"].Equals(e.Row["CustomerID"]))
            {
                parent = dr;
                break;
            }
        }

        e.Row.SetParentRow(parent);
    }
    else if (e.Action == DataRowAction.Delete)
    {
        change = -1;
    }

    DataRow row = e.Row.GetParentRow(ds.Relations[0]);
    int index = ds.Tables["Customers"].Rows.IndexOf(row);

    this.masterDataGridView.Rows[index].Cells["CustomColumn"].Value = row.GetChildRows(ds.Relations[0]).Length + change;
}

---

⁽*^{)应以编程方式添加行 - DataTable.Rows.Add(params object[] values) - 添加到数据绑定 DataGridView 时。}