c# - 我只需要处理特定选定表的列名

Question

当我从 ComboBox 中选择一个表时，我会得到该表中存在的每一列(以及在我检查它时隐藏它的选项)。

当我从“组合框”中选择下一个表格时，我得到了新表格列以及第一个表格中的前一个表格。

如何解决这个问题并只保存选定的表格列？

private void ComboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    var tableName = comboBox1.SelectedItem;

    sqlDa = new SqlDataAdapter($"SELECT * FROM {tableName}", form1.conn = new SqlConnection($"Server = {form1.ServerBox.Text }; Database = { form1.DBBox.Text}; Trusted_Connection = True"));
    dataTable = new DataTable();
    sqlDa.Fill(dataTable);
    dataGridView1.DataSource = dataTable;

    foreach (DataGridViewColumn column in dataGridView1.Columns)
    {
        var item = (ToolStripMenuItem)contextMenuStrip1.Items.Add(column.HeaderText);
        var item2 = comboBox2.Items.Add(column.HeaderText);
        item.Tag = column.Name;
        item.Checked = column.Visible;
        item.CheckOnClick = true;

        item.CheckedChanged += (obj, args) =>
        {
            var i = (ToolStripMenuItem)obj;
            dataGridView1.Columns[(string)i.Tag].Visible = i.Checked;
        };
    }            
}

Answer 1

您需要先清除 contextMenuStrip1 的 Items 集合，然后再填充它。它可以通过 contextMenuStrip1.Items.Clear() 简单地完成，但是为了防止应用程序中可能出现句柄/内存泄漏，最好在删除菜单项后立即处理它们:

var items = contextMenuStrip1.Items.Cast<ToolStripItem>().ToList();
contextMenuStrip1.Items.Clear();
items.ForEach(x => x.Dispose());

示例

这是一个工作示例，它需要一个 DataGridView、一个 ComboBox 和一个 ContextMenuStrip。它将数据库的表加载到 ComboBox 中，当您从 ComboBox 中选择索引时，它将所选表的数据加载到 DataGridView 中，并且如果您右键单击 DataGridView 的列标题，将显示一个 ContextMenuStrip，允许您设置列的可见性:

string server = ".";
string db = "TestDB";
private void Form1_Load(object sender, System.EventArgs e)
{
    var connection = $"SERVER={server};DATABASE={db};Integrated Security=true";

    //Hanlde combo box selected index changed
    comboBox1.SelectedIndexChanged += (obj1, args1) =>
    {
        dataGridView1.DataSource = null;
        if (comboBox1.SelectedIndex > -1)
        {
          //Fill data table and show data in data grid view
          var data = GetDataTable($"SELECT * FROM {comboBox1.SelectedValue}", connection);
          dataGridView1.Columns.Clear();
          dataGridView1.DataSource = data;
        }

        //Clear existing items of context menu strip
        var items = contextMenuStrip1.Items.Cast<ToolStripItem>().ToList();
        contextMenuStrip1.Items.Clear();
        items.ForEach(x => x.Dispose());

        //Add the columns to context menu strip
        foreach (DataGridViewColumn c in dataGridView1.Columns)
        {
            var item = (ToolStripMenuItem)contextMenuStrip1.Items.Add(c.HeaderText);
            item.Tag = c.Name;
            item.Checked = c.Visible;
            item.CheckOnClick = true;
            //Hanlde CheckStateChanged event of context menu strip items
            item.CheckStateChanged += (obj, args) =>
            {
                var i = (ToolStripMenuItem)obj;
                dataGridView1.Columns[(string)i.Tag].Visible = i.Checked;
            };
        }
    };

    //Load table names
    var tables = GetDataTable("SELECT Name FROM Sys.Tables", connection);
    comboBox1.ValueMember = "Name";
    comboBox1.DisplayMember = "Name";
    comboBox1.DataSource = tables;

    //Show context menu strip on right click on data grid veiw header
    dataGridView1.CellMouseClick += (obj, args) =>
    {
        if (args.RowIndex == -1 && args.Button == MouseButtons.Right)
            contextMenuStrip1.Show(Cursor.Position);
    };
}

DataTable GetDataTable(string commandText, string connectionString)
{
    using (var da = new SqlDataAdapter(commandText, connectionString))
    {
        var dt = new DataTable();
        da.Fill(dt);
        return dt;
    }
}