如何通过类实例返回引用？

Question

我正在尝试构建一个通用的自定义选择器表单。根据类构造函数的不同，它应该返回单个值或值列表。

public partial class DGV_Select_Multiple : Form
{
    public bool Answered { get; set; } = false; // Indicates if user picked something
    public string Result { get; set; } = ""; // Single picked result
    public List<string> Result_List { get; set; } = new List<string>(); // Multiple picked results
    public List<string> Default_List { get; set; } = new List<string>(); // Default highlighted values

    private bool MultipleSelection { get; set; } = false; // Flag of single/multiple selection allowed

    public DGV_Select_Multiple(IEnumerable<string> List, string Default)
    {
        // Default value is a single string => single selection available only
        InitializeComponent();
        this.MultipleSelection = false;
        this.Default_List = new List<string> { Default };
        
        b_confirm.Click += delegate { ConfirmSelection(); };
        b_cancel.Click += delegate { this.Close(); };
    }

    public DGV_Select_Multiple(IEnumerable<string> List, List<string> Default_List)
    {
        // Default is a List<string> => multiple selections are available
        InitializeComponent();
        this.MultipleSelection = true;
        this.Default_List = Default_List;
        b_confirm.Click += delegate { ConfirmSelection(); };
        b_cancel.Click += delegate { this.Close(); };
    }

    private void ConfirmSelection()
    {
        this.Answered = true;
        if (MultipleSelection)
        {
            Result_List = new List<string> { "value1", "value2" };
        }
        else
        {
            Result = "some single string";
        }
    }
}

每次使用这样一个冗余操作所需的类返回值：

bool Answered = false;
string Result = "";
var AskForm = new DGV_Select_Multiple(new List<string> { "v1", "v2" }, "");
AskForm.Show();

if (AskForm.Answered)
{
   Result = AskForm.Result;
}

我尝试在类构造函数中使用ref字符串，但最终没有改变。有任何方法可以简化上面的构造函数吗？

string Result = new DGV_Select_Multiple(new List<string> { "v1", "v2" }, "").Result;

或者类似的东西。感谢你的任何帮助

Answer 1

将逻辑移到静态工厂方法中。因为您有两个返回类型，所以需要两个方法，但它们可以有相同的名称。

class DGV_Select_Multiple
{
    public static List<string> Show(List<string> list, List<string> defaultList)
    {
        var f = New DGV_Select_Multiple(list, defaultList);
        f.Show();

        return f.Answered ? f.Result as string : null;
    }

    public static string Show(List<string> list, string defaultString)
    {
        var f = New DGV_Select_Multiple(list, defaultString);
        f.Show();

        return f.Answered ? f.Result as List<string> : null;
    }

    //Etc....

现在，当您需要使用该表单时，只需编写：

string result= DGV_Select_Multiple.Show(new List<string> { "v1", "v2" }, "");

或

List<string> result= DGV_Select_Multiple.Show(new List<string> { "v1", "v2" }, new List<string> { "" });

Answer 2

名为DGV_Select_Multiple的表单用于选择单个字符串值或多个字符串值，其中包括：

DataGridView DGV;
Label lb_Question;
Button b_confirm;
Button b_cancel;

完整的表单代码如下：

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;

namespace Sample
{
    public partial class DGV_Select_Multiple : Form
    {
        public bool Answered { get; set; } = false;
        public string Result { get; set; } = "";
        public List<string> Result_List { get; set; } = new List<string>();
        public List<string> Default_List { get; set; } = new List<string>();
        private bool MultipleSelection { get; set; } = false;
        public DGV_Select_Multiple(string Text, IEnumerable<string> List, string Default)
        {
            InitializeComponent();

            lb_Question.Text = Text;
            if (!string.IsNullOrWhiteSpace(Default)) this.Default_List = new List<string> { Default };

            #region Bind single selection
            MultipleSelection = false;
            DGV.Columns.Add("Value", "Value");
            DGV.Columns[0].Width = DGV.Width - 22;
            DGV.MultiSelect = false;
            foreach (string str in List)
            {
                DGV.Rows.Add(str);
            }
            DGV.ClearSelection();
            #endregion

            b_confirm.Click += delegate { ConfirmSelection(); };
            b_cancel.Click += delegate { this.Close(); };
        }
        public DGV_Select_Multiple(string Text, IEnumerable<string> List, List<string> Default_List)
        {
            InitializeComponent();

            lb_Question.Text = Text;
            if (Default_List != null) this.Default_List = Default_List;

            #region Bind multiple selection
            MultipleSelection = true;
            DGV.Columns.Add("Value", "Значение");
            DGV.Columns.Add("Selected", "V");
            DGV.Columns["Selected"].DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleCenter;
            DGV.Columns[1].Width = 30;
            DGV.Columns[0].Width = DGV.Width - 30 - 22;
            foreach (string str in List)
            {
                DGV.Rows.Add(str);
            }
            DGV.ClearSelection();

            foreach (DataGridViewColumn Col in DGV.Columns)
            {
                Col.SortMode = DataGridViewColumnSortMode.NotSortable;
            }
            #endregion

            DGV.SelectionChanged += delegate
            {
                if (MultipleSelection)
                {
                    try
                    {
                        if ((DGV.SelectedCells != null && DGV.SelectedCells.Count != 0) || (DGV.SelectedRows != null && DGV.SelectedRows.Count != 0))
                        {
                            int Row = DGV.SelectedCells[0].RowIndex;
                            int Col = DGV.SelectedCells[0].ColumnIndex;
                            if (Row >= 0 && Col >= 0)
                            {
                                if (DGV.Rows[Row].Cells["Selected"].Value == null || DGV.Rows[Row].Cells["Selected"].Value == DBNull.Value || string.IsNullOrWhiteSpace(DGV.Rows[Row].Cells["Selected"].Value.ToString()))
                                {
                                    DGV.Rows[Row].Cells["Selected"].Value = "V";
                                    DGV.Rows[Row].DefaultCellStyle.BackColor = Color.LightGreen;
                                }
                                else
                                {
                                    DGV.Rows[Row].Cells["Selected"].Value = "";
                                    DGV.Rows[Row].DefaultCellStyle.BackColor = SystemColors.Window;
                                }
                                DGV.ClearSelection();
                                DGV.Refresh();
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine("Error: " + ex.ToString());
                    }

                }
            };
            DGV.ColumnHeaderMouseClick += delegate (object sender, DataGridViewCellMouseEventArgs e)
            {
                try
                {
                    if (DGV.Columns[e.ColumnIndex].GetType() == typeof(DataGridViewCheckBoxColumn) || DGV.Columns[e.ColumnIndex].Name == "Selected")
                    {
                        if (DGV.Rows.Count != 0)
                        {
                            bool check = (DGV.Rows.Cast<DataGridViewRow>().Where(x => x.Cells["Selected"].Value.ToString() != "V").Count() != 0);
                            foreach (DataGridViewRow DGVRow in DGV.Rows)
                            {
                                DGVRow.Cells["Selected"].Value = (check ? "V" : "");
                                DGVRow.DefaultCellStyle.BackColor = check ? Color.LightGreen : SystemColors.Window;
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error: " + ex.ToString());
                }
            };

            b_confirm.Click += delegate { ConfirmSelection(); };
            b_cancel.Click += delegate { this.Close(); };
        }

        private void DGV_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
        {
            if (!MultipleSelection)
            {
                if (e.Clicks == 2 && e.RowIndex >= 0 && e.ColumnIndex >= 0)
                {
                    ConfirmSelection();
                }
            }
        }
        private void ConfirmSelection()
        {
            try
            {
                Answered = true;
                if (MultipleSelection && DGV.Columns.Contains("Selected"))
                {
                    Result_List = DGV.Rows.Cast<DataGridViewRow>().Where(x => x.Cells["Selected"].Value != null && x.Cells["Selected"].Value != DBNull.Value && x.Cells["Selected"].Value.ToString() == "V").Select(x => x.Cells["Value"].Value.ToString()).ToList();
                }
                else if (DGV.SelectedRows != null && DGV.SelectedRows.Count != 0)
                {
                    Result = DGV.SelectedRows[0].Cells["Value"].Value.ToString();
                }
                this.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error: " + ex.ToString());
            }
        }
        private void DGV_Select_Multiple_Load(object sender, EventArgs e)
        {
            DGV.SizeChanged += delegate
            {
                try
                {
                    if (DGV.Columns.Count == 1)
                    {
                        DGV.Columns[0].Width = DGV.Width - 22;
                    }
                    else
                    {
                        DGV.Columns[0].Width = DGV.Width - 30 - 22;
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error: " + ex.ToString());
                }
            };
            this.Shown += delegate
            {
                try
                {
                    if (DGV.Columns.Contains("Selected"))
                    {
                        foreach (DataGridViewRow DGVRow in DGV.Rows)
                        {
                            DGVRow.Cells["Selected"].Value = "";
                            DGVRow.DefaultCellStyle.BackColor = SystemColors.Window;
                        }
                    }

                    if (Default_List != null && Default_List.Count != 0)
                    {
                        if (DGV.Rows.Count != 0)
                        {
                            DGV.ClearSelection();
                            if (DGV.Columns.Contains("Selected"))
                            {
                                foreach (DataGridViewRow DGVRow in DGV.Rows)
                                {
                                    string str = DGVRow.Cells["Value"].Value.ToString();
                                    if (Default_List != null && Default_List.Contains(str))
                                    {
                                        DGVRow.Cells["Selected"].Value = "V";
                                        DGVRow.Cells["Selected"].Selected = true;
                                        DGVRow.Selected = true;
                                    }
                                }
                            }
                            else
                            {
                                foreach (DataGridViewRow DGVRow in DGV.Rows)
                                {
                                    string str = DGVRow.Cells["Value"].Value.ToString();
                                    if (Default_List != null && Default_List.Contains(str))
                                    {
                                        DGVRow.Selected = true;
                                    }
                                }
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error: " + ex.ToString());
                }
            };
        }
    }
    public partial class DGV_Select_Multiple
    {
        public static List<string> ShowDialog(string Text, List<string> list, List<string> defaultList)
        {
            var f = new DGV_Select_Multiple(Text, list, defaultList);
            f.ShowDialog();
            return f.Answered ? f.Result_List : null;
        }

        public static string ShowDialog(string Text, List<string> list, string defaultString)
        {
            var f = new DGV_Select_Multiple(Text, list, defaultString);
            f.ShowDialog();
            return f.Answered ? f.Result : null;
        }
    }
}

单个选择的用法：

string Question = DGV_Select_Multiple.ShowDialog("Please select a value...", new List<string> { "Value 1", "Value 2", "Value 3" }, defaultString: "Value 2");
if (Question  != null)
{
    MessageBox.Show("Answered single option " + Question );
}
else
{
    MessageBox.Show("Used not answered...");
}

多重选择的用法：

List<string> Question = DGV_Select_Multiple.ShowDialog("Please select a value...", new List<string> { "Value 1", "Value 2", "Value 3" }, defaultList: new List<string> { "Value 2"});
if (Question  != null)
{
    MessageBox.Show("Answered multiple options " + string.Join(", ", Question));
}
else
{
    MessageBox.Show("Used not answered...");
}

提示:若要访问Visual窗体设计器临时，请删除以下代码：

public partial class DGV_Select_Multiple
{
    public static List<string> ShowDialog(string Text, List<string> list, List<string> defaultList)
    {
        var f = new DGV_Select_Multiple(Text, list, defaultList);
        f.ShowDialog();
        return f.Answered ? f.Result_List : null;
    }
    public static string ShowDialog(string Text, List<string> list, string defaultString)
    {
        var f = new DGV_Select_Multiple(Text, list, defaultString);
        f.ShowDialog();
        return f.Answered ? f.Result : null;
    }
}