无法填充在设计时创建的DataGridViewComboBoxColumn [英] Unable to populate a DataGridViewComboBoxColumn created at design time

问题描述

我在设计时添加了一个DataGridViewComboBoxColumn，但是我想在运行时进行填充。

I have a DataGridViewComboBoxColumn being craeted at design time.But I want to polulate it at runtime. But it is not happening.

这是整个代码

public partial class Form1 : Form
    {
        private List<FileInformation> FileInformationList;
        public Form1()
        {
            InitializeComponent();
            PrepareGrid();
            DisplayResult();
        }

        private void PrepareGrid()
        {

            var fileNameColumn = new DataGridViewTextBoxColumn
            {
                Name = @"FileName",
                HeaderText = "File Name",
                DataPropertyName = @"FileName",
                AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill,
                ReadOnly = false,
                Frozen = false
            };
            dataGridView1.Columns.Add(fileNameColumn);

            var downloadColumn = new DataGridViewLinkColumn

            {
                Name = @"Download",
                HeaderText = @"Download",
                DataPropertyName = @"Download",
                AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill,
                ReadOnly = true
            };
            dataGridView1.Columns.Add(downloadColumn);

            var dropdownColumn = new DataGridViewComboBoxColumn

            {
                Name = @"Test",
                HeaderText = @"Country",                
                AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill,
                ReadOnly = true
            };
            dataGridView1.Columns.Add(dropdownColumn);
        }

        private void DisplayResult()
        {
            FileInformationList = LoadItems();
            dataGridView1.DataSource = FileInformationList;

            ((DataGridViewComboBoxColumn)dataGridView1.Columns["Test"]).DataSource = GetCountryList();
            ((DataGridViewComboBoxColumn)dataGridView1.Columns["Test"]).ValueMember = "id";
            ((DataGridViewComboBoxColumn)dataGridView1.Columns["Test"]).DisplayMember = "Name";

        }

        private List<FileInformation> LoadItems()
        {
            var lstScriptInfo = new List<FileInformation>();
            for (int i = 1; i <= 5; i++)
            {
                lstScriptInfo.Add(new FileInformation { FileName = "File" + i.ToString() + ".txt" });
            }
            return lstScriptInfo;
        }

        private DataTable GetCountryList()
        {
            DataTable CountryDt = new DataTable();
            CountryDt.Columns.Add("id");
            CountryDt.Columns.Add("Name");
            CountryDt.Rows.Add("1", "Canada");
            CountryDt.Rows.Add("2", "USA");
            return CountryDt;
        }

    }

    public class FileInformation
    {
        public string FileName { get; set; }
        public string Download { get { return "Download File"; } }
    }
}

输出为

请帮助我确定问题出在哪里？

Please help me to identity what has went wrong?

推荐答案

两种实现方法：

1. 设置列的默认空值（跳过空检查）：

1. Setting defualt null value for column (skipped null checks):

var cbColumn = (DataGridViewComboBoxColumn)dataGridView1.Columns["Test"];
var ds = GetCountryList();

cbColumn.DataSource = ds;
cbColumn.ValueMember = "id";
cbColumn.DisplayMember = "Name";

cbColumn.DefaultCellStyle.NullValue = ds.Rows[0][0];
cbColumn.DefaultCellStyle.DataSourceNullValue  = ds.Rows[0][1];

第二个要在 DataBinding 并手动设置：

private void DataGridDataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
{
    foreach (DataGridViewRow row in dataGridView1.Rows)
    {
        var hasValue = row.Cells["Test"].Value != null;

        if (!hasValue)
        {
             row.Cells["Test"].Value = 1;
        }
    }
}

我还要更改绑定顺序：

private void DisplayResult()
{
    var cbColumn = (DataGridViewComboBoxColumn)dataGridView1.Columns["Test"];
    var ds = GetCountryList();

    cbColumn.DataSource = ds;
    cbColumn.ValueMember = "id";
    cbColumn.DisplayMember = "Name";

    cbColumn.DefaultCellStyle.NullValue = ds.Rows[0][0];
    cbColumn.DefaultCellStyle.DataSourceNullValue  = ds.Rows[0][1];

    FileInformationList = LoadItems();
    dataGridView1.DataSource = FileInformationList;
}

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