如何通过将单元格日期与C#.net中的当前日期进行比较来更改数据视图单元格的颜色？

Question

我是C#的新手，这是我关于C#语言的第一个项目，我的后端是Mysql，我被困在了一个特定的点上，我有一个包含与数据库值绑定的数据视图的表单，因为我有一个列" TNS_Date“--它是产品的终止日期，我希望如果TNS_Date大于当前日期，那么特定单元的背景颜色应该在colured中得到红色，我怎么能这样做，请帮我做这个。

我正在使用winforms，直到现在我还在尝试这个

foreach (DataGridViewRow row in TNSFormdgv.Rows)
{
    var now                =  DateTime.Now;
    var expirationDate     =  DateTime.Parse(row.Cells[15].Value.ToString());
    var OneMonthBefore     = expirationDate.AddDays(-30);
    if (now > OneMonthBefore && now < expirationDate)
    {
        row.DefaultCellStyle.BackColor = Color.Yellow;
    }
    else if (now > expirationDate)
    {
        row.DefaultCellStyle.BackColor = Color.Red;
    }
}

当我执行项目时，我得到了这个错误

Object reference not set to an instance of an object

这是我那份表格的全部代码，请检查我出错的地方。

public partial class TNS_Subscription : Form
{
    public TNS_Subscription()
    {
        InitializeComponent();
        TNSSubscriptionForm();
    }
    private void TNSFormBackbtn_Click(object sender, EventArgs e)
    {
        new Form2().Show();
        this.Hide();
    }
    public void TNSSubscriptionForm()
    {
        string ConString = "datasource=localhost;port=3306;username=root;password=ajay";
        MySqlConnection conDataBase = new MySqlConnection(ConString);
        MySqlCommand cmdDatabase = new MySqlCommand("Select acmecmpdetails.Cmp_Number,acmecmpdetails.Cmp_Name,acmecmpdetails.Cmp_AdminId,acmecmpdetails.Cmp_Address1,acmecmpdetails.Cmp_Country1,acmecmpdetails.Cmp_State1,acmecmpdetails.Cmp_City1,acmecmpdetails.Cmp_PostalCode,acmecmpdetails.Contact_Person1,acmecmpdetails.LandLine_Number1,acmecmpdetails.MobileNumber,acmecmpdetails.Cntct_Emailid,acmetally_detail.TallySerial_No,acmetally_detail.Tally_Release,acmetally_detail.Tally_Edition,acmetally_detail.TNS_Date,acmetally_detail.Tally_PrefPartner,acmetally_detail.Tally_accountId from acmesolutionsdatabase.acmecmpdetails INNER JOIN acmesolutionsdatabase.acmetally_detail ON acmesolutionsdatabase.acmecmpdetails.TallySerial_No= acmesolutionsdatabase.acmetally_detail.TallySerial_No;", conDataBase);


        try
        {
            MySqlDataAdapter cddsda = new MySqlDataAdapter();
            cddsda.SelectCommand = cmdDatabase;
            DataTable dbdataset = new DataTable();
            cddsda.Fill(dbdataset);
            BindingSource bsource = new BindingSource();
            bsource.DataSource = dbdataset;
            TNSFormdgv.DataSource = bsource;
            cddsda.Update(dbdataset);
            for(int i=0;i<TNSFormdgv.Rows.Count;i++)
            {
                if (Convert.ToDateTime(TNSFormdgv.Rows[i].Cells["TNS_Date"].Value.ToString()) > System.DateTime.Now.Date)
                {
                     TNSFormdgv.Rows[i].Cells["TNS_Date"].Style.BackColor = System.Drawing.Color.Red;
                }

            }
        }    
        catch (Exception ex)
        {
             MessageBox.Show(ex.Message);
        }
    }
}

提前谢谢

Answer 1

您可以简单地这样做：

for(int i=0;i<MyGridView.Rows.Count;i++)
{
    if (Convert.ToDateTime(MyGridView.Rows[i].Cells["TNS_Date"].Value.ToString()) > System.DateTime.Now.Date)
    {
        MyGridView.Rows[i].Cells["TNS_Date"].Style.BackColor = System.Drawing.Color.Red;
    }
}

如果它的值大于当前日期，它将更改单元格"TNS_Date“的背景色。

或您可以使用列TNS_Date的索引如下：

如果列TNS_Date的索引为3，那么：

for(int i=0;i<MyGridView.Rows.Count;i++)
{
    if (Convert.ToDateTime(MyGridView.Rows[i].Cells[3].Value.ToString()) > System.DateTime.Now.Date)
    {
        MyGridView.Rows[i].Cells[3].Style.BackColor = System.Drawing.Color.Red;
    }
}

我希望它能解决这个问题。

Answer 2

以下是一些可能有所帮助的示例：

  private void Form2_Load(object sender, EventArgs e)
    {
        dataGridView1.DataSourceChanged += dataGridView1_DataSourceChanged;

        List<MyClass> list = new List<MyClass>();

        list.Add(new MyClass { ID = 1, Name = "1", Date = DateTime.Now });
        list.Add(new MyClass { ID = 2, Name = "2", Date = DateTime.Now });
        list.Add(new MyClass { ID = 3, Name = "3", Date = DateTime.Now });
        list.Add(new MyClass { ID = 4, Name = "4", Date = DateTime.Now.AddDays(1) });

        dataGridView1.DataSource = list;

    }

    void dataGridView1_DataSourceChanged(object sender, EventArgs e)
    {
        // Loop through all the cells where date is in future
        foreach (DataGridViewRow row in dataGridView1.Rows)
        {
            if ((row.Cells[2].Value != null) && (DateTime)row.Cells[2].Value > DateTime.Now)
            {
                row.Cells[2].Style.BackColor = Color.Blue;
            }
        }
    }

Answer 3

我假设它在Windows窗体中，因为您使用的是datagridview。

对于datagridview，您需要遍历网格的每个单元格，以找到正确的单元格并设置背景颜色。

为此，我创建了以下代码。

void loadGrid()
{
        DataTable dtData = new DataTable();
        dtData.Columns.Add("TNS_Date");

        DataRow dRow;

        clmDate.DataPropertyName = "TNS_Date";
        dRow= dtData.NewRow();

        dRow["TNS_Date"] = "20-01-2014";
        dtData.Rows.Add(dRow);

        dRow = dtData.NewRow();

        dRow["TNS_Date"] = "20-02-2014";
        dtData.Rows.Add(dRow);


        dRow = dtData.NewRow();

        dRow["TNS_Date"] = "20-03-2014";
        dtData.Rows.Add(dRow);

        dgvGrid.DataSource = dtData;


        for (int i = 0; i <= dgvGrid.RowCount - 1; ++i)
        {
            //Finding the right cell to change colour.
            if(DateTime.Parse(dgvGrid["TNS_Date", i].Value.ToString()) >= DateTime.Now.Date)
            dgvGrid[0, i].Style.BackColor = Color.Bisque;

        }

}