无法将类型 'string' 隐式转换为 'System.DateTime' - 使用 t

Question

As shown below, the error originates from what I believe is an error between translation over from Visual Basic to C#. I don't know whether this is an incorrect/outdated linked with VB, or what 'string' I'm "converting" into the time values. Need assistance on whether I must change the the structure of the if-then statement.

using System;
using System.Media;
using System.Windows.Forms;

namespace NotificationDemo
{
    public partial class NotificationDemo : Form
    {
        public NotificationDemo()
        {
            InitializeComponent();
        }

        // Variables //

        public int hour;
        public int minute;

        // Messaging System //
        public void Alert(string msg)
        {
            NotifyForm frmn = new NotifyForm();
            frmn.showAlert(msg);
        }
        private void BtnNotify_Click(object sender, EventArgs e)
        {
            this.Alert("Default Message");

            SoundPlayer player = new SoundPlayer();
            player.SoundLocation = @"C:\Windows\Media\Alarm03.wav";
            player.Play();
        }

        // Basic Schedule SysFunction 

        public string currenttime;
        public string messagetime;

        private void timer1_Tick(object sender, EventArgs e)
        {
            currenttime = DateTime.Now.ToString("hh:mm:ss tt");
            label1.Text = currenttime; 
        }

        private void timer2_Tick(object sender, EventArgs e)
        {
            messagetime = maskedTextBox1.Text + " " + comboBox1.Text;

            if (currenttime == messagetime)
            {
                timer2.Stop();
                this.Alert(textBox1.Text);
                button1.Enabled = true;
                button2.Enabled = false;

                SoundPlayer player = new SoundPlayer();
                player.SoundLocation = @"C:\Windows\Media\Alarm03.wav";
                player.Play();
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer2.Start();
            button1.Enabled = false;
            button2.Enabled = true;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer2.Stop();
            button1.Enabled = true;
            button2.Enabled = false;

        }

        // Advanced Schedule SysFunction

        public ProgramFunctionsDataContext doAction = new ProgramFunctionsDataContext();


        private void NotificationDemo_Load(object sender, EventArgs e)
        {
            // // Basic Component

            int hour = 1;
            int minute = 1;

            for (this.hour = hour; hour <= 12; hour++)
            {
                cbhour.Items.Add(hour);
            }

            for (this.minute = minute; minute <= 59; minute++)
            {
                cbminute.Items.Add(minute);
            }

            // Appointment Check

            foreach (var app in doAction.AppointmentSets)
            {
///LINE OF ERROR
                if (app.AppointmentDate = DateTime.Today.ToLongDateString())
///LINE OF ERROR
                {
                    
                }
            }
        }
    }
}

Answer 1

This is due to you are using = which is the operator to assign value

Instead, you need to use == to do the comparison for the if statement

UPDATED : As @Llama concerns that the previous solution will lead to casting error and I misinterpret the error message, so these 2 solutions can be used:

Solution 1: Directly compare based on Date

if (app.AppointmentDate.Date == DateTime.Today.Date)

Solution 2: Compare Date in string format with on ToLongDateString()

if (app.AppointmentDate.ToLongDateString() == DateTime.Today.ToLongDateString())

Solution 1 will be preferred as it is more simple and does exactly as Solution 2

While doing the comparison, be sure that both values used must be the same datatype and in Date string format if you cast it to String format.

Answer 2

Assuming you only want to compare the date component, you can rewrite your statement like this:

if (app.AppointmentDate.Date == DateTime.Today)

.Date will zero the time component, and in this case allows you to compare it to today's date.

Note the change from = to == . A single equals is an assignment, and a double equals is an equality comparison.