文本框文本仅检查一次

Question

我有2个面板。如果文本框为空，则有一条消息。我的问题是，说我进入第二个面板，然后返回并删除文本，然后再次转到第二个面板，它不会显示消息。有没有办法每次检查文本？

    private void bttn_Next_Click(object sender, EventArgs e)
    {
        if (txt_FirstName.Text == " " || txt_LastName.Text == " " ||
            txt_Email.Text == " " || txt_Contact.Text == " " ||
            txt_HouseNumber.Text == " " || txt_Street.Text == " " || 
            txt_Barangay.Text == " " || txt_Municipality.Text == "")
        {
            MessageBox.Show("Please complete all required fields.", "Message");
        }
        else
        {
            panel1.Hide();
            panel2.Hide();
            panel3.Show();
        }
    }

Answer 1

检查空字符串的正确方法如下

    private void bttn_Next_Click(object sender, EventArgs e)
    {
        if (string.IsNullOrWhiteSpace(txt_FirstName.Text) || string.IsNullOrWhiteSpace(txt_LastName.Text) ||
            string.IsNullOrWhiteSpace(txt_Email.Text) || string.IsNullOrWhiteSpace(txt_Contact.Text) ||
            string.IsNullOrWhiteSpace(txt_HouseNumber.Text) || string.IsNullOrWhiteSpace(txt_Street.Text) ||
            string.IsNullOrWhiteSpace(txt_Barangay.Text) || string.IsNullOrWhiteSpace(txt_Municipality.Text))
        {
            MessageBox.Show("Please complete all required fields.", "Message");
        }
        else
        {
            panel1.Hide();
            panel2.Hide();
            panel3.Show();
        }
    }