字符串的確包含了對isullorwhitespace的定義

Question

請幫助我。 我不知道isnullorwhitespace什么問題：

我的錯誤是：

“字符串確實包含對isullorwhitespace的定義”

我對isnullorwhitespace其他選擇是isnullorwhitespace ？

private void btnAdd_Click(object sender, EventArgs e)
{
    int age = int.Parse(txtage.Text);
    if (string.IsNullOrWhiteSpace(txtfname.Text))
    {
        MessageBox.Show("Please input your firstname!");
    }
    else if(string.IsNullOrWhiteSpace(txtlname.Text))
    {
        MessageBox.Show("Please input your lastname!");
    }
    else if(string.IsNullOrWhiteSpace(cbgender.SelectedItem.ToString()))
    {
        MessageBox.Show("Please specify your gender!");
    }
    else if(string.IsNullOrWhiteSpace(txtage.Text) || age <= 0 )
    {
        MessageBox.Show("Please assign your birthdate to know your age!");
    }
    else if(string.IsNullOrWhiteSpace(txtcontact.Text))
    {
        MessageBox.Show("Please input your contact number!");
    }
    else if(string.IsNullOrWhiteSpace(txtAddress.Text))
    {
        MessageBox.Show("Please input your address!");
    }
    else if(string.IsNullOrWhiteSpace(txtUsername.Text))
    {
        MessageBox.Show("Please input your username!");
    }   
    else if(string.IsNullOrWhiteSpace(txtPass.Text))
    {
        MessageBox.Show("Please input your password!");
    }
    else if(string.IsNullOrWhiteSpace(cbxQuest.SelectedItem.ToString()))
    {
        MessageBox.Show("Please specify your secret question!");
    }
    else if(string.IsNullOrWhiteSpace(txtAsnwer.Text))
    {
        MessageBox.Show("Please input your answer!");
    }
    else 
    {

        //Insert 7
        ui.fname = txtfname.Text;
        ui.lname = txtlname.Text;
        ui.gender = cbgender.SelectedItem.ToString();
        ui.age = int.Parse(txtage.Text);
        ui.bdate = dtpBdate.Value;
        ui.contactNo = txtcontact.Text;
        ui.Adress = txtAddress.Text;
        //Insert 4
        us.username = txtUsername.Text;
        us.passwordHash = txtPass.Text;
        us.secretQuestion = cbxQuest.SelectedItem.ToString();
        us.secretAnswer = txtAsnwer.Text;

        StoredProcedure.Insert(ui, us);
        dgData.DataSource = StoredProcedure.View();
        Clear();
    }

Answer 1

.NET 4中引入了String.IsNullOrWhiteSpace。如果您不針對.NET 4，則可以輕松編寫自己的代碼：

public static class StringExtensions
{
    public static bool IsNullOrWhiteSpace(string value)
    {
        if (value != null)
        {
            for (int i = 0; i < value.Length; i++)
            {
                if (!char.IsWhiteSpace(value[i]))
                {
                    return false;
                }
            }
        }
        return true;
    }
}

可以這樣使用：

if (StringExtensions.IsNullOrWhiteSpace(txtfname.Text))
{
// do something
}