在C＃中将null分配给整数

Question

I have a winforms application and i am trying to pass 5 parameters inside the tableadapter in order to execute a query but i get the error "Cannot convert from 'int?' to 'int'. All of them can be nulls.

private int? c_id ;
private string c_cn;
private int? c_afm;
private string c_job;
private string c_city;

private void btnView_Click(object sender, EventArgs e) {
c_id = (txtBox_id.Text != string.Empty) ? c_id = Convert.ToInt32(txtBox_id.Text) : c_id = null;
c_afm = (txtBox_afm.Text != string.Empty) ? c_afm = Convert.ToInt32(txtBox_afm.Text) : c_afm = null;
c_cn = (txtBox_cn.Text != string.Empty) ? c_cn = txtBox_cn.Text : c_cn = null;
c_job = (txtBox_job.Text != string.Empty) ? c_job = txtBox_job.Text : c_job = null;
c_city = (txtBox_job.Text != string.Empty) ? c_city = txtBox_city.Text : c_city = null;

this.clientBrowserTableAdapter.Fill(erpDataSet.PelatesBrowser,c_id,c_cn,c_afm, c_job,c_city);
}

The problem is at c_id and c_afm parameters. Any ideas?

Answer 1

You can create a dedicated method for converting string to int?

private int? ConvertToDbInt(string text)
{
    if (string.IsNullOrEmpty(text))
    {
        return null;
    }

    return int.Parse(text);
}

Then reuse it for different variables

c_id = ConvertToDbInt(txtBox_id.Text);
c_afm = ConvertToDbInt(txtBox_afm.Text);

Your actual problem is because conditional operator ?: expects that both positive and negative expressions produce value of same type, where in your case it is int - for positive and int? for negative.

Either the type of first_expression and second_expression must be the same , or an implicit conversion must exist from one type to the other.

If you big fan of conditional operator ?: then just make sure that both expression returns same type, int? in your case.

c_id = (txtBox_id.Text != string.Empty) ? (int?)Convert.ToInt32(txtBox_id.Text) : null;

When exception thrown on line this.clientBrowserTableAdapter.Fill(... , that mean that Fill method expects parameter of type int , you can easily convert nullable int to int by calling .GetValueOrDefault()

this.clientBrowserTableAdapter.Fill(
    erpDataSet.PelatesBrowser,
    c_id.GetValueOrDefault(),
    c_cn,
    c_afm.GetValueOrDefault(), 
    c_job,
    c_city);

Answer 2

clientBrowserTableAdapter.Fill is expecting an int . You are passing a Nullable<int> , they are not the same and there is no implicit conversion happening. You either need to cast it to int ie (int)c_id or use .Value property of Nullable<T> . If c_id is null, then you will have to deal with that case otherwise you will get exception when casting.

As a side note, your assignment is slightly off, you can just do :

c_id = (txtBox_id.Text != string.Empty) ? Convert.ToInt32(txtBox_id.Text) : (int?)null;;