StreamReader throwing Exception

Question

4.00/5 (1 vote)

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Hi,
I am using the following code for reading a text file.

C#

string filename = Path.Combine(path, comboBox1.SelectedItem.ToString() + ".rbl");

StreamReader sr = new StreamReader(filename);
Rules.Rows.Clear();
string line;
while ((line = sr.ReadLine()) != null)
{

        if (sr.ReadLine().Contains("Bool"))
        {
            string[] line1 = Regex.Split(sr.ReadLine().ToString(), ",");
            if (line1[1] == "And")
            {
                RbAnd.Checked = true;
                RbOr.Checked = false;
            }
            else
            {
                RbAnd.Checked = false;
                RbOr.Checked = true;
            }
        }

        if (sr.ReadLine().Contains(",") && !sr.ReadLine().Contains("Bool"))
        {
            string[] line2 = Regex.Split(sr.ReadLine().ToString(), ",");
            string val1 = line2[0];
            string val2 = line2[1];
            string val3 = "";
            if (line2.Length == 3)
            {
                if (line2[2] != "")
                {
                    val3 = line2[2];
                }
            }

            Rules.Rows.Add(val1, val2, val3);
        }

}
sr.Close();

and it throwing NullReferenceException. Anyone can help me to find out the error in my code.

Posted 28-Oct-14 2:39am

Manu Prasad

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Comments

Herman<T>.Instance 28-Oct-14 8:41am

at what line?

Manu Prasad 28-Oct-14 8:42am

if (sr.ReadLine().Contains(",") && !sr.ReadLine().Contains("Bool"))

Herman<T>.Instance 28-Oct-14 8:44am

You use a lot of times ReadLine(). That moves a pointer in the file!
Use the line variable to check what you want

Manu Prasad 28-Oct-14 8:43am

this is my file

Bool ,Or
Added On,Does not equal,test1
Created On,Contains,test2

2 solutions

Solution 1

Yes, tThe StreamReader contructor may throw, indeed (see the documentation: "StreamReader Constructor (String)" at MSDN[^]).
As wise developer, you should handle the exception.

Posted 28-Oct-14 2:45am

CPallini

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Herman<T>.Instance · Accepted Answer · 2014-10-28T02:49:00

Solution 2

My Solution:

C#

using (StreamReader sr = new StreamReader(filename))
{
    Rules.Rows.Clear();
    string line;
    while ((line = sr.ReadLine()) != null)
    {

        if (line.Contains("Bool"))
        {
            string[] line1 = Regex.Split(line, ",");
            if (line1[1] == "And")
            {
                RbAnd.Checked = true;
                RbOr.Checked = false;
            }
            else
            {
                RbAnd.Checked = false;
                RbOr.Checked = true;
            }
        }

        if (line.Contains(",") && !line.Contains("Bool"))
        {
            string[] line2 = Regex.Split(line, ",");
            string val1 = line2[0];
            string val2 = line2[1];
            string val3 = string.Empty;
            if (!string.IsNullOrEmpty(line2[2]) && line2.Length.Equals(3))
            {
                val3 = line2[2];
            }
            Rules.Rows.Add(val1, val2, val3);
        }

    }
    sr.Close();
}

Posted 28-Oct-14 2:49am

Herman<T>.Instance

Comments

Manu Prasad 28-Oct-14 8:51am

Thank you!!!

Herman<T>.Instance 28-Oct-14 8:52am

URWelcome

BillWoodruff 28-Oct-14 9:25am

+5

Manu Prasad 28-Oct-14 9:26am

What?

Herman<T>.Instance 28-Oct-14 10:22am

URWelcome == You Are welcome
+5 means he likes the solution too

Manu Prasad 29-Oct-14 0:09am

:)

Manu Prasad 29-Oct-14 0:11am

Digimanus can u tell me the reason for the error and how the solution is works there..? (Please consider I am a beginner in C#...)

Herman<T>.Instance 29-Oct-14 6:45am

Simple. Your file has 3 lines. Each time you call ReadLine(), you read a line from the file and the pointer moves to the next line.
In your case you started reading the first line in the 'while ((line = sr.ReadLine()) != null)' statement, the 2nd line in the 'if (sr.ReadLine().Contains("Bool"))', the 3rd line in if (sr.ReadLine().Contains(",") and the 4th line in '&& !sr.ReadLine().Contains("Bool")'. But you had 3 lines in the file, so the 4th line lead to the exception.
In my case I first use 'using (StreamReader sr = new StreamReader(filename))'. By using the USING keyword the IDisposable methods of the StreamReader is used. So the object is properly disposed after you are ready using it.
Second. When I have read a line I want to check for the value in the read line, not in a new read line. That is why it works.

So read about IDisposable and proper use of the StreamReader object.

Good luck

Manu Prasad 30-Oct-14 6:32am

Thank you sooo much... :)