How to check and replace null value in C#

Question

Anyone can guide me a way to check and replace null values in strList with String message "NO DATA" or allow them in dtList. Because when I met a null value in this List,it show an error like "There is no row at position..."

private DataTable getSomething1(String text){
    DataTable dtb = new DataTable();
    ...
    ...
    return dtb;
}

...

protected void buttonCheck_Click(object sender, ImageClickEventArgs e){
    List<DataTable> strList = new List<DataTable>(){
        getSomething(txtInput.Text),
        getSomething2(txtInput.Text),
        getSomething3(txtInput.Text),
        ...                
    };
}

I used C# in Webform. Plz, help me to fix this code or guide me a way to solve it. Thanks in advance.

@tech, @ riffnl: Finally I get all of your ideas and it really work now. Anw, thanks all pro here for advices. So, this is my solution ^^

private String ConvertNullToEmptyString(DataTable element)
    {
        if (element.Rows.Count > 0) //just add this condition here
        {
            if (!DBNull.Value.Equals(element.Rows[0]["FullName"]))
                return (string)element.Rows[0]["FullName"] + " ";
            else
                return String.Empty;
        }
        return "NO DATA";
    }

protected void ....(){
     List<DataTable> strList = new List<DataTable>(){
       GetItem1(txtName.Text),   //private DataTable GetItem1(String t)
       GetItem2(txtName.Text),   //...           
     };

    txtGrD_D.Text = ConvertNullToEmptyString(strList[0]);
    txtGrM_D.Text = ConvertNullToEmptyString(strList[1]);
}

If row 0 is null, then you can't parse it into string, so either check for null there or check for the row count — Paras
– Paras, Commented May 16, 2012 at 6:54

McGarnagle · Accepted Answer · 2012-05-16 06:52:24Z

8

You can use C#'s null coalescing operator ??:

string s = null;
s = s ?? "NO DATA";
// s now equals "NO DATA";

answered May 16, 2012 at 6:52

McGarnagle

103k31 gold badges235 silver badges264 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

riffnl · Accepted Answer · 2012-05-16 11:53:12Z

1

Since you're using a datatable I assume you're not talking about NULL (or nill), but DBNull.. Change your function ConvertNullToEmptyString like this:

private String ConvertNullToEmptyString(DataTable element){ 
  if (element.Rows[0]["Fullname"] == DBNull.Value || element.Rows[0]["Fullname"] == null) {
    return "NO DATA";
  } else {
    return element.Rows[0]["Fullname"].ToString();
  }
}

as requested: new sample;

// a list of datatables each containing 1 row, wasn't that the point of datatables
    // anyway -- I think you don't have any rows, so let's try this:
    private String ConvertNullToEmptyString(DataTable element)
    {
        if (element.Rows.Count == 0)
        {
            return "NO DATA";
        }
        if (element.Rows[0]["Fullname"] == DBNull.Value || element.Rows[0]["Fullname"] == null)
        {
            return "NO DATA";
        }
        else
        {
            return element.Rows[0]["Fullname"].ToString();
        }
    } 
    protected void Test()
    {
        List<DataTable> strList = new List<DataTable>(){ 
           GetItem("test1"),   //private DataTable GetItem1(String t) 
           GetItem("test2")   //...            
         };
        txtGrD_D.Text = ConvertNullToEmptyString(strList[0]);
    }

edited May 16, 2012 at 11:53

answered May 16, 2012 at 6:56

riffnl

3,1911 gold badge21 silver badges33 bronze badges

5 Comments

riffnl Over a year ago

if that's is the correct answer mark the checkmark green in front of the answer to mark it as correct - it'll improve your acceptrating.

codemanapt Over a year ago

i understand your solution. its sound logically. i change a little bit to suite my situation. but i dont know why it still be... "There is no row at position 0.". hix

codemanapt Over a year ago

can you point out my error. I've already edited my post on above like your idea

codemanapt Over a year ago

Yah. I get your ideas and do it in my way. Your idea help me find the solution in this way much. Thanks pro

user8207463 Over a year ago

I am not sure but Instead of: if (element.Rows.Count == 0) try using: if (element.Rows.Any())

Mitja Bonca · Accepted Answer · 2012-05-16 06:54:17Z

0

Try it this way by using String.IsNullOrEmpty. I double a cell in dataTable can be null.

        //creating an example table with one row (no data inisde):
        DataTable table = new DataTable();
        table.Columns.Add("FullName", typeof(string));
        table.Rows.Add("");
        string str = ConvertNullToEmptyString(table);

    //method to check for string:
    private String ConvertNullToEmptyString(DataTable element)
    {
        String s = element.Rows[0]["FullName"].ToString();
        return (string.IsNullOrEmpty(s) ? "NO DATA" : s);
    }

answered May 16, 2012 at 6:54

Mitja Bonca

4,5665 gold badges26 silver badges32 bronze badges

1 Comment

riffnl Over a year ago

indeed it can't be null it can be DBNull though

glenstorey · Accepted Answer · 2012-05-16 10:35:15Z

0

If the error is "There is no row at position...", then I guess the probelm is not that a string is null, but it is, instead, that you are trying to access a row that does not exist in the datatable.

In particular, in the line :

String s = element.Rows[0]["FullName"].ToString();

You try to access the first row of the datatable. What if the datatable is empty ? You get an error! So you should check if the datatable contains rows with something like this:

if (element.Rows.Count >0)

Answer to you comment: yes we can. modify your:

foreach (DataTable element in strList)

into something like:

foreach (DataTable element in strList)     
    {          
    if (element.Rows.Count>0)
        {
        if(strList.Any(item => item == null))          
            {                
          ConvertNullToEmptyStringelement);                                                 
            }
        txtItem1.Text = mytext ;          
        .....
        }
    else
        {
        txtItem1.Text = "No Data";          
        }      
    }

This is as far as I can go without modifying too much your program structure.

edited May 16, 2012 at 10:35

glenstorey

5,1525 gold badges42 silver badges71 bronze badges

answered May 16, 2012 at 7:08

tech

2769 silver badges13 bronze badges

5 Comments

codemanapt Over a year ago

yup. this row does not exist in the datatable. it's empty so i wanna allow them to be a string message = "NO DATA" and i dont know how to do it. can we do it, pro ?

tech Over a year ago

yes: look into the answer, I've edited it with a possible solution

codemanapt Over a year ago

can you point out my error. I've already edited my post on above like you said

tech Over a year ago

probably the error is in the line: txtGrM_D.Text = strList[1].Rows[0]["FullName"].ToString(); Here you are referencing a datatable (strList[1]) where you have not checked if there is at least one row.

codemanapt Over a year ago

uk. i got it. i've already find a way to checked it before replace it. thanks pro

Collectives™ on Stack Overflow

How to check and replace null value in C#

4 Answers 4

Comments

5 Comments

1 Comment

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

5 Comments

1 Comment

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related