Null reference exception occurs for no reason
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Hi, I use this class to read XML file and get color information of DataGridView rows. When I run, compiler says: System.NullReferenceException: 'Object reference not set to an instance of an object.' My class is:
public static void ReadDataGridViewSettings(System.Windows.Forms.DataGridView dgv)
{
XmlDocument xmldoc = new XmlDocument();
XmlNodeList xmlnode;
FileStream fs = new FileStream(Application.StartupPath + @"\MyGrid.xml", FileMode.Open, FileAccess.Read);
xmldoc.Load(fs);
xmlnode = xmldoc.GetElementsByTagName("Row");
for (int i = 0; i <= dgv.Rows.Count; i++)
{
int cellcolor = int.Parse(xmlnode[i].ChildNodes.Item(0).InnerText.Trim());
int textcolor = int.Parse(xmlnode[i].ChildNodes.Item(1).InnerText.Trim());
if (cellcolor != 0)
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.FromArgb(Convert.ToInt32(cellcolor));
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.FromArgb(Convert.ToInt32(textcolor));
}
else
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.White;
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.Black;
}
}
fs.Close();
}My XML file has this structure:
-677434
0
0
0How can I fix it?
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Hi, I use this class to read XML file and get color information of DataGridView rows. When I run, compiler says: System.NullReferenceException: 'Object reference not set to an instance of an object.' My class is:
public static void ReadDataGridViewSettings(System.Windows.Forms.DataGridView dgv)
{
XmlDocument xmldoc = new XmlDocument();
XmlNodeList xmlnode;
FileStream fs = new FileStream(Application.StartupPath + @"\MyGrid.xml", FileMode.Open, FileAccess.Read);
xmldoc.Load(fs);
xmlnode = xmldoc.GetElementsByTagName("Row");
for (int i = 0; i <= dgv.Rows.Count; i++)
{
int cellcolor = int.Parse(xmlnode[i].ChildNodes.Item(0).InnerText.Trim());
int textcolor = int.Parse(xmlnode[i].ChildNodes.Item(1).InnerText.Trim());
if (cellcolor != 0)
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.FromArgb(Convert.ToInt32(cellcolor));
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.FromArgb(Convert.ToInt32(textcolor));
}
else
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.White;
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.Black;
}
}
fs.Close();
}My XML file has this structure:
-677434
0
0
0How can I fix it?
This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself. Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable. It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterday's shirt when you took it off last night. We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket! Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't. But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values. But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!
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Hi, I use this class to read XML file and get color information of DataGridView rows. When I run, compiler says: System.NullReferenceException: 'Object reference not set to an instance of an object.' My class is:
public static void ReadDataGridViewSettings(System.Windows.Forms.DataGridView dgv)
{
XmlDocument xmldoc = new XmlDocument();
XmlNodeList xmlnode;
FileStream fs = new FileStream(Application.StartupPath + @"\MyGrid.xml", FileMode.Open, FileAccess.Read);
xmldoc.Load(fs);
xmlnode = xmldoc.GetElementsByTagName("Row");
for (int i = 0; i <= dgv.Rows.Count; i++)
{
int cellcolor = int.Parse(xmlnode[i].ChildNodes.Item(0).InnerText.Trim());
int textcolor = int.Parse(xmlnode[i].ChildNodes.Item(1).InnerText.Trim());
if (cellcolor != 0)
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.FromArgb(Convert.ToInt32(cellcolor));
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.FromArgb(Convert.ToInt32(textcolor));
}
else
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.White;
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.Black;
}
}
fs.Close();
}My XML file has this structure:
-677434
0
0
0How can I fix it?
Alex Dunlop wrote:
compiler says: System.NullReferenceException
The compiler doesn't generate that exception; the runtime does. If it was a compiler error, you wouldn't be able to run your application at all, because you wouldn't be able to compile it.
Alex Dunlop wrote:
new FileStream(Application.StartupPath + @"\MyGrid.xml"
You shouldn't try to write files in the same directory as your application. When it's deployed, it will most likely be stored under the "Program Files" directory, and it would need to run as an admin account to have permission to write to its own directory. See Where Should I Store My Data?[^] for suggestions of more appropriate locations to save your files.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
Hi, I use this class to read XML file and get color information of DataGridView rows. When I run, compiler says: System.NullReferenceException: 'Object reference not set to an instance of an object.' My class is:
public static void ReadDataGridViewSettings(System.Windows.Forms.DataGridView dgv)
{
XmlDocument xmldoc = new XmlDocument();
XmlNodeList xmlnode;
FileStream fs = new FileStream(Application.StartupPath + @"\MyGrid.xml", FileMode.Open, FileAccess.Read);
xmldoc.Load(fs);
xmlnode = xmldoc.GetElementsByTagName("Row");
for (int i = 0; i <= dgv.Rows.Count; i++)
{
int cellcolor = int.Parse(xmlnode[i].ChildNodes.Item(0).InnerText.Trim());
int textcolor = int.Parse(xmlnode[i].ChildNodes.Item(1).InnerText.Trim());
if (cellcolor != 0)
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.FromArgb(Convert.ToInt32(cellcolor));
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.FromArgb(Convert.ToInt32(textcolor));
}
else
{
dgv.Rows[i].DefaultCellStyle.BackColor = Color.White;
dgv.Rows[i].DefaultCellStyle.ForeColor = Color.Black;
}
}
fs.Close();
}My XML file has this structure:
-677434
0
0
0How can I fix it?
What this Exeption generally means is allready explained. The Mistake you made in your code is the loop. Your limit is i<= DGV.Rows.Count - but it must be i < DGV.Rows.Count. Change that and it could work ... The Elements from the DGV are from 0...DGV.Rows.Count-1 (because the Collection in it is Zero-based ...
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What this Exeption generally means is allready explained. The Mistake you made in your code is the loop. Your limit is i<= DGV.Rows.Count - but it must be i < DGV.Rows.Count. Change that and it could work ... The Elements from the DGV are from 0...DGV.Rows.Count-1 (because the Collection in it is Zero-based ...
Thanks. I changed it to
i<=xmlNode.Count-1
and solved. Now, I can retrieve all my color setting in each row.
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Alex Dunlop wrote:
compiler says: System.NullReferenceException
The compiler doesn't generate that exception; the runtime does. If it was a compiler error, you wouldn't be able to run your application at all, because you wouldn't be able to compile it.
Alex Dunlop wrote:
new FileStream(Application.StartupPath + @"\MyGrid.xml"
You shouldn't try to write files in the same directory as your application. When it's deployed, it will most likely be stored under the "Program Files" directory, and it would need to run as an admin account to have permission to write to its own directory. See Where Should I Store My Data?[^] for suggestions of more appropriate locations to save your files.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
I told him that a month ago ... How to link SQL CE database file to the directory where EXE file of the application exists?[^] :sigh:
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony "Common sense is so rare these days, it should be classified as a super power" - Random T-shirt AntiTwitter: @DalekDave is now a follower!
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Thanks. I changed it to
i<=xmlNode.Count-1
and solved. Now, I can retrieve all my color setting in each row.
You are welcome ... :)
