Array of Class initializing

Question

4.00/5 (1 vote)

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C#

Hallo,

I have defined one array of class in the main program and I get an error when I try to use it.

The definition in the main program is

C#

public const int NumColumns = 10;
public static GridViewComp[] gridView = new GridViewComp[NumColumns];

GridViewComp Class contains: string Title, int Width, bool Show.

In another form, I try to assign the values from an XML file

private void AssignGridSetup()
{
    var columns = XDocument.Load(Program.setupFileName).Element("Setup").Element("Columns");
    int iLoop = 0;
    foreach (GridViewComp myComp in Program.gridView)
    {
        var item = columns.Element(Program.columnElement[iLoop]);
        myComp.Title = item.Element("Title").Value;
        myComp.Width = Convert.ToInt32(item.Element("Width").Value);
        myComp.Show = Convert.ToBoolean(item.Element("Show").Value);
        iLoop++;
    }
}

(the xml part works fine)

When I execute the code, I become the following error:
"Object reference not set to an instance of an object" in the line

myComp.Title = item.Element("Title").Value;

I have looked for a solution, and I should initialize every element of the array, including the initialize instruction

private void AssignGridSetup()
{
    var columns = XDocument.Load(Program.setupFileName).Element("Setup").Element("Columns");
    int iLoop = 0;
    foreach (GridViewComp myComp in Program.gridView)
    {
        var item = columns.Element(Program.columnElement[iLoop]);
        myComp = new GridViewComp();
        myComp.Title = item.Element("Title").Value;
        myComp.Width = Convert.ToInt32(item.Element("Width").Value);
        myComp.Show = Convert.ToBoolean(item.Element("Show").Value);
        iLoop++;
    }
}

But when I do so, the compiler shows the following error:
myNamespace.GridViewComp.GridViewComp() is inaccessible due to its protection level
and marks the underlined part.

I also tried with a "for" loop instead of "foreach"

private void AssignGridSetup()
{
    var columns = XDocument.Load(Program.setupFileName).Element("Setup").Element("Columns");
    for (int iLoop = 0; iLoop < Program.NumColumns; iLoop++ )
    {
        var item = columns.Element(Program.columnElement[iLoop]);
        Program.gridView[iLoop] = new GridViewComp();
        Program.gridView[iLoop].Title = item.Element("Title").Value;
        Program.gridView[iLoop].Width = Convert.ToInt32(item.Element("Width").Value);
        Program.gridView[iLoop].Show = Convert.ToBoolean(item.Element("Show").Value);
    }
}

but the result is the same.

Has anybody any idea of how can I fill the array with the xml data, or what I could be doing wrong?

Thank you very much in advance.

David
(PS: I use MS VS2010)

Posted 18-Mar-13 2:52am

NeueStudium2012

Updated 18-Mar-13 3:02am

v4

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3 solutions

Solution 1

Hi,

Exception is because Object value is not assigned and you are using from that index.

Make sure you have gridView object with filled information before accessing its index.

hope this help you to identify the issue.

thanks
-Amit

Posted 18-Mar-13 3:03am

AmitGajjar

Comments

NeueStudium2012 18-Mar-13 9:07am

Hallo Amit,
That is why I tryed with the initializing sentence.
But I do not know the values before reading them from the xml file.

AmitGajjar 18-Mar-13 9:11am

In that case you can assign default value, if it is of Integer Array then you can assign zero for length that you want. if you will not assign any value and try to access it's value at particular index then it will gives you object reference exception because it's memory allocation is not done. memory allocation will done only after assigning value.

NeueStudium2012 18-Mar-13 9:45am

and how can I do that?
It is not so simple, it is a class, and the number of elements can be large, so it need a loop to do so.
But with the initializing sentence, the compiler drops an error.

AmitGajjar 19-Mar-13 1:47am

if you do not have constraint to use Array then you can use List as well. use one constructor to fill your list/Array.

Solution 3

Finally, I got one solution:

The values must be initialized within the round brackets, instead of initialize the array and later on assign the values.

C#

private void AssignGridSetup()
{
    var columns = XDocument.Load(Program.setupFileName).Element("Setup").Element("Columns");
    for (int iLoop = 0; iLoop < Program.NumColumns; iLoop++ )
    {
        var item = columns.Element(Program.columnElement[iLoop]);
        Program.gridView[iLoop] = new GridViewComp(
            item.Element("Title").Value, 
            Convert.ToInt32(item.Element("Width").Value), 
            Convert.ToBoolean(item.Element("Show").Value));
    }
}

Thank you everybody for your comments.

David

Posted 18-Mar-13 3:59am

NeueStudium2012

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NeueStudium2012 · Accepted Answer · 2013-03-18T03:58:00

Finally, I got one solution:

C#

private void AssignGridSetup()
{
    var columns = XDocument.Load(Program.setupFileName).Element("Setup").Element("Columns");
    for (int iLoop = 0; iLoop < Program.NumColumns; iLoop++ )
    {
        var item = columns.Element(Program.columnElement[iLoop]);
        Program.gridView[iLoop] = new GridViewComp(
            item.Element("Title").Value, 
            Convert.ToInt32(item.Element("Width").Value), 
            Convert.ToBoolean(item.Element("Show").Value));
    }
}