Creating an array of labels for use later - annoying problem, please help!

[Paul F. Johnson]

Hi,

Got a fun one here.

In the Designer file, I have defined my array of labels like this

System.Windows.Forms.Label[] periodlabel = new
System.Windows.Forms.Label[10];

then at the bottom

private System.Windows.Forms.Label[] periodlabel;

The reason for this is that I want to be able to create on the between 1
and 10 labels. The problem is this...

My source looks like this

public partial class lessonplan : Form
{
    public lessonplan(int noperiods)
    {
        float periodSize = 100.0F / (float)noperiods;
        InitializeComponent();
        this.lesson.ColumnCount = noperiods + 1;
        this.lesson.ColumnStyles.Add(new
System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Absolute,
120F));
        for (int i = 0; i < noperiods; ++i)
        {
                this.lesson.ColumnStyles.Add(new
System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent,
periodSize));
                this.periodlabel[i].Location = new System.Drawing.Point(127 + (117 *
i), 2);
            this.periodlabel[i].Text = "Lesson " + i.ToString();
                this.periodlabel[i].AutoSize = true;
                this.periodlabel[i].Font = new System.Drawing.Font("Arial", 18F,
System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point,
((byte)(0)));
                this.periodlabel[i].Size = new System.Drawing.Size(109, 27);
                this.periodlabel[i].TabIndex = i + 6;
this.lesson.Controls.Add(this.periodlabel[i], 0, i);
        }
}

The source compiles fine (well, it tells me that Field
'timetabler.lessonplan.periodlabel is never assigned to, and will always
have its default value null, but from what I've read, that's ok) , but
when I run the application and click on the button which instantates the
lessonplan class (it is passing a value happily, if I remove the
periodlabel code, everything works find), I get

System.NullReferenceException: Object reference not set to an instance
of an object

I've tried a number of solutions to this (including putting a
periodlabel[i] = new Label(); just before the addition of the
periodlabel values but within the braces, trying to create dummy
instances in the designer source file and a few other tricks found
online - nothing worked).

Is there a nice, easy way of doing what I want here?

TTFN

Paul

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[Jonathan Pobst]

The following works, so I guess you need to work from it to see what the
difference is:

private void Form1_Load(object sender, EventArgs e)
{
     int count = 5;

     Label[] periodlabel = new Label[count];

     for (int i = 0; i < count; i++)
     {
         periodlabel[i] = new Label();
         periodlabel[i].Text = string.Format("Hello {0}", i);
     }

     Console.WriteLine(periodlabel[0].Text);
}

Actually, scratch that, it looks like you are declaring periodlabel twice:

 > System.Windows.Forms.Label[] periodlabel = new
 > System.Windows.Forms.Label[10];
 >
 > then at the bottom
 >
 > private System.Windows.Forms.Label[] periodlabel;

Jonathan

Paul wrote:

> Hi,
>
> Got a fun one here.
>
> In the Designer file, I have defined my array of labels like this
>
> System.Windows.Forms.Label[] periodlabel = new
> System.Windows.Forms.Label[10];
>
> then at the bottom
>
> private System.Windows.Forms.Label[] periodlabel;
>
> The reason for this is that I want to be able to create on the between 1
> and 10 labels. The problem is this...
>
> My source looks like this
>
> public partial class lessonplan : Form
> {
>     public lessonplan(int noperiods)
>     {
> float periodSize = 100.0F / (float)noperiods;
> InitializeComponent();
> this.lesson.ColumnCount = noperiods + 1;
> this.lesson.ColumnStyles.Add(new
> System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Absolute,
> 120F));
> for (int i = 0; i < noperiods; ++i)
> {
> this.lesson.ColumnStyles.Add(new
> System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent,
> periodSize));
> this.periodlabel[i].Location = new System.Drawing.Point(127 + (117 *
> i), 2);
>             this.periodlabel[i].Text = "Lesson " + i.ToString();
> this.periodlabel[i].AutoSize = true;
> this.periodlabel[i].Font = new System.Drawing.Font("Arial", 18F,
> System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point,
> ((byte)(0)));
> this.periodlabel[i].Size = new System.Drawing.Size(109, 27);
> this.periodlabel[i].TabIndex = i + 6;
> this.lesson.Controls.Add(this.periodlabel[i], 0, i);
> }
> }
>
> The source compiles fine (well, it tells me that Field
> 'timetabler.lessonplan.periodlabel is never assigned to, and will always
> have its default value null, but from what I've read, that's ok) , but
> when I run the application and click on the button which instantates the
> lessonplan class (it is passing a value happily, if I remove the
> periodlabel code, everything works find), I get
>
> System.NullReferenceException: Object reference not set to an instance
> of an object
>
> I've tried a number of solutions to this (including putting a
> periodlabel[i] = new Label(); just before the addition of the
> periodlabel values but within the braces, trying to create dummy
> instances in the designer source file and a few other tricks found
> online - nothing worked).
>
> Is there a nice, easy way of doing what I want here?
>
> TTFN
>
> Paul
>
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Mono-winforms-list maillist  -  Mono-winforms-list@...
> http://lists.ximian.com/mailman/listinfo/mono-winforms-list

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[Paul F. Johnson]

Hi,

> Actually, scratch that, it looks like you are declaring periodlabel twice:

periodlabel is defined in the Designer source (created by SharpDevelop).
It was 5 separate labels, but I changed it to an array of labels.

The definition within the class instantation code doesn't matter - the
code dies with or without it with the same error.

TTFN

Paul

--
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