如何在每行附近添加一个复选框？

Question

int counter; CheckBox[] _cbs;

ScrollLabel._lines contain 151l ines. counter is int

I want that on line 0 and then each 3 lines to add a checkbox in the beginning of the line with one space to the right so there will be one space place between the text in the line and the checkBox.

Now im getting exception in the loop on the line:

private void button1_Click(object sender, EventArgs e)
        {
            if (this.button1.Text == "stop")
            {
                this.button1.Text = "start";
                this.scrollLabel1.StopTimer();
                for (int i = 0; i < ScrollLabel._lines.Length; i++)
                {
                    counter += 3;
                    _cbs[i] = new CheckBox();
                    _cbs[i].Location = new Point(0, counter);
                    this.scrollLabel1.Controls.Add(_cbs[i]);

                }
            }
            else
            {
                this.button1.Text = "stop";
                this.scrollLabel1.MilliSecsSpeed = (int)this.numericUpDown1.Value;
                this.scrollLabel1.StartTimer();
            } 
        }

_cbs[i] = new CheckBox();

_cbs is null.

This is the constructor:

counter = 0;
            this.scrollLabel1.MouseWheel += new MouseEventHandler(ScrollLabel1_MouseWheel);
            this.scrollLabel1.MouseEnter += ScrollLabel1_MouseEnter;
            readableRss = RssReader.covertRss("http://rotter.net/rss/rotternews.xml");
            RssReader.CnnRss();
            this.DoubleBuffered = true;
            this.scrollLabel1.Text = readableRss;//File.ReadAllText(@"Demo.txt");
            this.scrollLabel1.MilliSecsSpeed = (int)this.numericUpDown1.Value;
            this.scrollLabel1.YStep = (float)this.numericUpDown2.Value;
            this.scrollLabel1.Words = new List<WordColor>();
            this.scrollLabel1.Words.Add(new WordColor() { WordOrText = "scrollLabel1", ForeColor = Color.Red, ColorOnlyThisWord = true, BackColor = Color.LightBlue });
            this.scrollLabel1.Words.Add(new WordColor() { WordOrText = "using", ForeColor = Color.Blue, DrawRect = true, RectColor = Color.Black, BackColor = Color.Wheat });


            this.scrollLabel1.PopLinesOnNonBmpMode = this.checkBox6.Checked;

            this.scrollLabel1.BitmapModus = this.checkBox4.Checked;
            this.scrollLabel1.TextLayoutCentered = this.checkBox5.Checked;
            this.scrollLabel1.AdditionalLinesAtEnd = (int)this.numericUpDown3.Value;

            for (int i = 0; i < ScrollLabel._lines.Length; i++)
            {
                _cbs = new CheckBox[i];
            }

This is how the loop in the button click look like now:

for (int i = 0; i < ScrollLabel._lines.Length; i++)
                {
                    counter += 3;
                    _cbs[i].Location = new Point(0, counter);
                    this.scrollLabel1.Controls.Add(_cbs[i]);

                }

But all the _cbs are null inside.

EDIT**

for (int i = 0; i < ScrollLabel._lines.Length; i++)
                {
                    _cbs[i] = new CheckBox();
                    counter += 3;
                    _cbs[i].Location = new Point(0, counter);
                    this.scrollLabel1.Controls.Add(_cbs[i]);

                }

Not getting null but i dont see checkBox near/in the beginning of each 3 lines why ?

Answer 1

_cbs is an array which you have declared and you are reallocating in your constructor:

for (int i = 0; i < ScrollLabel._lines.Length; i++)
        {
            _cbs = new CheckBox[i]; // This line reallocates the array as a larger array each time through the loop!
        }

You need to define the array only once :

CheckBox[] _cbs = new CheckBox[ScrollLabel._lines.Length];

Then you allocate individual checkboxes to the elements of the array:

for (int i = 0; i < ScrollLabel._lines.Length; i++) {
  _cbs[i] = new CheckBox(); // This allocates a new checkbox for the i-th element
}

To place a checkbox on every third line, try something like this:

int lineHeight = 20;                   // pixels, set this to whatever your line height is
int checkboxInterval = lineHeight * 3; // every third line
int numCheckboxes = ScrollLabel._lines.Length / 3;
for (int i = 0; i < numCheckboxes; i++) {
  _cbs[i] = new CheckBox();
  _cbs[i].Location = new Point(0, i * checkboxInterval);
  this.scrollLabel1.Controls.Add(_cbs[i]);
}

Note that you only need one-third as many checkboxes as the number of lines.