Select an object based on random number in C#

Question

I want to randomly change the background colour of a picture box control. What I have is

Random Rand = new Random();
int randNum = Rand.Next(1,3);
string boxName = "pic" + randNum.ToString();
PictureBox picBox = new PictureBox();
picBox.Name = boxName;

picBox.BackColor = Color.White;

And it doesn't work. I know that picBox.Name = boxName doesn't actually set picBox to that picture box, but it's the only code that wouldn't give some intellisense error.

I have 3 picture boxes, pic1, pic2, and pic3. This is done on a button click, hence random num between 1 and 3.

I tried to apply Choosing random places in C#, but I couldn't get it to work, could anyone help?

You need to keep (or put) all of your PictureBoxes in a list or array, then get a random number to select one from that list/array. — Jonathon Reinhart
– Jonathon Reinhart, Commented Oct 23, 2013 at 0:31
if you want to load real images then you need to create a BitMap object from the file (there is a constructor that takes a file name) and then assign that image to the .BackgroundImage of the PictureBox object — pm100
– pm100, Commented Oct 23, 2013 at 0:42

MarcinJuraszek · Accepted Answer · 2013-10-23 00:32:35Z

4

Create an array of PictureBox:

var boxes = new [] { pic1, pic2, pic3 };

and use it when selecting random one:

var picBox = boxes[Rand.Next(0, 3)];

Note: You have to draw from 0 (included) to 3 (excluded), because arrays are indexed from 0.

Than you'll have a random PictureBox assigned to your picBox variable, so you can change the background:

picBox.BackColor = Color.White;

answered Oct 23, 2013 at 0:32

MarcinJuraszek

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4 Comments

codemonkeh Over a year ago

A better practice would be boxes[Rand.Next(0, boxes.Length)] in case the number of picture boxes changes in future

Gusdor Over a year ago

@codemonkeh You will get an IndexOutOfRangeException there I'm afraid. boxes[Rand.Next(0, boxes.Length-1)] would work better ;)

MarcinJuraszek Over a year ago

@Gusdor You're wrong. Random.Next takes the second parameter as exclusive.

Gusdor Over a year ago

@MarcinJuraszek so it does. School day!

codemonkeh · Accepted Answer · 2013-10-23 00:34:09Z

4

Why not simply store the colours in an array and change the background colour at random? No need to recreate a picture box.

Color[] colours = new Color[] { Color.White, Color.Black, Color.Blue, Color.Red }; //etc
Random Rand = new Random();
int randNum = Rand.Next(0, colours.Length);

And then to assign the colour:

picBox.BackColor = colours[randNum];

answered Oct 23, 2013 at 0:34

codemonkeh

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6 Comments

Razor Over a year ago

This actually answers the question!

Daevin Over a year ago

I was confused for a minute, then realized I wasn't clear in my question... I want the colour predefined, and the randomization being on the picture boxes, i.e. out of the 3 picboxes, a random one has the colour change.

codemonkeh Over a year ago

@Edper as per MSDN "A 32-bit signed integer greater than or equal to zero, and less than maxValue" Where maxValue in this case is the Length.

codemonkeh Over a year ago

@Daevin Ah in that case MarcinJuraszek's answer should be more accurate

Edper Over a year ago

@codemonkeh you're right (and my bad) I normally get confused the length/size as max value for random numbers.

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