Another Newbie Queastion

Question

I've been trying to figure this out for a while. I have some code that looks like this:

PictureBox p = null;
PictureBox pb_dice = null;

for(int i = 1l I < 7; i++)
{
    p = this.Controls["p" + i.ToString()] as PictureBox;
    pb_dice = this.Controls["p_dice" + i.ToString()] as PictureBox;
    p.Image = WindowsFormsApplication1.Properties.Resources.diceBlank;
    pb_dice.Image = WindowsFormsApplication1.Properties.Resources.diceBlank;
}

When I run it, I get an error "Object reference not set to an instance of an object." for the pb_dice.Image, but the p.Image works fine. The resource diceBlank.png is valid and I double-
checked that both Pictureboxes are indeed pictureboxes. Both pictureboxes properties are identical and neither are part of a group or panel.

I'm using Visual Studio C# 2010 Express.
Any suggestions?

Sam Hobbs · Answer

Yes we often overlook easy things expecting the problem to be more complicated. It happens. So at least my suggestion to check for null was relevant; also checking to ensure that there really is a control with the expected id. I know that problems such as that happen.

Sam Hobbs · Answer

Yes the debugger can really help at times. I see many questions about problems that are not described adequately and the debugger could show some useful information. Since you have not had experience with the debugger it is understandable that you were not familiar with it's use in a situation such as this. I am sure you will use the debugger many more times in the future.

Jerry Fike · Answer

Yes that's so true. What also helped me was a tool I hadn't noticed before. In the debug watch window I noticed a little Text Visualizer icon in the view column. I clicked on it and saw p_dice1 (instead of pb_dice) and then it hit me.

Jerry Fike · Answer

Sam I'm an idiot! I looked and looked at that code and didn't see the obvious. pb_dice = this.Controls[p_dice + i.ToString()] as PictureBox; | | should be pb_dice That's what I get for copying and pasting to save time. I had a bunch of Pictureboxes named p1 p2 p3 etc. I would usually use pb_1 pb_2 etc but there were so many it was easier using the shorter name. Then when I created pb_dice1 2 etc. I copied the p1 p2 ... code with the intent of modifying the names. Of course I missed the pb part! Thanks for your help and sorry I took up your time.

Sam Hobbs · Answer

So let's not dwell on the inaccuracy of the code that was posted. Let's dwell on the error. What is the error message and what line of code is it on?

Jerry Fike · Answer

Not sure why using for(int i = 1; i the picturebox dice are pb_dice1 thru pb_dice6. Sure I could reference them as pb_dice  + i+1ToString() but it seems it's a little easier to understand the way I did it (and besides I did the same thing for p.Image.) [I see what you mean -- I made a mistake when I posted the first message. The code is really for(int i = 1; i  not for(int i = 1l I It errors on the first iteration of the for loop (i = 1).

Sam Hobbs · Answer

Add an if statement to check pb_dice is null before using it. If it is null then issue an error message and get out or something; do that as a permanent improvement for reliability purposes. For immediate diagnostic puposes look for the third or the tenth time or whatever that there is a control with the id p_dice1. Also are you totally sure you posted the correct code? If so then are you sure you looked closely at it? The code you posted is wrong; you don't want to set i to 1l I < 7.