Randomize object position

Question

hey everyone,

I'm making a little quiz-style application but I've got a few issues.

I random the questions from a NSMutableArray using arc4random(), then I populate the view with 3 buttons, one which includes a correct answer and the other 2 include two wrong answers

what I need to do is to randomize the X coordinate (position) of the 3 buttons in the view this is the code I'm using, but it gives me problems as it doesn't work properly nd the app often crashes when calling the action:

NSBundle *bundle02 = [NSBundle mainBundle];
NSString *textFilePath02 = [bundle02 pathForResource:@"possiblePositions" ofType:@"txt"];   
NSString *fileContents02 = [NSString stringWithContentsOfFile:textFilePath02 encoding:NSUTF8StringEncoding error:nil];
arrayPossiblePositions = [[NSMutableArray alloc] initWithArray:[fileContents02 componentsSeparatedByString:@"\n"]];

int length02 = [arrayPossiblePositions count];
int chosen02 = arc4random() % length02;
[arrayPossiblePositions removeObjectAtIndex:chosen02];
int chosen04 = arc4random() % length02;
[arrayPossiblePositions removeObjectAtIndex:chosen04];
int chosen05 = arc4random() % length02;

if ([questionString isEqualToString:@"question1"]) {

    buttonCorrect = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize = CGRectMake(chosen02, 80, 130, 130);
    buttonCorrect.frame = newSize;
    [buttonCorrect setImage:[UIImage imageNamed:@"kncpf.png"] forState:UIControlStateNormal];
    [buttonCorrect addTarget:self action:@selector(answerCorrect) forControlEvents:UIControlEventTouchUpInside];
    [main addSubview:buttonCorrect];

    buttonUncorrect01 = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize02 = CGRectMake(chosen04, 80, 130, 130);
    buttonUncorrect01.frame = newSize02;
    [buttonUncorrect01 setImage:[UIImage imageNamed:@"kncpf02.png"] forState:UIControlStateNormal];
    [buttonUncorrect01 addTarget:self action:@selector(answerUncorrect) forControlEvents:UIControlEventTouchUpInside];
    [main addSubview:buttonUncorrect01];

    buttonUncorrect02 = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize034578 = CGRectMake(chosen05, 80, 130, 130);
    buttonUncorrect02.frame = newSize034578;
    [buttonUncorrect02 setImage:[UIImage imageNamed:@"kncpf034578.png"] forState:UIControlStateNormal];
    [buttonUncorrect02 addTarget:self action:@selector(answerUncorrect) forControlEvents:UIControlEventTouchUpInside];
    [main addSubview:buttonUncorrect02];
}

can you suggest me doing something different, because I'm really getting crazy ?

Thanks in advance for answers, David

Answer 1

I actually needed to do something similar, but instead of moving the images around, I decided instead to do this:

• Create three buttons where you want them to appear (predetermined locations).
• Assign the images to each button randomly (by randomizing a NSMutableArray with the NSStrings of the image names).
• Instead of assigning @selector(answerCorrect) and @selector(answerUncorrect), assign @selector(checkIfCorrect:)
• Define checkIfCorrect as such:

-(void)checkIfCorrect:(id)sender{ UIImage *buttonImage = sender.image;

if(buttonImage == [UIImage imageNamed:@"kncpf.png"]){ [self answerCorrect]; } else { [self answerIncorrect]; }

}

EDITED TO INCLUDE THE CODE I RECOMMEND:

Also, you are calling

int length02 = [arrayPossiblePositions count];
int chosen02 = arc4random() % length02;
[arrayPossiblePositions removeObjectAtIndex:chosen02];
int chosen04 = arc4random() % length02;
[arrayPossiblePositions removeObjectAtIndex:chosen04];
int chosen05 = arc4random() % length02;

Notice that length02 remains the same, while the size of arrayPossiblePositions changes. This is probably the first reason why your code crashes: you are trying to remove an index from an array which is outside of the array count!

I have not tested, but should work: (dont forget to define checkanswer() as I mentioned above)

NSMutableArray *imagesArray = [NSMutableArray arrayWithObjects:@"image1.png", @"image2.png", @"image3.png", nil];

int count1 = [imagesArray count];
int index1 = arc4random() % count1;

button1 = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize = CGRectMake(30, 80, 130, 130);
    button1.frame = newSize;
    [button1 setImage:[UIImage imageNamed:[imagesArray objectAtIndex:index1]] forState:UIControlStateNormal];
    [button1 addTarget:self action:@selector(checkAnswer:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button1];

[imagesArray removeObjectAtIndex:index1];
int count2 = [imagesArray count];
int index2 = arc4random() % count2;

button2 = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize = CGRectMake(160, 80, 130, 130);
    button2.frame = newSize;
    [button2 setImage:[UIImage imageNamed:[imagesArray objectAtIndex:index2]] forState:UIControlStateNormal];
    [button2 addTarget:self action:@selector(checkAnswer:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button2];

[imagesArray removeObjectAtIndex:index2];
int count3 = [imagesArray count];
int index3 = arc4random() % count3;

button3 = [UIButton buttonWithType:UIButtonTypeCustom];
    CGRect newSize = CGRectMake(290, 80, 130, 130);
    button3.frame = newSize;
    [button3 setImage:[UIImage imageNamed:[imagesArray objectAtIndex:index3]] forState:UIControlStateNormal];
    [button3 addTarget:self action:@selector(checkAnswer:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button3];

Answer 2

I think arc4random () needs an upper bounds. Not sure if the modulo use is correct here or more likely a semantic error, not sure how arc reacts when you try and perform an operation like that without first setting it's upper bounds. I'm not sure, try subbing in a hard value instead of your length02 and see if you're getting the expected behavior, then work backwards from there.