Objective-C: Logic Question - objective-c

Question

Hey guys, I'm getting a little trouble here. I have a view that makes a grid display. I mean, I have 9 items and sets to display 3 per line. Resulting in 3 lines. That's OK. What I don't understang, it's why always I get a space between them. Sometimes it comes up and on the middle of the lines. The space is equal to one line height.
Check the code:
NSInteger quantidadeDeVideos = [self.videosURL count];
NSInteger contadorDeVideos = 0;
NSInteger idLinha = 0;
NSInteger linha = 1;
NSInteger itemq = 0;
while (contadorDeVideos < quantidadeDeVideos) {
float f;
float g;
// Set the lines
if (itemq < 3) {
itemq++;
}
else {
itemq = 1;
linha++;
}
// This makes the second line multiplies for 150;
if (linha > 1) {
g = 150;
}
else {
g = 0;
}
// Ignore this, this is foi make 1,2,3. Making space between the itens.
if (idLinha > 2) {
idLinha = 0;
}
NSLog(#"%i", foi);
float e = idLinha*250+15;
f = linha*g;
UIImageView *thumbItem = [[UIImageView alloc] init];
thumbItem.frame = CGRectMake(e, f, 231, 140);
UIColor *bkgColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:#"VideosItemBackground.png"]];
thumbItem.backgroundColor = bkgColor;
thumbItem.opaque = NO;
[self.videosScroll addSubview:thumbItem];
contadorDeVideos++;
idLinha++;
}
This is the result should be:
[][][]
[][][]
[][][]
And this is what I'm getting:
[][][]
[][][]
[][][]
Thanks for all!

Answer 1

When linha is 1, g is 0, making linha * g 0. For the subsequent lines, g is 150, making linha * g == 300 for the second iteration (a jump of 300 over the first), after which it increases by 150 each time. Instead of conditionally setting g each time through, you should just make it a constant 150 and then either use (linha - 1) * g for the value of f or just start linha at 0.
If you want to see how to spot the problem yourself:
Ask yourself, what is going wrong here?
The rectangles are being drawn one row too low
It only happens after the first row
So we look at the line that's responsible for where the rectangles are drawn:
thumbItem.frame = CGRectMake(e, f, 231, 140)
The variable f is the y-coordinate. This has to be what's messed up. Let's see how f is defined:
f = linha*g;
OK, linha is the line number and it's only changed once in the loop without any conditional logic. So the problem is probably g. Let's see how that one is defined:
if (linha > 1) {
g = 150;
}
else {
g = 0;
}
Hey, g changes after the first iteration — precisely when our problem crops up. Let's see what the values of linha*g are:
1 * 0 = 0
2 * 150 = 300 (+300)
3 * 150 = 450 (+150)
4 * 150 = 600 (+150)
Ah-ha — the problem is that setting g to 0 on the first iteration breaks the pattern.