将一组按钮放在屏幕中央

Question

I'm creating an iphone app and I need to center a variable (1 to 3) number of buttons on the screen. I'd like each button to have a margin of 20.0f between them, and not have them spaced out equally. I made a pretty picture below to demonstrate what I'm talking about.

I'm having the hardest time getting this to work.

Things of note:

int btnWidth = 50;
int margin = 20;

I have constants kScreenWidth and kScreenHeight setup for the screen dimensions.

I'm creating the buttons like normal inside a loop, but the math for the x position of each button is eluding me.

for (UIButton *btn in _someArray) {
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    int x = ??????????;
    button.frame = CGRectMake( x, (kScreenHeight * 0.75f), 50.0, 30.0);
    [self.controller.currentView addSubview:button];
}

Any help with this would be greatly appreciated. Also, thanks in advance.

Answer 1

Lets say you need three buttons in center, then following is the process to achieve the x coordinate of each of 3 buttons.

//Define these globally somewhere
CGSize buttonSize = CGSizeMake(50,50);
int numOfButtons = 3; //num of buttons horizontally in one line. this will be 2 for 2nd and 1 for the third line as per your reference screen.
CGFloat maxSeparationBwButtons = 20.0f; //your horizontal margin b/w buttons
CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;

CGFloat totalLengthWithOffsets = buttonSize.width*(CGFloat)numOfButtons+(maxSeparationBwButtons)*((CGFloat)(numOfButtons+1));
CGFloat originatingX = (screenWidth - totalLengthWithOffsets)/2.0f;
//global definition ends...

//Now you can use this method to get the desired button's x coordinate
//Note : in 3 buttons the 1st button starts at position 0 and the last at 2 (aka n-1)
-(CGFloat)getXForButtonAtPosition:(int)position
{
  return (originatingX + maxSeparationBwButtons + (buttonSize.width+maxSeparationBwButtons)*(CGFloat)position);
}

In the above, you can change the values of numOfButtons, buttonSize and maxSeparationBwButtons to your desired values.