Draw centered text using core graphics (mobile device)

问题

I'm using this code:

CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat screenWidth = screenRect.size.width;
CGFloat screenHeight = screenRect.size.height;
NSString * text = @"text";
CGContextSetFillColorWithColor(context, [UIColor colorWithRed:1 green:1 blue:1 alpha:RETICLE_ALPHA].CGColor);
[text drawAtPoint:CGPointMake(screenWidth/2, screenHeight/2) withFont: [UIFont systemFontOfSize:22.0]];

to create a centered "text" for iOS.

But I'm not sure how to edit the code above to really get the center alignment working, because till now the text is not really centered at all.

Sorry, for the kind of stupid question but I didn't found an working example for the problem & I'm new in using Core Graphics.

回答1:

Your text is not centered because you have to subtract the text width from the screen size and then you have to divide by 2. Below I have tried to correct your code.

CGRect screenRect = [[UIScreen mainScreen] bounds];
CGFloat screenWidth = screenRect.size.width;
CGFloat screenHeight = screenRect.size.height;
NSString * text = @"text";

CGFloat minHeight = 40;
float widthIs = [text boundingRectWithSize:CGSizeMake(CGFLOAT_MAX, minHeight) options:NSStringDrawingUsesLineFragmentOrigin
 attributes:@{ NSFontAttributeName:[UIFont systemFontOfSize:22.0] }
 context:nil].size.width;
CGContextSetFillColorWithColor(context, [UIColor colorWithRed:1 green:1 blue:1 alpha:1].CGColor);
[text drawAtPoint:CGPointMake((screenWidth - widthIs)/2, (screenHeight - minHeight)/2) withFont: [UIFont systemFontOfSize:22.0]];

来源：https://stackoverflow.com/questions/48034940/draw-centered-text-using-core-graphics-mobile-device

标签

ios

objective-c

core-graphics