How do I calculate the exact height of text using UIKit?

问题

I'm using -[NSString sizeWithFont] to get the text height. The character 't' is clearly taller than 'm', but -sizeWithFont returns the same height for both these strings. Here's the code:

UIFont* myFont = [UIFont fontWithName:@"Helvetica" size:1000.0];
NSString* myStr = @"m";
CGSize mySize = [myStr sizeWithFont:myFont];

With 'm' as shown, it returns {834, 1151}. With myStr = @"t" instead, it's {278, 1151}. The smaller width shows up as expected, but not the height.

Does some other function wrap the text tightly? I'm ideally looking for something equivalent to Android's Paint.getTextBounds().

回答1:

Hmmm... I assume you're only going to be working with individual characters then. sizeWithFont, as noted above, returns the height of the largest character of that font as the text field is going to be that height no matter what you do. You would be able to get the LARGEST height values (UIFont's CGFloat capHeight) however it looks like you're going to be working with all kinds of text

I would take a look at the CoreText framework. Start here and read away. Inevitably you're going to end up with something along the lines of this:

CGFloat GetLineHeightForFont(CTFontRef iFont)
{
    CGFloat lineHeight = 0.0;

    check(iFont != NULL);
    lineHeight += CTFontGetLeading(iFont);
    return lineHeight;
}

回答2:

The information you get back from this method is basically the line height for the font (i.e., it's the ascent plus the descent for the font you've chosen). It's not based on individual characters, it's based on specific font metrics. You can get most of the information about a font's metrics from the UIFont class (e.g., the method -ascender gives you the height of the ascender for the font). Mostly, you will be dealing with the total amount of vertical space needed to draw the glyphs with the heights ascenders and the lowest descenders for that font. There is no way to get information about individual glyphs from UIFont. If you need this information, you'll have to look at the CoreText framework, which gives you a lot more flexibility in how you draw and arrange glyphs but is far, far more complicated to use.

For more information on dealing with text in your app, please se the Drawing and Managing Text section of the Text, Web, and Editing Programming Guide. It is also a good launching point for most of the frameworks and classes you'll need to deal with whether you go the UIKit or the CoreText route.

来源：https://stackoverflow.com/questions/8751219/how-do-i-calculate-the-exact-height-of-text-using-uikit

标签

objective-c

ios

cocoa-touch

nsstring