Get truncated text from UILabel

问题:

Is there anyway I can get the truncated version of the text for a UILabel?

In short, I have a paragraph of text, and two UILabels - label A, which is 2 lines long, and label B, which is a variable height. Label A is above label B. The idea is that label A shows the first two lines of the paragraph of text, and upon a certain user action, label B because visible and displays the rest of the text.

I'm having trouble determining what should go in label B, as I don't know what's being shown in label A. I'd need to also remove the "..." from label A.

Note: I realize this is a bit convoluted but there are some good reasons for it, which I won't clutter up the question with.

回答1:

I wonder if you could use the methods in the NSString UIKit Additions to figure out how much fits into label A.

A crude way might be to start with the first character of your text and test for the size it would take up (-sizeWithFont:forWidth:lineBreakMode: maybe?) and then keep adding characters one at a time until it doesn't fit into your label A any more.

I hope somebody else can come up with a better way to do this, but the above should work.

Update

Last night I looked a bit into Core Text for my own app and came across CTFramesetterSuggestFrameSizeWithConstraints. You could maybe use this to figure out how much of your string fits into the label, by looking at the fitRange in that function.

Update 2:

I think this should work, but I have just typed this in here, so it may not even compile:

UIFont *uiFont = [UIFont systemFontOfZise:13.0f]; // whichever font you're using
CTFontRef ctFont = CTFontCreateWithName((CFStringRef)uiFont.fontName, uiFont.pointSize, NULL);
NSDictionary *attr = [NSDictionary dictionaryWithObject:(id)ctFont forKey:(id)kCTFontAttributeName];
CFRelease(ctfont);
NSAttributedString *attrString  = [[NSAttributedString alloc] initWithString:yourLabelText attributes:attr];
CTFrameSetterRef frameSetter = CTFrameSetterCreateWithAttributedString((CFAttributedStringRef)attrString);
[attrString release];
CFRange fitRange;
CTFrameSetterSuggestFrameSizeWithConstrains(
    frameSetter,
    CFRangeMake(0, 0),
    NULL,
    CGSizeMake(labelWidth, labelHeight),
    &fitRange);
CFRelease(frameSetter);
CFIndex numberOfCharactersThatFit = fitRange.length;

回答2:

thanks to Thomas Müller be sure to set line break mode the myLabel to this:

myLabel.lineBreakMode = NSLineBreakByWordWrapping;

by this method you can get chunked strings that actually fit in the constrained size. Here is the baked code:

- (NSArray *)truncate:(NSString *)text
{
    NSMutableArray *textChunks = [[NSMutableArray alloc] init];

    NSString *chunk = [[NSString alloc] init];

    CTFramesetterRef frameSetter;
    UIFont *uiFont = [UIFont systemFontOfSize:17.0f];
    CTFontRef ctFont = CTFontCreateWithName((__bridge CFStringRef)uiFont.fontName, uiFont.pointSize, NULL);
    NSDictionary *attr = [NSDictionary dictionaryWithObject:(__bridge id)ctFont forKey:(id)kCTFontAttributeName];
    NSMutableAttributedString *attrString  = [[NSMutableAttributedString alloc] initWithString:text attributes:attr];

    CFRange fitRange;
    while (attrString.length>0) {

        frameSetter = CTFramesetterCreateWithAttributedString ((__bridge CFAttributedStringRef) attrString);
            CTFramesetterSuggestFrameSizeWithConstraints(frameSetter, CFRangeMake(0,0), NULL, CGSizeMake(myLabel.frame.size.width, myLabel.frame.size.height), &fitRange);
        CFRelease(frameSetter);

       chunk = [[attrString attributedSubstringFromRange:NSMakeRange(0, fitRange.length)] string];

        [textChunks addObject:chunk];

        [attrString setAttributedString: [attrString attributedSubstringFromRange:NSMakeRange(fitRange.length, attrString.string.length-fitRange.length)]];

    }


    return textChunks;
}

回答3:

For Label A, calculate approximate character that should fit perfectly for two lines, for the particular font you are using.

For label B, set variable Height that the whole text must fit into it.