作 iPhone 电子书时，如果把大段文字放在 UITextView 或 UILabel里显示，是不能分页的，阅读时就像再看一大卷滚不到头的纸带，用户体验很差。下面这段代码可以实现 UILabel尺寸固定，根据文本内容和字体动态分页显示，电子书方面的应用应该非常有用。

// Implement viewDidLoad to do additional setup after loadingthe view, typically from a nib.
- (void)viewDidLoad {
    [superviewDidLoad];
    
    //
    totalPages= 0;
    currentPage= 0;
    
    //
    textLabel.numberOfLines= 0;
    
    //
    if(!text) {
        //从文件里加载文本串
        [selfloadString];
        
        //计算文本串的大小尺寸
        CGSizetotalTextSize = [text sizeWithFont:[UIFontsystemFontOfSize:FONT_SIZE_MAX]
                                        constrainedToSize:CGSizeMake(textLabel.frame.size.width,CGFLOAT_MAX)
                                    lineBreakMode:UILineBreakModeWordWrap];

//如果一页就能显示完，直接显示所有文本串即可。
        if(totalTextSize.height < textLabel.frame.size.height){
            textLabel.text= text;
        }
        else{
            //计算理想状态下的页面数量和每页所显示的字符数量，只是拿来作为参考值用而已！
            NSUIntegertextLength = [text length];
            referTotalPages=(int)totalTextSize.height/(int)textLabel.frame.size.height+1;
            referCharatersPerPage= textLength/referTotalPages;
            
            //申请最终保存页面NSRange信息的数组缓冲区
            intmaxPages = referTotalPages;
            rangeOfPages= (NSRange *)malloc(referTotalPages*sizeof(NSRange));
            memset(rangeOfPages,0x0, referTotalPages*sizeof(NSRange));
            
            //页面索引
            intpage = 0;
            
            for(NSUInteger location = 0; location < textLength; ){
                //先计算临界点（尺寸刚刚超过UILabel尺寸时的文本串）
                NSRangerange = NSMakeRange(location, referCharatersPerPage);
                
                //reach end of text ?
                NSString*pageText;
                CGSizepageTextSize;
                
                while(range.location + range.length < textLength) {
                    pageText= [text substringWithRange:range];
                    
                    pageTextSize= [pageText sizeWithFont:[UIFontsystemFontOfSize:FONT_SIZE_MAX]
                                        constrainedToSize:CGSizeMake(textLabel.frame.size.width,CGFLOAT_MAX)
                                            lineBreakMode:UILineBreakModeWordWrap];
                    
                    if(pageTextSize.height > textLabel.frame.size.height){
                        break;
                    }
                    else{
                        range.length+= referCharatersPerPage;
                    }
                }
                
                if(range.location + range.length >= textLength){
                    range.length= textLength - range.location;
                }
                
                //然后一个个缩短字符串的长度，当缩短后的字符串尺寸小于textLabel的尺寸时即为满足
                while(range.length > 0) {
                    pageText= [text substringWithRange:range];
                    
                    pageTextSize= [pageText sizeWithFont:[UIFontsystemFontOfSize:FONT_SIZE_MAX]
                                        constrainedToSize:CGSizeMake(textLabel.frame.size.width,CGFLOAT_MAX)
                                            lineBreakMode:UILineBreakModeWordWrap];
                    
                    if(pageTextSize.height <= textLabel.frame.size.height){
                        range.length= [pageText length];
                        break;
                    }
                    else{
                        range.length-= 2;
                    }
                }
                
                //得到一个页面的显示范围
                if(page >= maxPages) {
                    maxPages+= 10;
                    rangeOfPages= (NSRange *)realloc(rangeOfPages, maxPages*sizeof(NSRange));
                }
                rangeOfPages[page++]= range;
                
                //更新游标
                location+= range.length;
            }

//获取最终页面数量
            totalPages= page;
            
            //更新UILabel内容
            textLabel.text= [text substringWithRange:rangeOfPages[currentPage]];
        }
    }
    
    //显示当前页面进度信息，格式为："8/100"
    pageInfoLabel.text= [NSString stringWithFormat:@"%d/%d", currentPage+1,totalPages];
}

////////////////////////////////////////////////////////////////////////////////////////
// 上一页
- (IBAction)actionPrevious:(id)sender {
    if(currentPage > 0) {
        currentPage--;
        
        NSRangerange = rangeOfPages[currentPage];
        NSString*pageText = [text substringWithRange:range];
        
        textLabel.text= pageText;

//
        pageInfoLabel.text= [NSString stringWithFormat:@"%d/%d", currentPage+1,totalPages];
    }
}

////////////////////////////////////////////////////////////////////////////////////////
// 下一页
- (IBAction)actionNext:(id)sender {
    if(currentPage < totalPages-1) {
        currentPage++;
        
        NSRangerange = rangeOfPages[currentPage];
        NSString*pageText = [text substringWithRange:range];
        
        textLabel.text= pageText;
        
        //
        pageInfoLabel.text= [NSString stringWithFormat:@"%d/%d", currentPage+1,totalPages];
    }
}