制作 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。

1 // Implement viewDidLoad to do additional setup after loading the view, typically from a nib.   2 - (void)viewDidLoad {
     3     [super viewDidLoad];   4       5     //   6     totalPages = 0;   7     currentPage = 0;   8       9     //  10     textLabel.numberOfLines = 0;  11      12     //  13     if (!text) {
    14         // 从文件里加载文本串  15         [self loadString];  16          17         // 计算文本串的大小尺寸  18         CGSize totalTextSize = [text sizeWithFont:[UIFont systemFontOfSize:FONT_SIZE_MAX]  19                                          constrainedToSize:CGSizeMake(textLabel.frame.size.width, CGFLOAT_MAX)  20                                     lineBreakMode:UILineBreakModeWordWrap];  21  22         // 如果一页就能显示完，直接显示所有文本串即可。  23         if (totalTextSize.height < textLabel.frame.size.height) {
    24             textLabel.text = text;  25         }  26         else {
    27             // 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！  28             NSUInteger textLength = [text length];  29             referTotalPages = (int)totalTextSize.height/(int)textLabel.frame.size.height+1;  30             referCharatersPerPage = textLength/referTotalPages;  31              32             // 申请最终保存页面NSRange信息的数组缓冲区  33             int maxPages = referTotalPages;  34             rangeOfPages = (NSRange *)malloc(referTotalPages*sizeof(NSRange));  35             memset(rangeOfPages, 0x0, referTotalPages*sizeof(NSRange));  36              37             // 页面索引  38             int page = 0;  39              40             for (NSUInteger location = 0; location < textLength; ) {
    41                 // 先计算临界点（尺寸刚刚超过UILabel尺寸时的文本串）  42                 NSRange range = NSMakeRange(location, referCharatersPerPage);  43                  44                 // reach end of text ?  45                 NSString *pageText;  46                 CGSize pageTextSize;  47                  48                 while (range.location + range.length < textLength) {
    49                     pageText = [text substringWithRange:range];  50                      51                     pageTextSize = [pageText sizeWithFont:[UIFont systemFontOfSize:FONT_SIZE_MAX]  52                                         constrainedToSize:CGSizeMake(textLabel.frame.size.width, CGFLOAT_MAX)  53                                             lineBreakMode:UILineBreakModeWordWrap];  54                      55                     if (pageTextSize.height > textLabel.frame.size.height) {
    56                         break;  57                     }  58                     else {
    59                         range.length += referCharatersPerPage;  60                     }  61                 }  62                  63                 if (range.location + range.length >= textLength) {
    64                     range.length = textLength - range.location;  65                 }  66                  67                 // 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  68                 while (range.length > 0) {
    69                     pageText = [text substringWithRange:range];  70                      71                     pageTextSize = [pageText sizeWithFont:[UIFont systemFontOfSize:FONT_SIZE_MAX]  72                                         constrainedToSize:CGSizeMake(textLabel.frame.size.width, CGFLOAT_MAX)  73                                             lineBreakMode:UILineBreakModeWordWrap];  74                      75                     if (pageTextSize.height <= textLabel.frame.size.height) {
    76                         range.length = [pageText length];  77                         break;  78                     }  79                     else {
    80                         range.length -= 2;  81                     }  82                 }  83                  84                 // 得到一个页面的显示范围  85                 if (page >= maxPages) {
    86                     maxPages += 10;  87                     rangeOfPages = (NSRange *)realloc(rangeOfPages, maxPages*sizeof(NSRange));  88                 }  89                 rangeOfPages[page++] = range;  90                  91                 // 更新游标  92                 location += range.length;  93             }  94  95             // 获取最终页面数量  96             totalPages = page;  97              98             // 更新UILabel内容  99             textLabel.text = [text substringWithRange:rangeOfPages[currentPage]]; 100         } 101     } 102     103     // 显示当前页面进度信息，格式为："8/100" 104     pageInfoLabel.text = [NSString stringWithFormat:@"%d/%d", currentPage+1, totalPages]; 105 }

 

1 // 上一页  2 - (IBAction)actionPrevious:(id)sender {
    3     if (currentPage > 0) {
    4         currentPage--;  5          6         NSRange range = rangeOfPages[currentPage];  7         NSString *pageText = [text substringWithRange:range];  8          9         textLabel.text = pageText; 10 11         // 12         pageInfoLabel.text = [NSString stringWithFormat:@"%d/%d", currentPage+1, totalPages]; 13     } 14 }

1 // 下一页  2 - (IBAction)actionNext:(id)sender {
    3     if (currentPage < totalPages-1) {
    4         currentPage++;  5          6         NSRange range = rangeOfPages[currentPage];  7         NSString *pageText = [text substringWithRange:range];  8          9         textLabel.text = pageText; 10         11         // 12         pageInfoLabel.text = [NSString stringWithFormat:@"%d/%d", currentPage+1, totalPages]; 13     } 14 }