超长字符串分页
From:http://b.imi.im/?p=388
-(NSArray*)getPagesOfString:(NSString *)cache withFont:(UIFont*)font inRect:(CGRect)r{
//返回一个数组, 包含每一页的字符串开始点和长度(NSRange)
NSMutableArray *ranges=[NSMutableArray array];
//断行类型
UILineBreakMode lineBreakMode=UILineBreakModeCharacterWrap;
//显示字体的行高
CGFloat lineHeight=[@"Sample样本" sizeWithFont:font].height;
NSInteger maxLine=floor(r.size.height/lineHeight);
NSInteger totalLines=0;
NSLog(@”Max Line Per Page: %d (%.2f/%.2f)”,maxLine,r.size.height,lineHeight);
NSString *lastParaLeft=nil;
NSRange range=NSMakeRange(0, 0);
//把字符串按段落分开, 提高解析效率
NSArray *paragraphs=[cache componentsSeparatedByString:@"/n"];
for (int p=0;p< [paragraphs count];p++) {
NSString *para;
if (lastParaLeft!=nil) {
//上一页完成后剩下的内容继续计算
para=lastParaLeft;
lastParaLeft=nil;
}else {
para=[paragraphs objectAtIndex:p];
if (p<[paragraphs count]-1)
para=[para stringByAppendingString:@"/n"]; //刚才分段去掉了一个换行,现在换给它
}
CGSize paraSize=[para sizeWithFont:font
constrainedToSize:r.size
lineBreakMode:lineBreakMode];
NSInteger paraLines=floor(paraSize.height/lineHeight);
if (totalLines+paraLines<maxLine) {
totalLines+=paraLines;
range.length+=[para length];
if (p==[paragraphs count]-1) {
//到了文章的结尾 这一页也算
[ranges addObject:[NSValue valueWithRange:range]];
//IMILog(@”===========Page Over=============”);
}
}else if (totalLines+paraLines==maxLine) {
//很幸运, 刚好一段结束,本页也结束, 有这个判断会提高一定的效率
range.length+=[para length];
[ranges addObject:[NSValue valueWithRange:range]];
range.location+=range.length;
range.length=0;
totalLines=0;
//IMILog(@”===========Page Over=============”);
}else{
//重头戏, 页结束时候本段文字 还有剩余
NSInteger lineLeft=maxLine-totalLines;
CGSize tmpSize;
NSInteger i;
for (i=1; i<[para length]; i++) {
//逐字判断是否达到了本页最大容量
NSString *tmp=[para substringToIndex:i];
tmpSize=[tmp sizeWithFont:font
constrainedToSize:r.size
lineBreakMode:lineBreakMode];
int nowLine=floor(tmpSize.height/lineHeight);
if (lineLeft<nowLine) {
//超出容量,跳出, 字符要回退一个, 应为当前字符已经超出范围了
lastParaLeft=[para substringFromIndex:i-1];
break;
}
}
range.length+=i-1;
[ranges addObject:[NSValue valueWithRange:range]];
range.location+=range.length;
range.length=0;
totalLines=0;
p–;
//IMILog(@”===========Page Over=============”);
}
}
return [NSArray arrayWithArray:ranges];
}