xcode UILabel分页计算

-(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];
	
	//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,现在还给它
			
		}
		
		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];
}