- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
   
    
    //获取字符串的宽度
    NSLog(@"获得字符串的宽度:%f",[self widthForString:@"我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！" fontSize:10.0 andHeight:10.0]);
    
    //获取字符串的高度
    NSLog(@"获得字符串的宽度:%f",[self heightForString:@"我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！我爱你！" fontSize:10.0 andWidth:10.0]);
    
    
    
}

#pragma -mark -functions

//获取字符串的宽度
-(float) widthForString:(NSString *)value fontSize:(float)fontSize andHeight:(float)height
{
    CGSize sizeToFit = [value sizeWithFont:[UIFont systemFontOfSize:fontSize] constrainedToSize:CGSizeMake(CGFLOAT_MAX, height) lineBreakMode:NSLineBreakByWordWrapping];//此处的换行类型（lineBreakMode）可根据自己的实际情况进行设置
    return sizeToFit.width;
}
//获得字符串的高度
-(float) heightForString:(NSString *)value fontSize:(float)fontSize andWidth:(float)width
{
    CGSize sizeToFit = [value sizeWithFont:[UIFont systemFontOfSize:fontSize] constrainedToSize:CGSizeMake(width, CGFLOAT_MAX) lineBreakMode:NSLineBreakByCharWrapping];//此处的换行类型（lineBreakMode）可根据自己的实际情况进行设置
    return sizeToFit.height;
}

2015-10-19 13:49:21.980 获取字符串的宽度[5932:135850] 获得字符串的宽度:320.000000
2015-10-19 13:49:21.981 获取字符串的宽度[5932:135850] 获得字符串的宽度:381.760010