计算文字的尺寸(单行)
NSDictionary *btAtt = @{NSFontAttributeName : [UIFont systemFontOfSize:KCHANGEHEIGHTVALUE(14)]};
CGSize btSize = [_messageList.bt sizeWithAttributes:btAtt];
计算文字的尺寸(多行)
NSDictionary *btAtt = @{NSFontAttributeName : [UIFont systemFontOfSize:KCHANGEHEIGHTVALUE(14)]};
/**
限制文本宽高
@param 300 最大宽度
@param MAXFLOAT 高度不限
@return CGSize
*/
CGSize textSize = CGSizeMake(300, MAXFLOAT);
CGRect textRect = [_messageList.bt boundingRectWithSize:textSize options:NSStringDrawingUsesLineFragmentOrigin attributes:btAtt context:nil];
