自用的动态获取UIlabel的Size的方法

+ (CGSize) getLabelSizeBy:(UILabel *) label andContent:(NSString *) content andMaxLabelWidth:(CGFloat) maxWidth {
    NSString * text = label.text;
    if([FMUtils isStringEmpty:content]) {
        return CGSizeZero;
    }
    [label setText:content];
    CGSize resultSize = [label sizeThatFits:CGSizeMake(maxWidth, MAXFLOAT)];
    [label setText:text];
    return resultSize;
}