[多选项（4或者更多），自动布局]

op.m

        UIImageView *lastIV = nil;
        self.ivArrM = [NSMutableArray array];
        for (NSInteger i = 0; i < 4; i++) {
            UIImageView *iv = [[UIImageView alloc] init];
            [self addSubview:iv];
            [iv mas_makeConstraints:^(MASConstraintMaker *make) {
                if (isPad) {
                    make.width.mas_equalTo(163);
                }else{
                    make.width.equalTo(self).multipliedBy(0.5).offset(-IVMragin16 * 1.5);
                }
                make.height.equalTo(iv.mas_width).multipliedBy(0.6);
                
                if (lastIV) {
                    if (i%2 == 0) {
                        make.left.equalTo(self).offset(IVMragin16);
                        make.top.equalTo(lastIV.mas_bottom).offset(IVMragin16);
                    }else{
                        make.left.equalTo(lastIV.mas_right).offset(IVMragin16);
                        make.top.equalTo(lastIV);
                    }
                    
                }else{
                    make.left.equalTo(self).offset(IVMragin16);
                    make.top.equalTo(index.mas_bottom).offset(20);
                }
            }];
            lastIV = iv;
            [self.ivArrM addObject:iv];
        }