ios - Two UILabels dynamic width in a row autolayout with Masonry

Question

I have two UILabels side by side in a row.Left label autolayout with its text and right label's width base on left label.

Code will be shown below.

UIView *preView;
NSArray *titleArray = @[@"abc",@"abcd",@"abcde",@"abcdefg"];
for (int i = 0; i < titleArray.count ; i ++) {
    UILabel *label = [[UILabel alloc] init];
    label.backgroundColor = [UIColor blueColor];
    label.font = [UIFont systemFontOfSize:15];
    label.text = titleArray[i];
    [self.view addSubview:label];

    UILabel *valueLabel = [[UILabel alloc] init];
    valueLabel.backgroundColor = [UIColor redColor];
    valueLabel.font = [UIFont systemFontOfSize:15];
    valueLabel.text = @" ";
    [self.view addSubview:valueLabel];

    preView = label;

    [label mas_makeConstraints:^(MASConstraintMaker *make) {
        if (i == 0) {
            make.top.equalTo(@50);
        }else
            make.top.equalTo(preView.mas_bottom).offset(10);
        make.left.equalTo(@10);
    }];
    [valueLabel mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(label);
        make.left.equalTo(label.mas_right).offset(10);
        make.right.equalTo(@-10);
    }];
}

It's under my expectation except row 1st. Could somebody know how to make it work?

Any help will be appreciated.