Question

我正试图从列表中获取一些值。但我想确保如果密钥不存在，它将返回默认值0而不是抛出异常。

var businessDays = days.Where(x => x.Year == year).ToDictionary(x => x.Month, x => x.Qty);

var vmBusinessDays = new BusinessDay()
{
    Jan = businessDays[1],
    Feb = businessDays[2],
    Mar = businessDays[3],
    Apr = businessDays[4],
    May = businessDays[5]
    [..]
};

如何在不污染代码的情况下使用Nullable<T>.GetValueOrDefault或null-coalescing之类的内容？

var vmBusinessDays = new BusinessDay()
{
    Jan = businessDays[1].GetValueOrDefault(),
    Feb = businessDays[1]?? 0
}

我知道Dictionary<TKey, TValue>.TryGetValue，但它会重复代码行，以便为每个属性设置输出值。

Answer 1

您可以定义自己的扩展方法：

public static class DictionaryExtensions
{
    public static TValue GetValueOrDefault<TKey, TValue>(
        this IDictionary<TKey, TValue> dict, TKey key)
    {
        TValue val;
        if (dict.TryGetValue(key, out val))
            return val;
        return default(TValue);
    }
}

然后您可以这样使用它：

var vmBusinessDays = new BusinessDay()
{
    Jan = businessDays.GetValueOrDefault(1),
    Feb = businessDays.GetValueOrDefault(2)
}

对于Dicitionary或List，GetValueOrDefault或null-coalescing

1 个答案: