将任何字符串转换为类型Int32

// Calls the underlying int.TryParse method to convert a string
// representation of a number to its 32-bit signed integer equivalent.
// Returns Zero if conversion fails. 
public static int ToInt32(this string s)
{
    int retInt;
    int.TryParse(s, out retInt);
    return retInt;
}

示例使用: 字符串s = "999"; int i = s.ToInt32();

这是另一双我觉得用不完的鞋:

public static T ObjectWithMin<T, TResult>(this IEnumerable<T> sequence, Func<T, TResult> predicate)
    where T : class
    where TResult : IComparable
{
    if (!sequence.Any()) return null;

    //get the first object with its predicate value
    var seed = sequence.Select(x => new {Object = x, Value = predicate(x)}).FirstOrDefault();
    //compare against all others, replacing the accumulator with the lesser value
    //tie goes to first object found
    return
        sequence.Select(x => new {Object = x, Value = predicate(x)})
            .Aggregate(seed,(acc, x) => acc.Value.CompareTo(x.Value) <= 0 ? acc : x).Object;
}

public static T ObjectWithMax<T, TResult>(this IEnumerable<T> sequence, Func<T, TResult> predicate)
    where T : class
    where TResult : IComparable
{
    if (!sequence.Any()) return null;

    //get the first object with its predicate value
    var seed = sequence.Select(x => new {Object = x, Value = predicate(x)}).FirstOrDefault();
    //compare against all others, replacing the accumulator with the greater value
    //tie goes to last object found
    return
        sequence.Select(x => new {Object = x, Value = predicate(x)})
            .Aggregate(seed, (acc, x) => acc.Value.CompareTo(x.Value) > 0 ? acc : x).Object;
}

用法:

var myObject = myList.ObjectWithMin(x=>x.PropA);

这些方法基本上取代了像

var myObject = myList.OrderBy(x=>x.PropA).FirstOrDefault(); //O(nlog(n)) and unstable

and

var myObject = myList.Where(x=>x.PropA == myList.Min(x=>x.PropA)).FirstOrDefault(); //O(N^2) but stable

and

var minValue = myList.Min(x=>x.PropA);
var myObject = myList.Where(x=>x.PropA == minValue).FirstOrDefault(); //not a one-liner, and though linear and stable it's slower (evaluates the enumerable twice)

轻松序列化对象为XML:

public static string ToXml<T>(this T obj) where T : class
{
    XmlSerializer s = new XmlSerializer(obj.GetType());
    using (StringWriter writer = new StringWriter())
    {
        s.Serialize(writer, obj);
        return writer.ToString();
    }
}

"<root><child>foo</child</root>".ToXml<MyCustomType>();

有几次我发现自己想要Groovy的“安全导航”之类的东西。

从http://groovy.codehaus.org/Statements:

如果你在行走一个复杂的物体 图和不想要的 你可以抛出nullpointerexception 使用?。操作员而不是。来 执行导航。 Def foo = null Def bar = .myMethod()断言条 = =零

那么，您认为为它添加扩展方法是一个好主意吗? 喜欢的东西:

obj.SafelyNavigate(x => x.SomeProperty.MaybeAMethod().AnotherProperty);

我认为即使它也会带来一些麻烦，这也很好。

如果你认为这是个好主意:

您认为值类型应该发生什么?， 返回默认吗?扔吗?，通过泛型约束禁用它? 吞咽NullReferenceException来实现它会太冒险吗?， 你有什么建议?， 遍历表达式树执行每个调用或成员访问似乎很困难，而且有点过度(如果可能的话)，不是吗?

也许这只是一个坏主意:D，但我认为如果做得对，它是有用的。 如果没有类似的东西，你认为它有一些价值，我可能会给它一个机会，然后编辑答案。

日期时间扩展

例子:

DateTime firstDayOfMonth = DateTime.Now.First();
DateTime lastdayOfMonth = DateTime.Now.Last();
DateTime lastFridayInMonth = DateTime.Now.Last(DayOfWeek.Friday);
DateTime nextFriday = DateTime.Now.Next(DayOfWeek.Friday);
DateTime lunchTime = DateTime.Now.SetTime(11, 30);
DateTime noonOnFriday = DateTime.Now.Next(DayOfWeek.Friday).Noon();
DateTime secondMondayOfMonth = DateTime.Now.First(DayOfWeek.Monday).Next(DayOfWeek.Monday).Midnight();

如果你需要检查字符串的Is All char为0:

 static public bool   IsAllZero            (this string input)
        {
            if(string.IsNullOrEmpty(input))
                return true;
            foreach (char ch in input)
            {
                if(ch != '0')
                    return false;
            }
            return true;
        }