C# 方法使用汇总（GetEnumerator用法，？？用法等）

目录：

1、??运算符使用

2、GetEnumerator方法

3、ResourceManager.GetString方法获得Resources的字符。

4、获得Settings文件的字符。

一、??可能是一个被遗忘的运算符，很少看到有人用它，它的用法很简单却很实用：
variable ?? defaultValue
相当于
variable == null ? defaultValue : variable
有了它，一行便能搞定Lazy Evaluation了：
使用??之前：

public UserAccess Users
{
get
{
if (_users == null)
{
_users = Proxy.GetQueryObject<UserAccess>();
}
return _users;
}
}

之后：

public UserAccess Users
{
get
{
return _users ?? (_users = Proxy.GetQueryObject<UserAccess>());
}
}

注：这个运算符只支持引用类型和Nullable类型。

int?就是Nullable<int>，Nullable类型也支持的。

原文：/article/4991814.html

二.GetEnumerator

下面的示例说明 GetEnumerator 方法的用法。包括在枚举数为活动的情况下从基础 DataTable 中删除行时枚举数的行为。

view plaincopy to clipboardprint?
public static void Main()
{
try
{
DataTable userTable = new DataTable("peopleTable");

userTable.Columns.Add("Id", typeof(int));
userTable.Columns.Add("Name", typeof(string));

// Note that even if you create the DataTableReader
// before adding the rows, the enumerator can still
// visit all the rows.
DataTableReader reader = userTable.CreateDataReader();
userTable.Rows.Add(new object[] { 1, "Peter" });
userTable.Rows.Add(new object[] { 2, "Mary" });
userTable.Rows.Add(new object[] { 3, "Andy" });
userTable.Rows.Add(new object[] { 4, "Russ" });

IEnumerator enumerator = reader.GetEnumerator();
// Keep track of whether the row to be deleted
// has actually been deleted yet. This allows
// this sample to demonstrate that the enumerator
// is able to survive row deletion.
bool isRowDeleted = false;
while (enumerator.MoveNext())
{
DbDataRecord dataRecord = (DbDataRecord)enumerator.Current;

// While the enumerator is active, delete a row.
// This doesn't affect the behavior of the enumerator.
if (!isRowDeleted)
{
isRowDeleted = true;
userTable.Rows[2].Delete();
}
Console.WriteLine(dataRecord.GetString(1));
}
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
Console.ReadLine();

原文：http://www.cnblogs.com/suiqirui19872005/archive/2007/08/11/851752.html

2.2第二种用法

const int times =1000;

public static void Test2()
{
Stopwatch watch = new Stopwatch();
Hashtable hastable = new Hashtable();

for (int i = 0; i < 10000; i++)
{
hastable.Add(i, i.ToString() + "值");
}
//测试GetEnumerator
watch.Start();
for (int i = 0; i < times; i++)
{
IDictionaryEnumerator enumerator = hastable.GetEnumerator();
while (enumerator.MoveNext())
{
string key = enumerator.Key.ToString();
string value = enumerator.Value.ToString();
}
}
watch.Stop();
Console.WriteLine("Hashtable GetEnumerator耗时" + watch.ElapsedMilliseconds);
Console.WriteLine("---------------");

watch.Reset();
//测试ForEach
watch.Start();
for (int i = 0; i < times; i++)
{
foreach (object item in hastable.Keys)
{
string key = item.ToString();
string value = hastable[item].ToString();
}
}
watch.Stop();
Console.WriteLine("Hashtable ForEach耗时" + watch.ElapsedMilliseconds);
Console.WriteLine("---------------");

watch.Reset();
Dictionary<int, string> dictionary = new Dictionary<int, string>();
for (int i = 0; i < 10000; i++)
{
dictionary.Add(i, i.ToString() + "值");
}
watch.Start();
for (int i = 0; i < times; i++)
{
Dictionary<int,string>.Enumerator enumerator = dictionary.GetEnumerator();
while (enumerator.MoveNext())
{
int key = enumerator.Current.Key;
string value = enumerator.Current.Value;
}
}
watch.Stop();
Console.WriteLine("Dictionary GetEnumerator耗时" + watch.ElapsedMilliseconds);
Console.WriteLine("---------------");

watch.Reset();
//测试ForEach
watch.Start();
for (int i = 0; i < times; i++)
{
foreach (int item in dictionary.Keys)
{
int key = item;
string value = dictionary[item];
}
}
watch.Stop();
Console.WriteLine("Dictionary ForEach耗时" + watch.ElapsedMilliseconds);
Console.WriteLine("---------------");
Console.ReadKey();
}
}

　　原文：/article/4717697.html

三、获得Resources的字符。通过ResourceManager.GetString方法获得定义在Properties.Resources的String字符。 WpfApplicationSomeMethodTest.Properties.Resources.ResourceManager.GetString("TestString");

四、获得Settings文件的字符。WpfApplicationSomeMethodTest.Properties.Settings.Default.DefaultFolder;