基本介紹
- 中文名:C#靜態構造函式
- 概述 :靜態構造函式是C#的一個新特性
- 簡介:靜態構造函式用於初始
- 正文:class SimpleClass
簡介,正文,注意事項,示例,
簡介
正文
class SimpleClass
{
// Static variable that must be initialized at run time.
static readonly long baseline;
// Static constructor is called at most one time, before any
// instance constructor is invoked or member is accessed.
static SimpleClass()
{
baseline = DateTime.Now.Ticks;
}
}
注意事項
--因為是.NET調用的,所以像public和private等修飾符就沒有意義了。
2、在創建第一個類實例或任何靜態成員被引用時,.NET將自動調用靜態構造函式來初始化類。
--也就是說我們無法直接調用靜態構造函式,也不可能知道靜態構造函式何時會被調用。
3、一個類只能有一個靜態構造函式。
4、無參數的構造函式可以與靜態構造函式共存。
--儘管參數列表相同,但一個屬於類,一個屬於實例,所以不會衝突。
5、最多只運行一次。
6、靜態構造函式不可以被繼承。
8、如果靜態構造函式引發異常,運行時將不會再次調用該構造函式,並且在程式運行所在的應用程式域的生存期內,類型將保持未初始化。
示例
在此示例中,類 Bus 有一個靜態構造函式。 創建 Bus 的第一個實例(bus1)時,將調用該靜態構造函式來初始化該類。 輸出示例驗證了即使創建 Bus 的兩個實例,該靜態構造函式也僅運行一次,並且在實例構造函式運行之前運行
public class Bus
{
// Static variable used by all Bus instances.
// Represents the time the first bus of the day starts its route.
protected static readonly DateTime globalStartTime;
// Property for the number of each bus.
protected int RouteNumber { get; set; }
// Static constructor to initialize the static variable.
// It is invoked before the first instance constructor is run.
static Bus()
{
globalStartTime = DateTime.Now;
// The following statement produces the first line of output,
// and the line occurs only once.
Console.WriteLine("Static constructor sets global start time to {0}",
globalStartTime.ToLongTimeString());
}
// Instance constructor.
public Bus(int routeNum)
{
RouteNumber = routeNum;
Console.WriteLine("Bus #{0} is created.", RouteNumber);
}
// Instance method.
public void Drive()
{
TimeSpan elapsedTime = DateTime.Now - globalStartTime;
// For demonstration purposes we treat milliseconds as minutes to simulate
// actual bus times. Do not do this in your actual bus schedule program!
Console.WriteLine("{0} is starting its route {1:N2} minutes after global start time {2}.",
this.RouteNumber,
elapsedTime.TotalMilliseconds,
globalStartTime.ToShortTimeString());
}
}
class TestBus
{
static void Main()
{
// The creation of this instance activates the static constructor.
Bus bus1 = new Bus(71);
// Create a second bus.
Bus bus2 = new Bus(72);
// Send bus1 on its way.
bus1.Drive();
// Wait for bus2 to warm up.
System.Threading.Thread.Sleep(25);
// Send bus2 on its way.
bus2.Drive();
// Keep the console window open in debug mode.
System.Console.WriteLine("Press any key to exit.");
System.Console.ReadKey();
}
}
/* Sample output:
Static constructor sets global start time to 3:57:08 PM.
Bus #71 is created.
Bus #72 is created.
71 is starting its route 6.00 minutes after global start time 3:57 PM.
72 is starting its route 31.00 minutes after global start time 3:57 PM.
*/