Question

我想在运行时和设计时运行一些注册码。对我来说，最好的方法似乎是使用静态构造函数，但它似乎没有运行。

public class MyComponent : Component 
{
    static string someVar = "Static constructor not yet run";

    static MyComponent() 
    {
        someVar = "Static constuctor run";
    }

    public MyComponent()
    {
        //Do some constructor things
    }
}

有没有办法在设计时运行静态构造函数？如果没有，是否有可以接受的模式来做这种事情？

Answer 1

是的，无论设计时间或运行时间如何，静态构造函数都将运行。一个简单的测试就可以证明这一点。

public class MyComponent : Component
{
    static string someVar = "Static constructor not yet run";

    static MyComponent()
    {
        someVar = "Static constructor run";
        MessageBox.Show(someVar);
    }

    public MyComponent()
    {
        //Do some constructor things
    }
}

现在将组件添加到设计器中，然后构建项目。您将看到带消息静态构造函数运行的消息框。

Answer 2

这就是MSDN对static constructors所说的话：

自动调用静态构造函数来初始化类   在创建第一个实例之前或任何静态成员之前   引用。

无法直接调用静态构造函数。

用户无法控制何时执行静态构造函数   该计划。

基本上，你不能像通常的方法那样通过调用代码来控制代码。

关于它们如何工作的一个例子：

    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.      
   */

使用设计器时是否会调用静态构造函数？

2 个答案: