怎样在C#中实现方法的懒加载

在C#中，可以使用委托、事件或异步方法来实现方法的懒加载。下面是使用这三种方法的示例：

1. 使用委托：

using System;

public class LazyMethod
{
    private readonly Func<object, object> _lazyMethod;
    private object _result;

    public LazyMethod(Func<object, object> lazyMethod)
    {
        _lazyMethod = lazyMethod;
    }

    public object Execute(object input)
    {
        if (_result == null)
        {
            _result = _lazyMethod(input);
        }

        return _result;
    }
}

class Program
{
    static void Main(string[] args)
    {
        var lazyMethod = new LazyMethod(x =>
        {
            Console.WriteLine("Method is being executed.");
            return x * 2;
        });

        var result = lazyMethod.Execute(5);
        Console.WriteLine($"Result: {result}");
    }
}

2. 使用事件：

using System;

public class LazyMethod
{
    private readonly EventHandler _eventHandler;
    private bool _isExecuted = false;

    public LazyMethod(EventHandler eventHandler)
    {
        _eventHandler = eventHandler;
    }

    public void Execute()
    {
        if (!_isExecuted)
        {
            _eventHandler?.Invoke(this, EventArgs.Empty);
            _isExecuted = true;
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        var lazyMethod = new LazyMethod(x =>
        {
            Console.WriteLine("Method is being executed.");
            return x * 2;
        });

        lazyMethod.Execute();
        Console.WriteLine("Result: Method executed.");
    }
}

3. 使用异步方法：

using System;
using System.Threading.Tasks;

public class LazyMethod
{
    private readonly Func<Task<object>> _asyncLazyMethod;
    private Task<object> _task;

    public LazyMethod(Func<Task<object>> asyncLazyMethod)
    {
        _asyncLazyMethod = asyncLazyMethod;
    }

    public async Task<object> ExecuteAsync()
    {
        if (_task == null)
        {
            _task = _asyncLazyMethod();
            await _task;
        }

        return _task.Result;
    }
}

class Program
{
    static async Task Main(string[] args)
    {
        var lazyMethod = new LazyMethod(async () =>
        {
            Console.WriteLine("Method is being executed.");
            await Task.Delay(1000);
            return "Result";
        });

        var result = await lazyMethod.ExecuteAsync();
        Console.WriteLine($"Result: {result}");
    }
}

这些示例展示了如何在C#中实现方法的懒加载。你可以根据具体需求选择合适的方法。