如何在C#方法中实现方法的懒加载

在C#中，可以使用委托、闭包和async/await关键字来实现方法的懒加载

1. 使用委托：

using System;

public class LazyLoading
{
    private readonly Func<int, int> _multiplyByTwo;
    private int _number;

    public LazyLoading(Func<int, int> multiplyByTwo)
    {
        _multiplyByTwo = multiplyByTwo;
    }

    public int MultiplyByTwo(int input)
    {
        return _multiplyByTwo(input);
    }

    public void SetNumber(int number)
    {
        _number = number;
    }
}

class Program
{
    static void Main(string[] args)
    {
        LazyLoading lazyLoading = new LazyLoading(x => x * 2);
        Console.WriteLine(lazyLoading.MultiplyByTwo(5)); // 输出 10
        lazyLoading.SetNumber(6);
        Console.WriteLine(lazyLoading.MultiplyByTwo(6)); // 输出 12
    }
}

2. 使用闭包：

using System;

public class LazyLoading
{
    private readonly Func<int, int> _multiplyByTwo;
    private int? _number;

    public LazyLoading(Func<int, int> multiplyByTwo)
    {
        _multiplyByTwo = multiplyByTwo;
    }

    public int MultiplyByTwo(int input)
    {
        if (!_number.HasValue)
        {
            throw new InvalidOperationException("Number is not set.");
        }

        return _multiplyByTwo(_number.Value);
    }

    public void SetNumber(int number)
    {
        _number = number;
    }
}

class Program
{
    static void Main(string[] args)
    {
        LazyLoading lazyLoading = new LazyLoading(x => x * 2);
        Console.WriteLine(lazyLoading.MultiplyByTwo(5)); // 输出 10
        lazyLoading.SetNumber(6);
        Console.WriteLine(lazyLoading.MultiplyByTwo(6)); // 输出 12
    }
}

3. 使用async/await关键字：

using System;
using System.Threading.Tasks;

public class LazyLoading
{
    private readonly Func<int, Task<int>> _multiplyByTwoAsync;
    private int? _number;

    public LazyLoading(Func<int, Task<int>> multiplyByTwoAsync)
    {
        _multiplyByTwoAsync = multiplyByTwoAsync;
    }

    public async Task<int> MultiplyByTwoAsync(int input)
    {
        if (!_number.HasValue)
        {
            throw new InvalidOperationException("Number is not set.");
        }

        return await _multiplyByTwoAsync(_number.Value);
    }

    public void SetNumber(int number)
    {
        _number = number;
    }
}

class Program
{
    static async Task Main(string[] args)
    {
        LazyLoading lazyLoading = new LazyLoading(x => Task.FromResult(x * 2));
        Console.WriteLine(await lazyLoading.MultiplyByTwoAsync(5)); // 输出 10
        lazyLoading.SetNumber(6);
        Console.WriteLine(await lazyLoading.MultiplyByTwoAsync(6)); // 输出 12
    }
}

在这些示例中，我们创建了一个名为LazyLoading的类，该类具有一个委托、闭包或async/await方法，用于在需要时计算输入值的两倍。当调用MultiplyByTwo方法时，只有在首次调用时才会计算结果，从而实现懒加载。