如何将旧数据类型值与新数据类型值进行比较

Question

所以我正在使用这个API，它显示了以太币的当前价格和其他信息。我正在尝试创建一个小型控制台应用程序，用于检查该值是否与我们上次扫描时相比发生了变化。

到目前为止，我所拥有的是......而且我知道我正在用当前值扫描当前值，所以很明显它永远不会改变。 我尝试设置一个变量来保存旧值，但没有做任何事情。

如何比较第一次扫描和第二次扫描以查看浮点值是上升还是下降？

private static void Ticker()
        {
            while (true)
            {
                const string uri = @"https://api.coinmarketcap.com/v1/ticker/ethereum/";
                var client = new WebClient();
                var content = client.DownloadString(uri);

                var results = JsonConvert.DeserializeObject<List<CoinApi>>(content);

                float currentAmount = results[0].price_usd;
                if (currentAmount < currentAmount)
                {
                    Console.WriteLine("Ammount is lower than the last time.");
                }
                else if (currentAmount > currentAmount)
                {
                    Console.WriteLine("The amount is higher than the last time.");
                }
                else if (currentAmount == currentAmount)
                {
                    Console.WriteLine("The amount hasnt changed since the last time we scanned.");
                }
            }
        }

这是类文件。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CryptoTicker.Core
{
    class Main
    {
    }

    public class CoinApi
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public string Symbol { get; set; }
        public float price_usd { get; set; }
    }
}

Answer 1

尝试将旧值保存到静态变量应该可以解决您的问题。 TODOS：你将如何处理你的第一个请求？处理异常等...

其他问题：是否应该在 while(true) 中运行？也许您应该使用 HttpClient 并重用它。

    private static float _oldValue;

    private static void Ticker()
    {
        while (true)
        {
            const string uri = @"https://api.coinmarketcap.com/v1/ticker/ethereum/";
            var client = new WebClient();
            var content = client.DownloadString(uri);

            var results = JsonConvert.DeserializeObject<List<CoinApi>>(content);

            float currentAmount = results[0].price_usd;
            if (currentAmount < _oldValue)
            {
                Console.WriteLine("Ammount is lower than the last time.");
            }
            else if (currentAmount > _oldValue)
            {
                Console.WriteLine("The amount is higher than the last time.");
            }
            else if (currentAmount == _oldValue)
            {
                Console.WriteLine("The amount hasnt changed since the last time we scanned.");
            }

            _oldValue = currentAmount;
        }
    }

Answer 2

正如你所写，currentAmount 将永远等于它自己。

这应该可行：

private static void Ticker()
{
    float previousAmount = 0.0;
    while (true)
    {
        const string uri = @"https://api.coinmarketcap.com/v1/ticker/ethereum/";
        var client = new WebClient();
        var content = client.DownloadString(uri);

        var results = JsonConvert.DeserializeObject<List<CoinApi>>(content);

        float currentAmount = results[0].price_usd;

        if (currentAmount < previousAmount )
        {
            Console.WriteLine("Ammount is lower than the last time.");
        }
        else if (currentAmount > previousAmount )
        {
            Console.WriteLine("The amount is higher than the last time.");
        }
        else if (currentAmount == previousAmount)
        {
            Console.WriteLine("The amount hasnt changed since the last time we scanned.");
        }
        previousAmount = currentAmount;
    }
}

Answer 3

您需要记住之前的值。一种方法是维护 id 和 CoinApi 类的字典

public Dictionary<int, CoinApi> CoinDict = new Dictionary<int, CoinAPI>();

然后您可以将当前值存储在此字典中，然后将新值与现有值进行比较。然后更新为新值

public void UpdateCoinDict(CoinApi coin)
{
    CoinDict[coin.Id] = coin;
}

public float GetCoinPrice(CoinApi coin)
{
    if (CoinDict.Contains(coin.Id))
    {
        return CoinDict[coin.Id].price_usd;
    }
    else 
    {
        UpdateCoinDict(coin);
        return coin.price_usd;
    }              
}



private static void Ticker()
{
    while (true)
    {
        const string uri = @"https://api.coinmarketcap.com/v1/ticker/ethereum/";
        var client = new WebClient();
        var content = client.DownloadString(uri);

        var results = JsonConvert.DeserializeObject<List<CoinApi>>(content);

        for (coin in results)
        {
            float currentAmount = coin.price_usd;
            float oldPrice = GetCoinPrice(coin); 
            if (currentAmount < oldPrice)
            {
                Console.WriteLine("Ammount is lower than the last time.");
            }
            else if (currentAmount > oldPrice)
            {
                Console.WriteLine("The amount is higher than the last time.");
            }
            else
            {
            Console.WriteLine("The amount hasnt changed since the last time we scanned.");
            }
        } 
    }
}

Answer 4

您必须将先前的执行值传递给当前执行进行比较。 将该变量声明为该类中的全局分数。或者将其声明到您想要使用它的级别。