C#程式優化紀錄

2019-02-15

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C#
2022-11-28

C#程式碼優化紀錄(不定期更新)

一：運用StringBuilder類別

使用StringBuilder來做字串的連結及使用

using System.Text;

const string theShowStr = "Show Str";

StringBuilder theResultBuilder = new StringBuilder();

theResultBuilder.AppendFormat("Show : {0}",theShowStr);

theResultBuilder.AppendLine(theShowStr);

theResultBuilder.Append(theShowStr);

Response.Write(theResultBuilder.ToString());

也可使用Insert 和 Remove來使用

二：運用Dictionary<TKey,TValue>

使用Dictionary查找資料

using System.Collections.Generic;

Dictionary<string, string> theResultDict = new Dictionary<string, string>()
{
{"1", "First"},
{"2", "Second"},
{"3", "Third"},
{"4", "Fourth"},
};

var theEnum = theResultDict.GetEnumerator();
while (theEnum.MoveNext())
{
theResultBuilder.AppendFormat("Key:{0}, Value : {1}", theEnum.Current.Key, theEnum.Current.Value);
}

Response.Write(theResultBuilder.ToString());

三：字串檢查

字串值使用string.IsNullOrEmpty(string) 來檢查

四：避免在迴圈裡宣告變數
C#程式開發要遵循的一個基本原則就是避免不必要的物件建立

//避免
for(int i = 0 ; i < 5 ; ++i){
Class theClass = new Class();
}
//使用
Class theClass＝null;
for(int i = 0 ; i < 5 ; ++i){
theClass = new Class();
}

五：switch優化
範例出處：打造可維護軟體-C#版

給定一個國家GetFlagColors 回傳該國家國旗顏色

using System.Collections.Generic;
using System.Drawing;

public class NationalityColor
{
        public enum Nationality
        {
            DUTCH,
            GERMAN,
            BELGIAN,
            FRENCH,
            ITALIAN,
        }

        public IList<Color> GetFlagColors(Nationality nationality)
        {
            List<Color> result = new List<Color>();

            switch (nationality)
            {
                case Nationality.DUTCH:
                    result = new List<Color> { Color.Red, Color.White, Color.Blue };
                    break;

                case Nationality.GERMAN:
                    result = new List<Color> { Color.Black, Color.Red, Color.Yellow };
                    break;

                case Nationality.BELGIAN:
                    result = new List<Color> { Color.Black, Color.Yellow, Color.Red };
                    break;

                case Nationality.FRENCH:
                    result = new List<Color> { Color.Blue, Color.White, Color.Red };
                    break;

                case Nationality.ITALIAN:
                    result = new List<Color> { Color.Green, Color.White, Color.Red };
                    break;

                default:
                    result = new List<Color> { Color.Gray };
                    break;
            }

            return result;
        }
}

使用Dictionary 重構此程式碼

using System.Collections.Generic;
using System.Drawing;

public class NationalityColor
{
    public enum Nationality
    {
        DUTCH,
        GERMAN,
        BELGIAN,
        FRENCH,
        ITALIAN,
    }

    public Dictionary<Nationality, IList<Color>> FLAGS = new Dictionary<Nationality, IList<Color>>();

    void FlagFactoryWithMap()
    {
        FLAGS[Nationality.DUTCH] = new List<Color> { Color.Red, Color.White, Color.Blue };
        FLAGS[Nationality.GERMAN] = new List<Color> { Color.Black, Color.Red, Color.Yellow };
        FLAGS[Nationality.BELGIAN] = new List<Color> { Color.Black, Color.Yellow, Color.Red };
        FLAGS[Nationality.FRENCH] = new List<Color> { Color.Blue, Color.White, Color.Red };
        FLAGS[Nationality.ITALIAN] = new List<Color> { Color.Green, Color.White, Color.Red };
    }

    public IList<Color> GetFlagColors(Nationality nationality)
    {
        IList<Color> result;

        if (FLAGS.TryGetValue(nationality, out result))
        {
            return result;
        }

        return new List<Color> { Color.Gray }; ;
    }
}

六：避免取值及解析字串錯誤造成程式碼崩潰

Dictionary取值時建議使用：

bool isHaveValue = Dictionary.TryGetValue(TKey key, out TValue value);

字串轉數字型別：

int.TryParse(string s,out int result);

C#程式碼優化

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