C# 为类型输出格式化字符串

2024-07-03 15:40| 来源: 网络整理| 查看: 265

有两种方法可以为类型提供格式化字符串输出：

1、让类型继承IFormattable接口，实现IFormattable接口的ToString方法，需要开发者可以预见类型在格式化方面的要求。

调用输出未重写Tostring方法：

1 Person person = new Person 2 { 3 ID = "NO1", 4 FirstName = "You", 5 LastName = "Xu" 6 }; 7 Console.WriteLine(person);

输出的是类型名称：

改善1.Person

为Person类实现IFormattable接口，重写ToString方法：

1 class Person : IFormattable 2 { 3 public string ID { get; set; } 4 public string FirstName { get; set; } 5 public string LastName { get; set; } 6 7 //实现IFormattable接口的ToString方法 8 public string ToString(string format, IFormatProvider formatProvider) 9 { 10 switch (format) 11 { 12 case "Ch": 13 return this.ToString(); 14 case "Eg": 15 return string.Format("{0} {1}", FirstName, LastName); 16 default: 17 return this.ToString(); 18 } 19 } 20 21 //重写Object.ToString() 22 public override string ToString() 23 { 24 return string.Format("{0} {1}", LastName, FirstName); 25 } 26 }

调用输出修改后的代码：

1 Person person = new Person 2 { 3 ID = "NO1", 4 FirstName = "You", 5 LastName = "Xu" 6 }; 7 Console.WriteLine(person); 8 Console.WriteLine(person.ToString("Ch", null)); 9 Console.WriteLine(person.ToString("Eg", null));

输出结果：

Xu You Xu You You Xu

2、为类型自定义格式化器，可以根据需求的变化提供多个格式化器，随时增加或者修改它。

class Person { public string ID { get; set; } public string FirstName { get; set; } public string LastName { get; set; } } //Person类的格式化器 class PersonFormatter : IFormatProvider, ICustomFormatter { //实现IFprmatProvider接口 public object GetFormat(Type formatType) { if (formatType == typeof(ICustomFormatter)) { return true; } else { return false; } } //实现ICustomFormatter接口 public string Format(string format, object arg, IFormatProvider formatProvider) { Person person = arg as Person; if (person == null) { return string.Empty; } switch (format) { case "Ch": return string.Format("{0} {1}", person.LastName, person.FirstName); case "Eg": return string.Format("{0} {1}", person.FirstName, person.LastName); case "ChM": return string.Format("{0} {1}：{2}", person.LastName, person.FirstName, person.ID); default: return string.Format("{0} {1}", person.LastName, person.FirstName); } } }

调用格式化器代码：

1 Person person = new Person 2 { 3 ID = "NO1", 4 FirstName = "You", 5 LastName = "Xu" 6 }; 7 Console.WriteLine(person); 8 9 PersonFormatter pFormatter = new PersonFormatter(); 10 11 Console.WriteLine(pFormatter.Format("Ch", person,null)); 12 Console.WriteLine(pFormatter.Format("Eg", person,null)); 13 Console.WriteLine(pFormatter.Format("ChM", person, null));

输出结果，因为没有重写Object.ToString方法，类型会输出类型名称：

改善1.Person Xu You You Xu Xu You：NO1

在对IFormattable接口的ToString方法实现时，可以结合格式化器，让格式化输出在语法上支持更多的调用方式，修改ToString方法里switch结构的default部分：

1 class Person : IFormattable 2 { 3 public string ID { get; set; } 4 public string FirstName { get; set; } 5 public string LastName { get; set; } 6 7 //实现IFormattable接口的ToString方法 8 public string ToString(string format, IFormatProvider formatProvider) 9 { 10 switch (format) 11 { 12 case "Ch": 13 return this.ToString(); 14 case "Eg": 15 return string.Format("{0} {1}", FirstName, LastName); 16 default: 17 ICustomFormatter customFormatter = formatProvider as ICustomFormatter; 18 if (customFormatter == null) 19 { 20 return this.ToString(); 21 } 22 return customFormatter.Format(format, this, null); 23 } 24 } 25 26 //重写Object.ToString() 27 public override string ToString() 28 { 29 return string.Format("{0} {1}", LastName, FirstName); 30 } 31 }

调用代码：

1 Person person = new Person() 2 { 3 ID = "NO1", 4 FirstName = "You", 5 LastName = "Xu" 6 }; 7 Console.WriteLine(person); 8 9 PersonFormatter pFormatter = new PersonFormatter(); 10 11 Console.WriteLine(pFormatter.Format("Ch", person, null)); 12 Console.WriteLine(pFormatter.Format("Eg", person, null)); 13 Console.WriteLine(pFormatter.Format("ChM", person, null)); 14 15 Console.WriteLine(person.ToString("Ch", pFormatter)); 16 Console.WriteLine(person.ToString("Eg", pFormatter)); 17 Console.WriteLine(person.ToString("ChM", pFormatter));

参考：《编写高质量代码改善C#程序的157个建议》陆敏技

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