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来自「C#高级编程(第三版),顶死你们。。 。up」· HTM 代码 · 共 159 行 · 第 1/2 页
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<p class="MsoNormal" style="FTEL: 0cm"><span style="FONT-FAMILY: 宋体">为了说明这一点，我们扩展上面的代码，让它使用</span><span lang="EN-US">firstStringMethod</span><span style="FONT-FAMILY: 宋体">委托在另一个对象上调用其他两个方法，其中一个方法是实例方法，另一个方法是静态方法。为此，再次使用本章前面定义的</span><span lang="EN-US">Currency</span><span style="FONT-FAMILY: 宋体">结构。</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> struct Currency</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> public uint Dollars;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> public ushort Cents;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> public Currency(uint dollars, ushort cents)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> this.Dollars = dollars;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this.Cents = cents;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> public override string ToString()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 15pt; FTEL: 18.45pt"><span lang="EN-US"> return string.Format("${0}.{1,</span><span style="FONT-FAMILY: 宋体">–</span><span lang="EN-US">2:00}", Dollars,Cents);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public static explicit operator Currency (float value)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> checked</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> uint dollars =(uint)value;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> ushort cents =(ushort)((value-dollars)*100);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> return new Currency(dollars,cents);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> public static implicit operator float (Currency value)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return value.Dollars + (value.Cents/100.0f);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 46.35pt"><span lang="EN-US">public static implicit operator Currency (uint value)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 46.2pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 50.9pt"><span lang="EN-US"> return new Currency(value, 0);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 46.2pt"><span lang="EN-US">}</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public static implicit operator uint (Currency value)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return value.Dollars;</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="MsoNormal"><span lang="EN-US">Currency</span><span style="FONT-FAMILY: 宋体">结构已经有了自己的</span><span lang="EN-US">ToString()</span><span style="FONT-FAMILY: 宋体">重载方法。为了说明如何使用带有静态方法的委托，再增加一个静态方法，其签名与</span><span lang="EN-US">Currency</span><span style="FONT-FAMILY: 宋体">的签名相同：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> struct Currency</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public static string GetCurrencyUnit()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return "Dollar";</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面使用</span><span lang="EN-US">GetAString </span><span style="FONT-FAMILY: 宋体">实例，代码如下所示：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> private delegate string GetAString();</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> static void Main(string[] args)</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> int x = 40;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> GetAString firstStringMethod = new GetAString(x.ToString);</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("String is " + firstStringMethod());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Currency balance = new Currency(34, 50);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> firstStringMethod = new GetAString(balance.ToString);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("String is " + firstStringMethod());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> firstStringMethod = new GetAString(Currency.GetCurrencyUnit);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("String is " + firstStringMethod());</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这段代码说明了如何通过委托来调用方法，然后重新给委托指定在类的不同实例上执行的不同方法，甚至可以指定静态方法，或者在类的不同类型的实例上执行的方法，只要每个方法的特征匹配于委托定义即可。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">但是，我们还没有说明把一个委托传递给另一个方法的具体过程，也没有给出任何有用的结果。调用</span><span lang="EN-US">int</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Currency</span><span style="FONT-FAMILY: 宋体">对象的</span><span lang="EN-US">ToString()</span><span style="FONT-FAMILY: 宋体">的方法要比使用委托直观得多！在真正领会到委托的用途前，需要用一个相当复杂的示例来说明委托的本质。下面就是两个委托的示例。第一个示例仅使用委托来调用两个不同的操作，说明了如何把委托传递给方法，如何使用委托数组，但这仍没有很好地说明没有委托，就不能完成很多简单的工作。第二个示例就复杂得多了，它有一个类</span><span lang="EN-US">BubbleSorter</span><span style="FONT-FAMILY: 宋体">，执行一个方法，按照升序排列一个对象数组，这个类没有委托是很难编写出来的。</span></p></div>
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<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165337.htm'><font color='red'>6.1.1 在C#中使用委托</font></a></h1>
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<div style='float:left;width:49%'>·<a href='100165325.htm'>译者序</a></div><div style='float:right;width:49%'>·<a href='100165326.htm'>前言</a></div><div style='float:left;width:49%'>·<a href='100165336.htm'>6.1 委托</a></div><div style='float:right;width:49%'>·<a href='100165338.htm'>6.1.2 简单的委托示例</a></div><div style='float:left;width:49%'>·<a href='100165339.htm'>6.1.3 BubbleSorter示例</a></div><div style='float:right;width:49%'>·<a href='100165340.htm'>6.1.4 多播委托</a></div></div>
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