C# WinForm控件開發(fā)設(shè)置默認(rèn)值是非常有必要的，實(shí)現(xiàn)起來也很容易，本文筆者為你介紹設(shè)置默認(rèn)值的方法，希望能給你帶來幫助。

　　如果你為屬性設(shè)定了默認(rèn)值，那么當(dāng)開發(fā)者修改了屬性的值，這個(gè)值在Property Explorer中將會(huì)以粗體顯示。VS為屬性提供一個(gè)上下文菜單，允許程序員使用C# WinForm控件開發(fā)把值重置為默認(rèn)值。

　　當(dāng)Visual Studio進(jìn)行控件的串行化時(shí)，他會(huì)判斷那些值不是默認(rèn)值，只有不是設(shè)置默認(rèn)值的屬性才會(huì)被串行化，所以為屬性提供設(shè)置默認(rèn)值時(shí)可以大大減少串行化的屬性數(shù)目，提高效率。

　　那么Visual Studio進(jìn)怎么知道我們的屬性值不是默認(rèn)值了呢？我們需要一種機(jī)制來通知Visual Studio進(jìn)默認(rèn)值。實(shí)現(xiàn)這種機(jī)制有兩種方法：

　　對(duì)于簡(jiǎn)單類型的屬性，比如Int32，Boolean等等這些Primitive類型，你可以在屬性的聲明前設(shè)置一個(gè)DefaultValueAttribute，在Attribute的構(gòu)造函數(shù)里傳入設(shè)置默認(rèn)值。

　　對(duì)于復(fù)雜的類型，比如Font，Color，你不能夠直接將這些類型的值傳遞給Attibute的構(gòu)造函數(shù)。相反你應(yīng)該提供Reset 和ShouldSerialize 方法，比如ResetBackgroundColor(),ShouldSerializeBackgroundColor()。

　　VS能夠根據(jù)方法的名稱來識(shí)別這種方法，比如Reset 方法把重置為設(shè)置默認(rèn)值，ShouldSerialize 方法檢查屬性是否是設(shè)置默認(rèn)值。過去我們把它稱之為魔術(shù)命名法，應(yīng)該說是一種不好的編程習(xí)慣，可是現(xiàn)在微軟依然使用這種機(jī)制。我還是以前面幾篇文章使用的例子代碼。

u?s?i?n?g ?S?y?s?t?e?m?.?C?o?l?l?e?c?t?i?o?n?s?.?G?e?n?e?r?i?c?;? ? ?
u?s?i?n?g ?S?y?s?t?e?m?.?T?e?x?t?;?
u?s?i?n?g ?S?y?s?t?e?m?.?W?i?n?d?o?w?s?.?F?o?r?m?s?;? ?
u?s?i?n?g ?S?y?s?t?e?m?.?C?o?m?p?o?n?e?n?t?M?o?d?e?l?;? ?
u?s?i?n?g ?S?y?s?t?e?m?.?D?r?a?w?i?n?g?;?

n?a?m?e?s?p?a?c?e ?C?u?s?t?o?m?C?o?n?t?r?o?l?S?a?m?p?l?e?
{?
p?u?b?l?i?c c?l?a?s?s ?F?i?r?s?t?C?o?n?t?r?o?l? ?:? ?C?o?n?t?r?o?l?
{?
p?r?i?v?a?t?e ?S?t?r?i?n?g? ?_?d?i?s?p?l?a?y?T?e?x?t? = "H?e?l?l?o? ?W?o?r?l?d?!";?
p?r?i?v?a?t?e ?C?o?l?o?r? ?_?t?e?x?t?C?o?l?o?r? = ?C?o?l?o?r?.?R?e?d?;?

p?u?b?l?i?c ?F?i?r?s?t?C?o?n?t?r?o?l?(?)?
{?
}?

/?/ ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t? ?i?s? ?a?n? ?e?n?u?m?e?r?a?t?i?o?n? ?d?e?f?i?n?e?d? ?i?n? ?t?h?e? ?S?y?s?t?e?m?.?D?r?a?w?i?n?g? ?
/?/ ?n?a?m?e?s?p?a?c?e? ?t?h?a?t? ?s?p?e?c?i?f?i?e?s? ?t?h?e? ?a?l?i?g?n?m?e?n?t? ?o?f? ?c?o?n?t?e?n?t? ?o?n? ?a? ?d?r?a?w?i?n?g? ?
/?/ ?s?u?r?f?a?c?e?.? ? ? ? ? ? ? ? ?
p?r?i?v?a?t?e ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t? ?a?l?i?g?n?m?e?n?t?V?a?l?u?e? = ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t?.?M?i?d?d?l?e?L?e?f?t?;?
[?C?a?t?e?g?o?r?y?("A?l?i?g?n?m?e?n?t")?,? ?D?e?s?c?r?i?p?t?i?o?n?("S?p?e?c?i?f?i?e?s? ?t?h?e? ?a?l?i?g?n?m?e?n?t? ?o?f? ?t?e?x?t?.")?]?
p?u?b?l?i?c ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t? ?T?e?x?t?A?l?i?g?n?m?e?n?t?
{?
g?e?t
{?
r?e?t?u?r?n ?a?l?i?g?n?m?e?n?t?V?a?l?u?e?;?
}?
s?e?t
{?
a?l?i?g?n?m?e?n?t?V?a?l?u?e? = ?v?a?l?u?e?;?
/?/ ?T?h?e? ?I?n?v?a?l?i?d?a?t?e? ?m?e?t?h?o?d? ?i?n?v?o?k?e?s? ?t?h?e? ?O?n?P?a?i?n?t? ?m?e?t?h?o?d? ?d?e?s?c?r?i?b?e?d? ? ? ?
/?/ ?i?n? ?s?t?e?p? ?3?.? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
I?n?v?a?l?i?d?a?t?e?(?)?;?
}?
}?

[?B?r?o?w?s?a?b?l?e?(t?r?u?e)?]?
[?D?e?f?a?u?l?t?V?a?l?u?e?("H?e?l?l?o? ?W?o?r?l?d")?]?
p?u?b?l?i?c ?S?t?r?i?n?g? ?D?i?s?p?l?a?y?T?e?x?t?
{?
g?e?t ?{? r?e?t?u?r?n ?_?d?i?s?p?l?a?y?T?e?x?t?;? ?}?
s?e?t
{?
_?d?i?s?p?l?a?y?T?e?x?t? = ?v?a?l?u?e?;?
I?n?v?a?l?i?d?a?t?e?(?)?;?
}?
}?

[?B?r?o?w?s?a?b?l?e?(t?r?u?e)?]?
p?u?b?l?i?c ?C?o?l?o?r? ?T?e?x?t?C?o?l?o?r?
{?
g?e?t ?{? r?e?t?u?r?n ?_?t?e?x?t?C?o?l?o?r?;? ?}?
s?e?t
{?
_?t?e?x?t?C?o?l?o?r? = ?v?a?l?u?e?;?
I?n?v?a?l?i?d?a?t?e?(?)?;?
}?
}?

p?u?b?l?i?c v?o?i?d ?R?e?s?e?t?T?e?x?t?C?o?l?o?r?(?)?
{?
T?e?x?t?C?o?l?o?r? = ?C?o?l?o?r?.?R?e?d?;?
}?

p?u?b?l?i?c b?o?o?l ?S?h?o?u?l?d?S?e?r?i?a?l?i?z?e?T?e?x?t?C?o?l?o?r?(?)?
{?
r?e?t?u?r?n ?T?e?x?t?C?o?l?o?r? !?= ?C?o?l?o?r?.?R?e?d?;?
}?

p?r?o?t?e?c?t?e?d o?v?e?r?r?i?d?e v?o?i?d ?O?n?P?a?i?n?t?(?P?a?i?n?t?E?v?e?n?t?A?r?g?s? ?e?)?
{?
b?a?s?e.?O?n?P?a?i?n?t?(?e?)?;?

S?t?r?i?n?g?F?o?r?m?a?t? ?s?t?y?l?e? = n?e?w ?S?t?r?i?n?g?F?o?r?m?a?t?(?)?;?
s?t?y?l?e?.?A?l?i?g?n?m?e?n?t? = ?S?t?r?i?n?g?A?l?i?g?n?m?e?n?t?.?N?e?a?r?;?

s?w?i?t?c?h ?(?a?l?i?g?n?m?e?n?t?V?a?l?u?e?)?
{?
c?a?s?e ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t?.?M?i?d?d?l?e?L?e?f?t?:?
s?t?y?l?e?.?A?l?i?g?n?m?e?n?t? = ?S?t?r?i?n?g?A?l?i?g?n?m?e?n?t?.?N?e?a?r?;?
b?r?e?a?k;?
c?a?s?e ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t?.?M?i?d?d?l?e?R?i?g?h?t?:?
s?t?y?l?e?.?A?l?i?g?n?m?e?n?t? = ?S?t?r?i?n?g?A?l?i?g?n?m?e?n?t?.?F?a?r?;?
b?r?e?a?k;?
c?a?s?e ?C?o?n?t?e?n?t?A?l?i?g?n?m?e?n?t?.?M?i?d?d?l?e?C?e?n?t?e?r?:?
s?t?y?l?e?.?A?l?i?g?n?m?e?n?t? = ?S?t?r?i?n?g?A?l?i?g?n?m?e?n?t?.?C?e?n?t?e?r?;?
b?r?e?a?k;?
}?

/?/ ?C?a?l?l? ?t?h?e? ?D?r?a?w?S?t?r?i?n?g? ?m?e?t?h?o?d? ?o?f? ?t?h?e? ?S?y?s?t?e?m?.?D?r?a?w?i?n?g? ?c?l?a?s?s? ?t?o? ?w?r?i?t?e? ? ?
/?/ ?t?e?x?t?.? ?T?e?x?t? ?a?n?d? ?C?l?i?e?n?t?R?e?c?t?a?n?g?l?e? ?a?r?e? ?p?r?o?p?e?r?t?i?e?s? ?i?n?h?e?r?i?t?e?d? ?f?r?o?m? ? ?
/?/ ?C?o?n?t?r?o?l?.? ? ? ? ? ? ? ? ? ? ? ? ?
e?.?G?r?a?p?h?i?c?s?.?D?r?a?w?S?t?r?i?n?g?(?
D?i?s?p?l?a?y?T?e?x?t?,?
F?o?n?t?,?
n?e?w ?S?o?l?i?d?B?r?u?s?h?(?T?e?x?t?C?o?l?o?r?)?,?
C?l?i?e?n?t?R?e?c?t?a?n?g?l?e?,? ?s?t?y?l?e?)?;?
}?
}?
}

　　在上面C# WinForm控件開發(fā)的代碼中，我增加了兩個(gè)屬性，一個(gè)是DisplayText，這是一個(gè)簡(jiǎn)單屬性，我們只需要在它的聲明前添加一個(gè)DefaultValue Attribute就可以了。

　　另外一個(gè)是TextColor屬性，這個(gè)復(fù)雜類型的屬性，所以我們提供了ResetTextColor和ShouldSerializeTextColor來實(shí)現(xiàn)默認(rèn)值。

　　C# WinForm控件開發(fā)設(shè)置默認(rèn)值的實(shí)現(xiàn)就講完了，但是有一點(diǎn)不要忽視了，你已經(jīng)設(shè)置默認(rèn)值，就應(yīng)該相應(yīng)的初始化這些屬性，比如我們例子中的代碼：

p?r?i?v?a?t?e ?S?t?r?i?n?g? ?_?d?i?s?p?l?a?y?T?e?x?t=”?H?e?l?l?o? ?W?o?r?l?d!”?;? ?
 p?r?i?v?a?t?e ?C?o?l?o?r? ?_?t?e?x?t?C?o?l?o?r=C?o?l?o?r?.?R?e?d?;?

　　以上介紹的就是C# WinForm控件開發(fā)如何設(shè)置屬性的默認(rèn)值，希望對(duì)你有所幫助。