PHP中使用trait關鍵字是為了解決一個類既想整合基類的屬性和方法,下面是小編為大家整理的PHP中trait的使用方法,歡迎參考~
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123456789101112131415161718192021222324 | trait Drive { public $carName = 'trait' ; public function driving() { echo "driving {$this->carName}" ; } } class Person { public function eat() { echo "eat" ; } } class Student extends Person { use Drive; public function study() { echo "study" ; } } $student = new Student(); $student ->study(); $student ->eat(); $student ->driving(); ?> |
輸出結果如下:
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123 | study eat driving trait |
上面的例子中,Student類通過繼承Person,有了eat方法,通過組合Drive,有了driving方法和屬性carName。
如果Trait、基類和本類中都存在某個同名的屬性或者方法,最終會保留哪一個呢?
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123456789101112131415161718192021222324252627 | trait Drive { public function hello() { echo "hello drive" ; } public function driving() { echo "driving from drive" ; } } class Person { public function hello() { echo "hello person" ; } public function driving() { echo "driving from person" ; } } class Student extends Person { use Drive; public function hello() { echo "hello student" ; } } $student = new Student(); $student ->hello(); $student ->driving(); ?> |
輸出結果如下:
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12 | hello student driving from drive |
因此得出結論:當方法或屬性同名時,當前類中的方法會覆蓋 trait的 方法,而 trait 的.方法又覆蓋了基類中的方法。
如果要組合多個Trait,通過逗號分隔 Trait名稱:
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1 | use Trait1, Trait2; |
如果多個Trait中包含同名方法或者屬性時,會怎樣呢?答案是當組合的多個Trait包含同名屬性或者方法時,需要明確宣告解決衝突,否則會產生一個致命錯誤。
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123456789101112131415161718192021 | trait Trait1 { public function hello() { echo "Trait1::hello" ; } public function hi() { echo "Trait1::hi" ; } } trait Trait2 { public function hello() { echo "Trait2::hello" ; } public function hi() { echo "Trait2::hi" ; } } class Class1 { use Trait1, Trait2; } ?> |
輸出結果如下:
複製程式碼 程式碼如下:
PHP Fatal error: Trait method hello has not been applied, because there are collisions with other trait methods on Class1 in ~/php54/trait_ on line 20
使用insteadof和as操作符來解決衝突,insteadof是使用某個方法替代另一個,而as是給方法取一個別名,具體用法請看程式碼:
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1234567891011121314151617181920212223242526272829303132333435363738394041 | trait Trait1 { public function hello() { echo "Trait1::hello" ; } public function hi() { echo "Trait1::hi" ; } } trait Trait2 { public function hello() { echo "Trait2::hello" ; } public function hi() { echo "Trait2::hi" ; } } class Class1 { use Trait1, Trait2 { Trait2::hello insteadof Trait1; Trait1::hi insteadof Trait2; } } class Class2 { use Trait1, Trait2 { Trait2::hello insteadof Trait1; Trait1::hi insteadof Trait2; Trait2::hi as hei; Trait1::hello as hehe; } } $Obj1 = new Class1(); $Obj1 ->hello(); $Obj1 ->hi(); echo "" ; $Obj2 = new Class2(); $Obj2 ->hello(); $Obj2 ->hi(); $Obj2 ->hei(); $Obj2 ->hehe(); ?> |
輸出結果如下:
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1234567 | Trait2::hello Trait1::hi Trait2::hello Trait1::hi Trait2::hi Trait1::hello |
as關鍵詞還有另外一個用途,那就是修改方法的訪問控制:
Trait 也能組合Trait,Trait中支援抽象方法、靜態屬性及靜態方法,測試程式碼如下:
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1234567891011121314151617181920212223242526272829303132333435 | trait Hello { public function sayHello() { echo "Hello" ; } } trait World { use Hello; public function sayWorld() { echo "World" ; } abstract public function getWorld(); public function inc() { static $c = 0; $c = $c + 1; echo "$c" ; } public static function doSomething() { echo "Doing something" ; } } class HelloWorld { use World; public function getWorld() { return 'get World' ; } } $Obj = new HelloWorld(); $Obj ->sayHello(); $Obj ->sayWorld(); echo $Obj ->getWorld() . "" ; HelloWorld::doSomething(); $Obj ->inc(); $Obj ->inc(); ?> |
輸出結果如下:
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123456 | Hello World get World Doing something 1 2 |