關於android xml檔案中 android:id=”@+id/my_button”的含義疑問

    許多UI開發的同學會對 android:id="@+id/my_button"的含義有所疑問，細心的同學會發現官方SDK是這樣解釋的，

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   The at-symbol (@) at the beginning of the string indicates that the XML parser should parse and expand the rest of the ID string and identify it as an ID resource. The plus-symbol (+) means that this is a new resource name that must be created and added
to our resources (in the R.java file). There are a number of other ID resources that are offered by the Android framework. When referencing an Android resource ID, you do not need the plus-symbol, but
must add the android package namespace, like so:

android:id="@android:id/empty"

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    意思也就是說 @符號要通知xml要轉換@後面的字串為ID資源，而+號表示這是要建立一個新的資源名字，並且添加到R.java檔案中。

    當你要引用已有的資源的時候 可以直接寫成 @android:id/empty