android:id was added in API Level 1
This is a unique identifier name for the Button, so you can refer to the Button later in your project.
1. Add a Button in your main.xml file.
2. In the main.xml file, add the code below.
<Button
...
android:id = "@+id/myButton"
/>
3. The "+" character is required if you have not yet defined that id, if perhaps the element you reference is lower in the .xml file.
Otherwise you if it's already defined above (or included) then you can omit the "+" char:
4. Compile and run!
Related Articles:
Resources:
http://developer.android.com/reference/android/view/View.html#attr_android:id
http://developer.android.com/reference/android/R.attr.html#id
http://android-wtf.com/2012/11/difference-between-at-plus-id-and-at-id-in-android/
http://stackoverflow.com/questions/5025910/difference-between-id-and-id-in-android
http://stackoverflow.com/questions/5048586/can-you-set-tab-order-in-xml-layout
