android:id was added in API Level 1
This is a unique identifier name for the CheckBox so you can refer to the CheckBox later in your project.
1. Add a CheckBox in your main.xml file.
2. In the main.xml file, add the code below between the CheckBox tags.This will name the CheckBox myCheckBox.
<CheckBox
...
android:id = "@+id/myCheckBox"
/>
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!
Next Recommended Article: Find a CheckBox using ID
Resources:
http://developer.android.com/reference/android/view/View.html#attr_android:id
http://developer.android.com/reference/android/R.attr.html#id
