The difference between @id and @+id in an Android XML file

Today, when writing an Android layout file in XML because of the use of the Lenovo function input, originally to give a control to add an ID (the correct wording should be @+ide= ""), the result is automatically associated with the @id= "". And then in the activity inside the declaration of the time is not associated with the previously defined ID. It took a while to find the definition ID wrong. Now record the difference between the two ways of writing.

　　@+id is to add a new ID to a given space that does not previously exist in the program, so it is necessary to declare a variable of the same type in the activity when used in the activity, and then reference the variable in the XML to the variable declared in the activity.

　　

@id is the ID of the reference system, in the relative SDK directory of the Ids.xml file, the general external not to call, is the component internal call when using

The difference between @id and @+id in an Android XML file