Introduction to the difference between @ id and @ + id and @ android: id in Android

Preface

Yesterday, a new colleague suddenly asked me the difference between @ id and @ + id, why our projects are @ id's own new ui @ + id

Here I said that my simple reply project is before maintenance is for unified 1 management using @ id easy to modify, because in ids. xml there is a reference, @ + id is new, do not write like that, feel a little troublesome, but in order to unified 1 finally modified to @ id, may be some of these said vague, the following is my finishing 1

Knowledge, easy to find

First of all, we need to know that the id we usually use is of int type

1 @ + id:

What we often use is that when a layout file is modified and saved, the system will automatically generate the corresponding int type variable in R. java file. The variable name is the value after "/"

For example android:id="@+id/tv" The variable is named tv

2 @ id means that an existing ID is referenced, and an ids. xml is created in R. java, such as value in res

<?xml version="1.0" encoding="utf-8"?>
<resources>
 
  <item name="text_id_text" type="id" />
  
</resources>

Our id reference

  <TextView
      android:id="@id/text_id_text"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text=" Test 1 Sub-text " />

For the convenience of modifying id, if many interfaces use the same id, we can write this (about 30 interfaces in the maintenance project use the same id)

3 @ android: id This is a reference system id itself has not been used basically, simple understanding

android: id= "@ + id/btn", which means adding a control index with id as btn in R. java file, and the most commonly used way to declare id. android: id= "@ android: id/tabhost", which means that the existing ID of the system is referenced in ids. xml under the corresponding sdk directory. 1 is not called externally, but is used when calling internally. . android: id= "@ id/btn", which means to refer to an existing ID in R. java. For example, we built an ids. xml ourselves, which declares a group of id, one of which is btn, so you can refer to it like this.

Summarize