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viana
Asked: 2020-10-06 05:47:16 +0800 CST 2020-10-06 05:47:16 +0800 CST

What is the difference between "@id" and "@+id"?

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When creating a view, we use @+id/fullnameto identify it.

For example:

<TextView
    android:id = "@+id/tv_fullname"
    android:layout_width = "match_parent"
    android:layout_height = "match_parent"
    android:text = "Fullname" />

What is the difference of using @id/tv_fullname(without the +), instead of @+id/ tv_fullname? Is it correct to use one or the other?

android

2 Answers

  1. @+idtells the system to generate a new id in the R.javaproject class. While @idit tells the system to use an id already generated in the class R.java.

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  2. Best Answer

    @+id : indicates the definition of an id to a resource, when we use we android:idalso indicate that an id of a resource is added inside R.javawhen your application is compiled:

    enter image description here

    public static final class id {
    public static final int myButton=0x7f0f009a;

    If you define an id to a view through android:idand you don't use @+id, it simply won't be recognized, that's why it's important to use @+id, to define that it is an id that we want to assign and this is recognized in your project.

    enter image description here

    The plus sign (+) before the resource type is needed only when you are defining a resource ID for the first time. When you build the app, the SDK tools use the ID name to create a new resource ID in your project's R.java file that references the EditText element. With the resource ID declared once in this way, other references to the identifier do not need the plus sign. Use of the plus sign is required only when specifying a new resource ID and is not required for specific resources such as strings or layouts.

    @id : indicates the reference of a resource by its id, it is actually used to access the resources defined in a project, in this case those found in R.java defined by an identifier:

    enter image description here

    It's important to mention that when the resource record was generated in R.javait doesn't matter if you use @idor @+idto get a resource reference.

    enter image description here

    I recommend you review the documentation:

    Create a simple user interface

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