Difference between id_name and R.id.id_name

Well, because that id is stored in the variable R, although the two are the same, the id_name is simply telling you that it is of the integer type but it is stored in the variable R.

You have to use R.id_name to access the same as with other R.string elements. etc. Since all these key values are stored and classified in R.

What you mention that you can use the id_nombre directly is because you are doing a import static of the property:

import static nombreProjecto.R.id.id_nombre;

If you go to the declarations of the packages you will see the definition of the import. Actually it is the same as using R.id.id_nombre , only that with the static import you should not use the complete reference of the field id_nombre . If you want to do it with another property you will have to add the import in the declaration of the packages.

There are also 2 ways to achieve this in addition to import static :

1.

Assigning the value of R.id.id_name to a variable and it will be valid for the analyzer:

int id_name = R.id.id_name;
TextView nombre = (TextView)findViewById(id_name);

2.

Disable the studio android survey to allow you to enter any id by clicking ctrl+enter on the error - > Inspection 'Constant and Resource Type Mismatches' options - > Disable inspection:

Although it is not recommended because you would have to learn the id of the element that is an integer.

The reference of the view id_name is stored as type Int , since compiling your program generates an entry in the R.java file that refers to this resource.

For example if we create a view:

<TextView
    android:id="@+id/id_name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>

inside the file R.java that stores references of the resources of your application, an entry will be generated inside the class id :

public static final class id {
     ...
     public static final int id_name=0x7f0f0096;
     ...

Therefore you have to add R.id to be able to directly access the element reference, otherwise you will not be able to access it; Class R where the resources of your application are registered, Class id , variable id_name

findViewById(R.id.id_name)

Inside the file R.java you also have another type of classes that also define the type of elements they contain, such as:

    public static final class drawable {
          ...
          ...

   public static final class id {
          ...
          ...

   public static final class dimen {
          ...
          ...

   public static final class color {
          ...
          ...

  public static final class anim {
         ...
         ...
 public static final class array {
         ...
         ...

  

Why should I use: findViewById (R.id.id_name) and not only   findViewById (id_name)?

To access the elements within these classes it is important to add the class in which they are found, in this case id_name is within class id .