Android Studio is it normal for R.id to access eve

问题:

I am working on a little Android Studio (version 2.2.3) application.

After adding a second activity with a lot of components I noticed that when I type R.id in the first activity, the auto-completion proposes me the components from the second activity.

Is this normal ?

And here is a working example of my issue (I took the screenshot from it), for simplicity I just created two empty activities each one with a button.

AndroidManifest.xml :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myapplication">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".Main2Activity"></activity>
</application>

MainActivity.java :

package com.example.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;


public class MainActivity extends AppCompatActivity {
    private Button btMain1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //Here is the issue,
        //autocompletion of R.id. shows every layout and their composents
        btMain1 = (Button) findViewById(R.id.); 
    }
}

activity_main.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.myapplication.MainActivity">


    <Button
        android:text="Button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="198dp"
        android:id="@+id/btMain1" />
</RelativeLayout>

Main2Activity.java :

package com.example.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;

public class Main2Activity extends AppCompatActivity {
    private Button btMain2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
    }
}

activity_main2.xml :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.myapplication.Main2Activity">

    <Button
        android:text="Button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="198dp"
        android:id="@+id/btMain2" />
</RelativeLayout>

回答1:

R.java is a generated file containing all the resource identifiers for your application.

R.id is just one subclass. You also would see R.layout auto-complete, for example on setContentView

The auto-completion will pull everything because there is no isolation inside of activities, fragments, services, etc.

(snippet of mine)

/* AUTO-GENERATED FILE.  DO NOT MODIFY.
 *
 * This class was automatically generated by the
 * aapt tool from the resource data it found.  It
 * should not be modified by hand.
 */

public final class R {

    // ...

    public static final class id {
        public static final int action0=0x7f0e0090;
        public static final int action_bar=0x7f0e0060;
        public static final int action_bar_activity_content=0x7f0e0000;
        public static final int action_bar_container=0x7f0e005f;
        public static final int action_bar_root=0x7f0e005b;
        public static final int action_bar_spinner=0x7f0e0001;
        public static final int action_bar_subtitle=0x7f0e0041;

回答2:

Yes. R.id will contain every single id defined in your app. Each id is just a number, and many of them are not used in any given activity or layout.

回答3:

Your question been asked so even before I thought to learn android. Android: What is R? Why is it so Cryptic?

R is a class containing the definitions for all resources of a particular application package. It is in the namespace of the application package.

For example, if you say in your manifest your package name is com.foo.bar, an R class is generated with the symbols of all your resources in com.foo.bar.R.

There are generally two R classes you will deal with

1. The framework resources in android.R and
2. Your own in your namespace

It is named R because that stands for Resources, and there is no point in making people type something longer, especially since it is common to end up with fairly long symbol names after it, that can cause a fair amount of line wrapper.

Now in my words, If we are referencing our own resources that you have created, mostaly we use R. So android studio gives us suggestions based on that.

You should have also noticed android.R which is meant for utilizing resources built in to the operating system.

So yes you will get suggestions based on which R you use and now you should know suggestions based on that R is not for a particular Activity or view that's the reason it suggests them all.

Also there is an article, you can gain more knowledge about R.java , android.R and resources.