Apps content.xml vs activity_main.xml

[NuffsaidM8]

I have just gotten started into making android apps coming from a half decent knowledge of Java. I am trying to follow this tutorial by the new boston as it was published earlier this year.

My problem is that for the life of me I cannot figure out what the content.xml file does. I'm not sure if I am just not far enough in or what, but every time he says edit the activity_main file he has solely that in his layout folder while I have that and the content.xml file in there as well. When I check the preview screen, it seems to be that the content.xml file is the file that I want to edit to add widgets (from the component tree and the general xml file code), but the preview phone thing looks exactly the same on both files even though I add the widgets to the content_main.xml file. TBH I don't even know where the came from as it did not appear in the new project creation process.

Can I get an explanation for what the difference is between the two and what I am missing?
Thanks.

 

[Deleted User]

What layout name do you use to set the content view in your activity code? Have you got that far yet?
Could be that you accidentally copied the activity_main.xml file?
Normally there is only one layout XML file associated with an activity.

The system does auto-generate certain files during the compilation process, but not in the layouts folder (AFAIK). You manually create new layout files there, to support your activity code.

 

[SergF]

think it is last update to android studio makes those tutorials a bit outdated.
it adds next novelty to "blank activity" template, so activity_main.xml that goes to setContentView looks like:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:fitsSystemWindows="true"
tools:context=".MainActivity">

<android.support.design.widget.AppBarLayout android:layout_height="wrap_content"
android:layout_width="match_parent" android:theme="@style/AppTheme.AppBarOverlay">

<android.support.v7.widget.Toolbar android:id="@+id/toolbar"
android:layout_width="match_parent" android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary" app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_main" />

<android.support.design.widget.FloatingActionButton android:id="@+id/fab"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:layout_gravity="bottom|end" android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

and second layout, named content_main.xml included/wrapped in 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"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity">

<TextView android:text="Hello World!" android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>

seems google didn't publish some guide yet on how it should be used, but seems like activity_main.xml should work like some kind of "controller/container" for app content, that will go to "content_main.xml" layout...

I suggest to start with "no activity" template and add your activity class and layout by hands for simplicity if you want just follow tutorial.

 

[NuffsaidM8]

think it is last update to android studio makes those tutorials a bit outdated.
it adds next novelty to "blank activity" template, so activity_main.xml that goes to setContentView looks like:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:fitsSystemWindows="true"
tools:context=".MainActivity">

<android.support.design.widget.AppBarLayout android:layout_height="wrap_content"
android:layout_width="match_parent" android:theme="@style/AppTheme.AppBarOverlay">

<android.support.v7.widget.Toolbar android:id="@+id/toolbar"
android:layout_width="match_parent" android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary" app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_main" />

<android.support.design.widget.FloatingActionButton android:id="@+id/fab"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:layout_gravity="bottom|end" android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

and second layout, named content_main.xml included/wrapped in 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"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity">

<TextView android:text="Hello World!" android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>

seems google didn't publish some guide yet on how it should be used, but seems like activity_main.xml should work like some kind of "controller/container" for app content, that will go to "content_main.xml" layout...

I suggest to start with "no activity" template and add your activity class and layout by hands for simplicity if you want just follow tutorial.

Thanks so much! I wasn't sure what was so weird and found no explanations in Google.