Develop Reference

Where in android studio can I change the appbar text?

I'd like to change and align the text, and possibly add features on appbar in the screen above.
However, it'd be best if I could find and modify the text and align it IF I don't intend to add features.
But then I wasn't able to find where in android studio I could change the text.
I thought I could find one in the main activity xml file but I couldn't. I looked up at themes.xml and AndroidManifest.xml but couldn't find a clue.
Here is first 13 lines of my main activity xml file just in case.
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".MainActivity">
<SurfaceView
android:id="#+id/surface_view"
android:layout_width="match_parent"
android:layout_height="480dp"
app:layout_constraintTop_toTopOf="parent"/>
So, to cut it short, where in android studio can I change the text in toolbar? or appbar? above in the screen without having to create toolbar.xml? (+ align the text in the center and change text color)

Apparantly you don't have toolbar implemented in your xml layout
In Your style file make sure you set it to noActionBar
<style name="Theme.ChatApp" parent="Theme.AppCompat.Light.NoActionBar">
Then you have to add your own toolbar
<androidx.appcompat.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/toolbar"
android:background="#color/white"
app:navigationIcon="#drawable/ic_baseline_dashboard_24"
app:title="here you can put your title"/>
In your activity reference your toolbar in your onCreate
setSupportActionBar(findViewById(R.id.toolbar)
PS : If you are using MaterialToolbar please consider add this material library
implementation 'com.google.android.material:material:1.1.0'

Android fragment preloading data

Hello I'm trying to make an application that has multiple bottomnaviagtion tabs.
Currently it works because fragment data (for example, images) are static. However, if I want to make them dynamic, I'll have to create a preloader.
So I want to display a loading layout (for example R.layout.loading) UNTIL (async) function has completed and obtained data from server. Then I want to replace the layout in the fragment with a new layout (R.layout.datafragment)
Fragment onCreateView:
return inflater.inflate(R.layout.loading, container, false);
In summary it should work exactly like youtube bottom tabs.

You should create in your activity layout a placeholder for those dynamic fragments and a loader which is by default gone, but when you start loading data from the server you should make it visible (loader). Then, when you load necessary data, just start fragment transition and place whatever fragment you have loaded.

Your parent activity's layout should be like this:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<!--Navigation View and Fragment Container-->
</RelativeLayout>
<RelativeLayout
android:id="#+id/progress_layout
android:layout_width="match_parent"
android:layout_height="match_parent">
<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"/>
</RelativeLayout>
</RelativeLayout>
Then you simply show/hide progressLayout based on your requirement. Thanks

How can I change the way I display the fragments in differents display sizes?

I'm currently making an app for Android devices and I would like to know how can I change the way I display the fragments in differents display sizes (ex. Tablet).
At this point I have an activity for all my fragments and this causes me to replace the fragments when I change page but for tablets I would like to display 2 fragments inside that activity.
I've created a layout-large version for my main activity:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
tools:context=".PaginaInicial"
tools:showIn="#layout/app_bar_pagina_inicial">
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<fragment
class="pt.ipp.estg.schoolhelperapp.apontamento.ListaApontFragment"
android:id="#+id/a_fragment"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="match_parent" />
<fragment
class="pt.ipp.estg.schoolhelperapp.apontamento.VerApontFragment"
android:id="#+id/b_fragment"
android:layout_weight="2"
android:layout_width="0dp"
android:layout_height="match_parent" />
</LinearLayout>
</android.support.constraint.ConstraintLayout>
The fragment container is inside layout-small version of the main activity.
One of the fragments displays a list of items (#+id/a_fragment) and the other one displays the information of one specific item that I previously selected (#+id/b_fragment).

For further details refer to this document: https://developer.android.com/training/multiscreen/screensizes
Create a default alias resource value file in res/values/refs.xml and place the following code inside it. This value will refer to your layout file that has only one fragment.
<resources>
<item name="activity_masterdetail" type="layout">#layout/layout_with_single_fragment</item>
</resources>
Now need to create an alternative resource so that the activity_masterdetail alias will point to layout_with_two_fragment.xml on larger devices.
Create a new file with same name refs.xml but with resource qualifiers for Smallest Screen Width under Available qualifiers. Use smallest dimension of 600dp or more (sw600dp qualifier)
<resources>
<item name="activity_masterdetail" type="layout">#layout/layout_with_two_fragment</item>
</resources>
Your goal here is to have logic that works like this:
For devices that are under a specified size i.e mobile phones, use layout_with_single_fragment.xml.
For devices that are over a specified size, use layout_with_two_fragment.xml.
Now in your man activity which shows a list, use setContentView(R.layout.activity_masterDetail) i.e the name of referenced layout
If this code will run on mobile phones, normal refs.xml file will be referenced by activity_masterDetailbut if this code runs on a tablet, resource qualified refs.xml file will be used.
In your activity logic, where you want to show master and detail layout on the same screen on tables but open another activity on phones, use the following logic inside onClick() of your list items
if (findViewById(R.id.a_fragment) == null) {
Intent intent = A_Activity.newIntent(this, listItem.getId());
startActivity(intent);
} else {
Fragment newDetail = B_Fragment.newInstance(list_item.getId());
getSupportFragmentManager().beginTransaction()
.replace(R.id.b_fragment, newDetail)
.commit();
}

You should take a look at this before link it should help you understand for sure more about supporting different screen sizes.
And here is an example that you can try.

Android Studio - How to programmatically add layout_below param to CardViews inside a PercentRelativeLayout

I am here because I am trying to set programmatically the layout_below parameter of some cardViews without success.
These cardViews are located inside a PercentRelativeLayout (I do not know if it is relevant but these cardviews have been added programmatically too).
I show you the code to make it clear.
...
<android.support.percent.PercentRelativeLayout
android:id="#+id/prl"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.CardView
xmlns:percent="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="#+id/cv0"
android:layout_width="match_parent"
percent:layout_heightPercent="65%"
percent:layout_marginTopPercent="2%"
percent:layout_marginLeftPercent="2%"
percent:layout_marginRightPercent="2%"
card_view:cardCornerRadius="2dp"
card_view:cardElevation="4dp">
</android.support.v7.widget.CardView>
<android.support.v7.widget.CardView
xmlns:percent="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="#+id/cv1"
// here I would like to add android:layout_below="#+id/cv0"
android:layout_width="match_parent"
percent:layout_heightPercent="65%"
percent:layout_marginTopPercent="2%"
percent:layout_marginLeftPercent="2%"
percent:layout_marginRightPercent="2%"
card_view:cardCornerRadius="2dp"
card_view:cardElevation="4dp">
</android.support.v7.widget.CardView>
<android.support.v7.widget.CardView
xmlns:percent="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="#+id/cv2"
// here I would like to add android:layout_below="#+id/cv1"
android:layout_width="match_parent"
percent:layout_heightPercent="65%"
percent:layout_marginTopPercent="2%"
percent:layout_marginLeftPercent="2%"
percent:layout_marginRightPercent="2%"
card_view:cardCornerRadius="2dp"
card_view:cardElevation="4dp">
</android.support.v7.widget.CardView>
</android.support.percent.PercentRelativeLayout>
...
I tried to do something like this in my Java code but without success.
PercentRelativeLayout prl = (PercentRelativeLayout) view.findViewById(R.id.prl);
CardView cv = (CardView) LayoutInflater.from(getActivity()).inflate(R.layout.cv_block, prl, false);
cv.setId(currentId++);
prl.addView(cv);
cv = (CardView) LayoutInflater.from(getActivity()).inflate(R.layout.cv_block, prl, false);
cv.setId(currentId++);
RelativeLayout.LayoutParams cv_lp = (RelativeLayout.LayoutParams) cv.getLayoutParams();
cv_lp.addRule(RelativeLayout.BELOW,currentId-2);
/* I have also tried to call cv.requestLayout() but nothing changed */
prl.addView(cv);
As you can see, I am trying to generate cardviews and insert them one below the other.
Thanks in advance for your help.

PercentRelativeLayout is depreciated, so you are encouraged to use other type of layout.
This class was deprecated in API level 26.1.0.
consider using ConstraintLayout and associated layouts instead. The following shows how to replicate the functionality of percentage layouts with a ConstraintLayout. The Guidelines are used to define each percentage break point, and then a Button view is stretched to fill the gap:
ConstraintLayout gives lots of opportunities.
More about PercentRelativeLayout deprecation here.
More about ConstraintLayout and how to use it here or video tutorial.

Fragments are not running perfectly in real device

I have used fragments to define a simple splitview, in the right site i used a layout containing videoview the xml code is:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<VideoView
android:id="#+id/tvT"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>
and in the left site in another fragment layout I have defined some buttons to play different videos, The program is running well in emulators, but when I run it on device, the videoview overlapped the whole area and creates a horrible look, what should I do?

You need to post more of your code if you can; what you have posted isn't really enough for people to help you. [Edit: Darn, I thought this was trivial enough to be automatically moved to a comment on the original question :-\ ]

May you could try with "fill_parent" because the video could be to big and uses the hole display:
<VideoView
android:id="#+id/tvT"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>
If you can it would be good if you post some code how you setup your fragments.