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Layout attribute is not defined - Android Studio

Undeclared namespace prefix "android" (for attribute "layout_width")
How can I fix this?
This says that android is not defined.
How can I solve it? please help

try to add this in the layout
xmlns:android="http://schemas.android.com/apk/res/android
here is an example:
<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="wrap_content"
android:orientation="vertical">

Try to check some of these.
You see this error with an incorrect namespace, or a typo in the attribute. Like 'xmlns' is wrong, it should be xmlns:android
First node needs to contain: xmlns:android="http://schemas.android.com/apk/res/android"
If you are integrating AdMob, check custom parameters like ads:adSize, you need
xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
If you are using LinearLayout you might have to define tools:
xmlns:tools="http://schemas.android.com/tools"

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

Android: Adding Image to Master Detail Flow, scrolling text

I'm working on a information orientated app using the master/detail flow and so far, so good. I would like to add images to the TextView, but it's formatted differently then what I've experienced in the past and I'm lost. from my understanding of what I've read while searching is that the scrolling text is "newer" when generating the Master/detail activity, therefore I haven't found any information on this specific issue. I would also like to pass the images in using the content activity, so it would be-
addItem(new Item(ID,Name,Detail,Image1,Image2));
what the detail XML file looks like
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/bobblehead_detail"
style="?android:attr/textAppearanceMedium"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp"
android:textIsSelectable="true"
tools:context="com.example.johnson.fallout4bobbleheadlocations.BobbleheadDetailFragment" />
I tried adding ImageView's under it, but I received errors.
tl;dr I would like to add 2 images under the scrolling TextView.

I am not sure if I clearly understand what you mean but looking at your xml it seems to me that you need to add a layout (either relative or linear) to your xml file and then add a textview and two imageviews (or whatever you want) into that layout.
Something like this:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp" tools:context="com.example.somefragment">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/some_id2"
android:text="Here is your text"/>
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/some_id"
android:src="#drawable/image1"/>
<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/some_id3"
android:src="#drawable/image2"/>
</RelativeLayout>

Android: edit textview defined in xml

I have been sitting for at least 4 hours trying to solve this problem.
To understand this there are 3 files you need to know about:
eggCatcher.java which extends Activity, this class is not used for much more than
saving gamestate and showing the optionsmenu.
eggCatcherView.java which extends SurfaceView and contains "the game".
eggCatcher_layout.xml which is shown below:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/layouten">
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<easter.fun.EggCatcherView
android:id="#+id/eggcatcher"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<RelativeLayout android:id="#+id/relativeLayout1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true">
<TextView android:text="Score: "
android:id="#+id/totalscore"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true">
</TextView>
<TextView android:text="Bonus: "
android:id="#+id/bonus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true">
</TextView>
</RelativeLayout>
</FrameLayout>
</LinearLayout>
As shown in the xml file, EggCatcherView is put in the xml file.
When the applications i started the onCreate calls setContentView(layout.eggcatcher_layout);
My question now is:
how can i, from EggCatcherView.java access and edit the TextViews defined in the xmlfile?
if it was in EggCatcher.java it would be easy, just use findViewById(id.bonus), but from
inside the surfaceView appears to be a little more difficult.
I hope i have made everything clear, if you dont understand just ask!
//micke

I think you should get the parent view and then from there on you can use findViewById() (are you sure you can't just use that method anyway since SurfaceView is a subclass of View and inherits findViewById() from it?).
For using the parent you do something like:
ViewParent vp = eggCatcherView.getParent();
FrameLayout fl = (FrameLayout) vp;
TextView tx = (TextView) fl.findViewById(R.id.bonus);
Of course you need to check if the ViewParent is indeed an instance of FrameLayout.

I found this the best way:
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/hello"
android:id="#+id/test"/>
</LinearLayout>
TextView test = (TextView) findViewById(R.id.test);
test.setText("test");

If I understand correctly, you want to access the views in the surrounding activity? That seems like poor architecture. I think it would be better to either pass a callback to the EggCatcherView that can trigger methods in the Activity which in turn operate on the TextViews or fire some kind of events upwards.