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Android Studio Dialog Buttons out of Screen when using Wrap Content as LayoutParams

I Have a Dialog with a Custom layout in my layouts Folder, which Wraps its Content. If I pu tin a large Text into one of the TextFields, the Buttons on the Bottom dissapear. The Text itself is scrollable and everything else works just fine. I want the Buttons to stick to the Bottom of the Dialog and not disappear if the text is Too Large.
Dialog without TextInput, Dialog with large Text. Icannot post Pictures directly, therefore i just included Links.
I have already tried to change the Layout so the Buttons stick to the Bottom of the Layout instead of the TextView above them. Setting a fixed size isnt really an Option.
Layout of the Dialog Layout:
<?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"
android:background="#drawable/bg_layout_rounded_16">
<EditText
android:id="#+id/dialog_resource_title"
style="#style/myEditTextStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:hint="#string/general_title_hint"
android:inputType="textMultiLine"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="#+id/dialog_resource_description"
style="#style/myEditTextStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="8dp"
android:hint="#string/general_description_hint"
android:inputType="textMultiLine"
app:layout_constraintBottom_toTopOf="#+id/dialog_resource_cancel"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/dialog_resource_title" />
<Button
android:id="#+id/dialog_resource_cancel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginEnd="4dp"
android:layout_marginBottom="8dp"
android:paddingBottom="8dp"
android:text="#string/general_cancel"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/dialog_resource_middle_line"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="#+id/dialog_resource_save"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="4dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="8dp"
android:text="#string/general_save"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="#+id/dialog_resource_middle_line" />
<android.support.constraint.Guideline
android:id="#+id/dialog_resource_middle_line"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.5" />
</android.support.constraint.ConstraintLayout>
Initialisation of the Dialog:
resourceDialog = new Dialog(context);
View v = LayoutInflater.from(context).inflate(R.layout.dialog_resource, null);
this.resourceDialogTitle = v.findViewById(R.id.dialog_resource_title);
this.resourceDialogDescription = v.findViewById(R.id.dialog_resource_description);
this.resourceDialogCancel = v.findViewById(R.id.dialog_resource_cancel);
this.resourceDialogSave = v.findViewById(R.id.dialog_resource_save);
resourceDialog.setContentView(v);
// Set Color of Root View (Otherwise white Background in the Corners)
resourceDialog.getWindow().setBackgroundDrawableResource(android.R.color.transparent);
// Getting the Display Metrics to set Size of Dialog
DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
int width = displayMetrics.widthPixels;
// Setting the Size
resourceDialog.getWindow().setLayout((width - 128), ViewGroup.LayoutParams.WRAP_CONTENT);
resourceDialog.setCanceledOnTouchOutside(false);

You can try below code to get a custom dialog:
XML Layout file (R.layout.dialog_custom_layout):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="#dimen/padding_8dp">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="User Details"
android:gravity="center"/>
<EditText
android:id="#+id/email_EditText"
android:layout_height="wrap_content"
android:hint="#string/email"
android:inputType="textEmailAddress"
android:imeOptions="actionNext"
android:maxLines="1"
android:layout_width="match_parent"/>
<EditText
android:id="#+id/password_EditText"
android:layout_height="wrap_content"
android:hint="#string/password"
android:inputType="text"
android:imeOptions="actionDone"
android:maxLines="1"
android:layout_width="match_parent"/>
<Button
android:id="#+id/btnRegister"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_marginStart="#dimen/margin_8dp"
android:layout_marginEnd="#dimen/margin_8dp"
android:layout_height="wrap_content"
android:text="Register"/>
</LinearLayout>
Kotlin code to inflate custom layout:
val alertDialog = AlertDialog.Builder(context)
val customView = LayoutInflater.from(context)
.inflate(R.layout.dialog_custom_layout, null)
val btnRegister = customView.btnRegister
alertDialog.setView(customView)
val customDialog = alertDialog.create()
customDialog.show()
btnRegister.setOnClickListener {
//perform registration
}
PS: You can change layout as per your requirement!!

Put the buttons incide a linear layout and use a constraint option to constrain it to the bottom of the screen. For example
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerInParent="true"
android:orientation="horizontal"
app:layout_constraintBottom_toBottomOf="parent">
<Button />
<Button />
</LinearLayout>
--Edit--
I tried this and worked for me
<?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">
<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fillViewport="true"
android:fitsSystemWindows="true"
android:paddingBottom="120dp"
android:scrollbars="horizontal"
app:layout_constraintTop_toBottomOf="#+id/appBarLayout">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#id/appBarLayout"
android:layout_marginLeft="10dp"
android:layout_marginTop="14dp"
android:layout_marginRight="10dp"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/address"
android:textColor="#color/black_1"
android:textSize="20sp"
android:textStyle="bold" />
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerInParent="true"
android:orientation="horizontal"
app:layout_constraintBottom_toBottomOf="parent">
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_marginRight="4dp"
android:textColor="#android:color/white" />
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_marginLeft="4dp"
android:textColor="#android:color/white" />
</LinearLayout>
</android.support.constraint.ConstraintLayout>

Try to change your EditText heigh to 0dp from wrap_content (so it won't overlap your buttons) and constraint it to one of your buttons at the bottom part of the screen:
<EditText
android:id="#+id/dialog_resource_description"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="16dp"
android:hint="some text"
android:inputType="textMultiLine"
app:layout_constraintBottom_toTopOf="#+id/dialog_resource_cancel"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/dialog_resource_title" />
Here is the full layout file:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto">
<EditText
android:id="#+id/dialog_resource_title"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:hint="general_title_hint"
android:inputType="textMultiLine"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.498"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="#+id/dialog_resource_description"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="16dp"
android:hint="some text"
android:inputType="textMultiLine"
app:layout_constraintBottom_toTopOf="#+id/dialog_resource_cancel"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/dialog_resource_title" />
<Button
android:id="#+id/dialog_resource_cancel"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginEnd="4dp"
android:layout_marginBottom="8dp"
android:paddingBottom="8dp"
android:text="general_cancel"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/dialog_resource_middle_line"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="#+id/dialog_resource_save"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="4dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="8dp"
android:text="general_save"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="#+id/dialog_resource_middle_line" />
<android.support.constraint.Guideline
android:id="#+id/dialog_resource_middle_line"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.5" />
</android.support.constraint.ConstraintLayout>

cardview not showing cornerRadius and elevation

I created a card view in a recycler view and my codes work well but the problem now is that the cardview does not show the rounded edges and elevation at runtime but it shows in the design codes. my codes are shown blow
activity_main
<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"
tools:context=".Controller.MainActivity">
<uk.co.markormesher.android_fab.FloatingActionButton
android:id="#+id/fab"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:buttonIcon="#drawable/ic_add_group"
/>
<android.support.v7.widget.RecyclerView
android:id="#+id/groupListView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
my card_view.xml
<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="wrap_content">
<android.support.v7.widget.CardView
android:id="#+id/groupCardView"
android:layout_width="match_parent"
android:layout_height="128dp"
android:layout_marginEnd="16dp"
android:layout_marginStart="16dp"
android:layout_marginTop="24dp"
app:cardCornerRadius="10dp"
app:cardElevation="5dp"
app:cardUseCompatPadding="true"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#android:color/transparent">
<TextView
android:id="#+id/groupTitle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Trips"
android:textAlignment="center"
android:textSize="30sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
</android.support.v7.widget.CardView>
I do not know what I have done wrong

Anyone could encounter this issue and the solution is very simple and caused by a mistake.there's a difference between backgroundColor and cardbackgroundColor. use setcardbackgroundColor and it should work.

You need to set
android:background="#android:color/transparent"
for main constraint, and set
app:cardBackgroundColor="#color/white"
to cardview, np

Constraint layout in practice look different than in Android Studio

I'm trying to place my views into ConstraintLayout, but every views like button/textview look different in real device than in AndroidStudio.
Check how its look:
in Android Studio
in real Device
It's looks horrible ! How I can fix that ? What I should do ?
I thought it was the easiest way to arrange views.
and my xml:
<?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"
tools:context=".activity.LoginActivity">
<Button
android:id="#+id/btnLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="228dp"
android:text="Login"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.275"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.599" />
<EditText
android:id="#+id/etLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="User"
android:inputType="textPersonName"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.498" />
<EditText
android:id="#+id/etPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Password"
android:inputType="textPassword"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.63" />
<Button
android:id="#+id/btnDefault"
android:layout_width="129dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="184dp"
android:layout_marginTop="364dp"
android:text="default user"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
</android.support.constraint.ConstraintLayout>

The idea of ConstraintLayout is to use constraints to position views relative to each other. In your case you try to constrain each view in relation to the parent and then use bias to position the view which is the reason everything seems out of order.
Here is the simple example XML that will give you a basic idea how to position these views using constraints:
<?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"
tools:context=".activity.LoginActivity">
<EditText
android:id="#+id/etLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:hint="User"
android:inputType="textPersonName"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="#+id/etPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:ems="10"
android:hint="Password"
android:inputType="textPassword"
app:layout_constraintEnd_toEndOf="#id/etLogin"
app:layout_constraintStart_toStartOf="#id/etLogin"
app:layout_constraintTop_toBottomOf="#id/etLogin" />
<Button
android:id="#+id/btnLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Login"
app:layout_constraintEnd_toStartOf="#id/btnDefault"
app:layout_constraintStart_toStartOf="#id/etLogin"
app:layout_constraintTop_toBottomOf="#id/etPassword" />
<Button
android:id="#+id/btnDefault"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="default user"
app:layout_constraintEnd_toEndOf="#id/etLogin"
app:layout_constraintStart_toEndOf="#id/btnLogin"
app:layout_constraintTop_toBottomOf="#id/etPassword" />
</android.support.constraint.ConstraintLayout>
The result:
If you want to add some spacing between the views you can experiment with adding some margins between them.

I haven't checked this for syntax, but something like this might work better (tying things to each other, rather than to the screen edges).
<?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"
tools:context=".activity.LoginActivity">
<Button
android:id="#+id/btnLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="228dp"
android:text="Login"
app:layout_constraintEnd_toEndOf="#+id/etPassword"
app:layout_constraintStart_toEndOf="#+id/btnDefault"
app:layout_constraintTop_toBottomOf="#+id/etPassword"/>
<EditText
android:id="#+id/etLogin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="64dp"
android:ems="10"
android:hint="User"
android:inputType="textPersonName"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="#+id/etPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Password"
android:inputType="textPassword"
app:layout_constraintEnd_toEndOf="#+id/etLogin"
app:layout_constraintStart_toStartOf="#+id/etLogin"
app:layout_constraintTop_toBottomOf="#+id/etLogin" />
<Button
android:id="#+id/btnDefault"
android:layout_width="129dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="184dp"
android:layout_marginTop="364dp"
android:text="default user"
app:layout_constraintStart_toStartOf="#+id/etPassword"
app:layout_constraintEnd_toStartOf="#+id/btnLogin"
app:layout_constraintTop_toBottomOf="#+id/etPassword" />
</android.support.constraint.ConstraintLayout>

Remove white border around fragment

I have a problem when i try to display a listview in my fragment, it seems like there is a white border around the fragment. I also have a similar listview displayed in an activity and it matches perfectly with the borders of the screen.
I'm gonna post below the xml file and a screenshot I took of the fragment, I hope you can help me out.
<?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">
<!-- displays the loading animation while downloading the listview -->
<RelativeLayout
android:id="#+id/loadingPanel"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center" >
<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:indeterminate="true" />
</RelativeLayout>
<TextView
android:id="#+id/tv_benvenuto"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Ecco l'elenco completo dei libri a catalogo."
android:textColor="#android:color/black"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView2" />
<ListView
android:id="#+id/lv_dashboard"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_marginTop="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/tv_benvenuto" />
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Benvenuto"
android:textColor="#android:color/black"
android:textSize="30sp"
android:textStyle="bold"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/empty"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:includeFontPadding="false"
android:text="#string/empty_dashboard"
android:textAlignment="center"
android:textSize="18sp"
android:visibility="gone"/>
</android.support.constraint.ConstraintLayout>
Image of my fragment problem

Your Listview is inheriting the Benvenuto Textview's margins as it's set to aling it. Put the views in a LinearLayout
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Benvenuto"
android:textColor="#android:color/black"
android:textSize="30sp"
android:textStyle="bold" />
<TextView
android:id="#+id/tv_benvenuto"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Ecco l'elenco completo dei libri a catalogo."
android:textColor="#android:color/black"
android:textSize="18sp" />
<ListView
android:id="#+id/lv_dashboard"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>

Sometimes when you set the width and height to match-constraint I've noticed that it adds some imaginary padding like this for whatever reason. It looks like this layout is pretty simple and just linearly goes from top to bottom in terms of its views. Why don't you just use a LinearLayout instead, and set the dimensions to matchparent? That should fix it, unless you need to add more stuff to this layout.

Layering objects in Android Studio

I'm quite new to this whole Android Studio and all, but I'm quickly getting used to it all.
Now here's my problem:
I have my main Activity with two screen-filling buttons and I want a checkbox on top of the first button.
I've looked all around the Internet, but I couldn't find a single clue.
EDIT: Messing with the order of the objects doesn't work.
This is my XML code (I haven't filled in the functionality, yet):
<?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"
tools:context="com.ggblbl.example.MainActivity">
<Button
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
android:layout_marginTop="16dp"
android:text="#string/button_one"
app:layout_constraintBottom_toTopOf="#+id/guideline"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="16dp"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
android:layout_marginTop="8dp"
android:text="#string/button_two"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="#+id/guideline"
app:layout_constraintVertical_bias="0.0" />
<android.support.constraint.Guideline
android:id="#+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_percent="0.5" />
<CheckBox
android:id="#+id/checkBox"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="#string/checkbox"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintHorizontal_bias="0.0"
android:layout_marginRight="150dp"
android:layout_marginLeft="150dp"
android:layout_marginBottom="20dp"
app:layout_constraintBottom_toTopOf="#+id/guideline" />
</android.support.constraint.ConstraintLayout>
PS: I don't know if this helps, but I use API 15 and Android Studio 2.3.2.
EDIT: I've got this
But I want this

I have removed your margins and non-needed code. Try the following layout
<?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"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="32dp"
android:text="Button 1"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintBottom_toTopOf="#+id/button2"
/>
<CheckBox
android:id="#+id/checkBox"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="CheckBox"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="#+id/button1"
/>
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="0dp"
android:text="Button 2"
app:layout_constraintTop_toBottomOf="#+id/button1"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent" />
</android.support.constraint.ConstraintLayout>
Edit: It looks like drawing over button is not possible. In the edited layout you have a bottom margin of button1 equal to height of the checkbox. You can distribute this height equally to bottom margin of button1 and top-margin of button 2. In support of my claim you can see the following layout, which gives what you want. In this example I have replaced upper button by a textview
<?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"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_height="0dp"
android:text="Button 1"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
android:background="#ddd"
app:layout_constraintBottom_toTopOf="#+id/button2"
/>
<CheckBox
android:id="#+id/checkBox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="CheckBox"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintBottom_toBottomOf="#+id/button1"
/>
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="0dp"
android:text="Button 2"
app:layout_constraintTop_toBottomOf="#+id/button1"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent" />
</android.support.constraint.ConstraintLayout>

I finally chose to abandon the use of a checkbox, as I guess it's hard-coded in that checkboxes are behind buttons.
I've found that the toggleButton does what I need too.
This one is in front of the button.