Views get stuck on Top Left Corner (Android Studio)

Question

I'm a begginer in Android Development so I decided to download Android Studio.
I created a project and in my first couple of times trying to build the App the compiler gave a an error because I was missing some files so I installed them.

My problem is that when it finally finished building the App I couldn't see the Hello Word text view even though it was displayed that it existed in the Component Tree, I add another text view and it disappeared as soon as I released the mouse button. This also happened with all the other Components that I tried with, buttons, images, views, everything.

I also noticed that by clicking one of the Components on the Component Tree in the top left corner there would show up 2 buttons: one with a symbol that imo means that it should remove the component from the Layout and another with an "ab" that I don't know what it means. This indicated me that the Components should be stuck in there for some reason.

Thank you for your attention,

João Oliveira

P.S.:

Links
Components seem to be stuck in the Top Left Corner
Text View is not visible

XML text in activity_mail.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=".MainActivity">

<TextView
    android:id="@+id/sample_text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    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="1.0" />

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView"
    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>

Answer 1

Your views are right there where you constraint them. And a view of size 1dp is not visible, this is your code:

android:layout_width="1dp"
android:layout_height="1dp"

Make the view to be the right size and you will see it.

Answer 2

    <?xml version="1.0" encoding="utf-8"?><?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=".MainActivity">

    <TextView
        android:id="@+id/sample_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        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="1.0" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TextView"
        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>