View overlapping with Toolbar using ConstraintLayout

Used below method for add Toolbar

- <android.support.design.widget.CoordinatorLayout> or ConstraintLayout
    -<android.support.design.widget.AppBarLayout>
       - <android.support.v7.widget.Toolbar>
       - </android.support.v7.widget.Toolbar>
   - </android.support.design.widget.AppBarLayout>

  -<LinearLayout
     app:layout_behavior="@string/appbar_scrolling_view_behavior">
     -<ListView>
     -</Listview>
  -</LinearLayout>
-</android.support.design.widget.CoordinatorLayout> or ConstraintLayout

As per the official docs of ConstraintLayout :

• You need to use MATCH_CONSTRAINT (0dp) instead of MATCH_PARENT

Important: MATCH_PARENT is not recommended for widgets contained in a ConstraintLayout. Similar behavior can be defined by using MATCH_CONSTRAINT with the corresponding left/right or top/bottom constraints being set to "parent".

Just change Listview widht & height = "0dp"

<ListView
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toBottomOf="@id/app_toolbar2"/>

Try this, should work:

<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="0dp"
    android:layout_height="56dp"
    android:background="?attr/colorPrimary"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"/>

<android.support.constraint.ConstraintLayout
    android:id="@+id/main_area"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:layout_constraintTop_toBottomOf="@+id/toolbar"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent">

    <ListView
        android:id="@+id/listview"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

</android.support.constraint.ConstraintLayout>

</android.support.constraint.ConstraintLayout>