android constrait布局与标题栏重叠

Question

What's wrong with below constraint 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:id="@+id/constraint"
    tools:context=".MainActivity">
    <Button
        android:id="@+id/button"
        android:text="Send"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="@+id/constraint"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toTopOf="@+id/txtView" />
    <TextView
        android:id="@+id/txtView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="10dp"
        android:text="Hello World!"
        app:layout_constraintTop_toBottomOf="@+id/button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        />
</android.support.constraint.ConstraintLayout>

The button has been overlapped by title bar!

Answer 1

     <Button
         android:id="@+id/toolbar"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginEnd="8dp"
         android:layout_marginRight="8dp"
         android:text="SEND"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintHorizontal_bias="0.05"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />

     <TextView
         android:layout_width="match_parent"
         android:layout_height="0dp"
         android:layout_marginBottom="8dp"
         android:layout_marginEnd="8dp"
         android:layout_marginLeft="8dp"
         android:layout_marginRight="8dp"
         android:layout_marginStart="8dp"
         android:text="Hello World"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintEnd_toEndOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@+id/toolbar"
         app:layout_constraintVertical_bias="0.0">
     </TextView>

Answer 2

Try this...

<?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:id="@+id/constraint"
  tools:context=".MainActivity">
  <Button
    android:id="@+id/button"
    android:text="Send"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    android:layout_marginLeft="8dp"
    android:layout_marginStart="8dp"
  />
  <TextView
    android:id="@+id/txtView"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_margin="10dp"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/button"/>
</android.support.constraint.ConstraintLayout>

Result: