SafeKeyboard/app/src/main/res/layout/activity_main.xml

<?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">

    <Button
        android:id="@+id/btnChangeIME"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="51dp"
        android:layout_marginLeft="51dp"
        android:layout_marginTop="134dp"
        android:text="切换输入法"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"></Button>

    <EditText
        android:id="@+id/et"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="292dp"
        android:focusableInTouchMode="false"
        android:hint="input text."
        android:textColor="@android:color/black"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>