Problem with canvas in android studio

Good afternoon, I hope someone can guide me that I'm a bit lost, the problem is that I'm drawing a canvas in my project where I have an interface with 2 buttons and an editText, and at the moment of running the app the canvas covers my interface and I can not see it, the question is there is some way to send the canvas to the background or super put the interface, beforehand thanks

here the code:

package preferences.proyecto.carlos.preferences;

import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.text.Layout;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ConstraintLayout layout1 = (ConstraintLayout) findViewById(R.id.layout1);
        Lienzo fondo = new Lienzo(this);
        layout1.addView(fondo);
    }

    class Lienzo extends View{

        public Lienzo(Context context){
            super(context);
        }

        protected void onDraw(Canvas canvas){
            canvas.drawRGB(255, 255, 255);
            int ancho = canvas.getWidth();
            int alto = canvas.getHeight();
            Paint pincel1 = new Paint();
            pincel1.setARGB(255, 255, 0, 0);
            // drawLine (comienza en x,comienza en y,limite en x,limite en y,pincel)
            canvas.drawLine(70, 0, 70, alto, pincel1);
            canvas.drawLine(73, 0, 73, alto, pincel1);
            pincel1.setARGB(255, 0, 0, 255);
            int cantLineas = alto / 30;
            for (int fila = 0; fila < cantLineas; fila++) {
                canvas.drawLine(0,((fila * 60 )+ 100), ancho, ((fila * 60 )+ 100),
                        pincel1);
            }
        }
    }
}

and there's the interface:

<?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:id="@+id/layout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="preferences.proyecto.carlos.preferences.MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="8dp"
        android:text="Guardar"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="8dp"
        android:text="Borrar"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.63" />

    <EditText
        android:id="@+id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Name"
        android:layout_marginRight="8dp"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginLeft="8dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        android:layout_marginBottom="8dp"
        app:layout_constraintVertical_bias="0.23000002" />
</android.support.constraint.ConstraintLayout>